OSGchem5-7 - Calculations In Chemistry Modules 5-7...

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Unformatted text preview: Calculations In Chemistry Modules 5-7 On-Screen Version This is an experimental version of the lessons, designed to make it easier if you are working “from the screen,” rather than from a printed copy. This version makes it easier to “hide the answer below” while you work the problem. The Practice answers are also moved to just below the Practice problems, to make the answers easier to check when working “on screen.” To use the on-screen version: when you see the red stars ***** stop scrolling down. Work the problem on your paper. Then scroll down. The answer will be below. The regular “printed book” version will be easier to use if you are printing the lesson. The regular book version is also available on the download page. Module 5 – Word Problems......................................................................................OS 70 Lesson 5A: Lesson 5B: Lesson 5C: Lesson 5D: Lesson 5E: Lesson 5F: Lesson 5G: Answer Units -- Single Or Ratio? ...................................................................... 70 Mining The DATA .............................................................................................. 75 Solving For Single Units ..................................................................................... 80 Finding the Given ................................................................................................. 90 Some Chemistry Practice.................................................................................... 82 Area and Volume Conversions ......................................................................... 85 Densities of Solids: Solving Equations ............................................................ 93 Module 6 – Atoms, Ions, and Periodicity ............................................................OS 101 Lesson 6A: Lesson 6B: Lesson 6C: Lesson 6D: Lesson 6E: Lesson 6F: Atoms .................................................................................................................. 101 The Nucleus, Isotopes, and Atomic Mass ...................................................... 116 Atoms, Compounds, and Formulas................................................................ 114 The Periodic Table............................................................................................. 120 A Flashcard Review System............................................................................. 124 The Atoms –Part 4 ............................................................................................. 126 Module 7 – Writing Names and Formulas ..........................................................OS 127 Lesson 7A: Lesson 7B: Lesson 7C: Lesson 7D: Lesson 7E: Naming Elements and Covalent Compounds............................................... 127 Naming Ions....................................................................................................... 144 Names and Formulas for Ionic Compounds ................................................. 144 Naming Acids .................................................................................................... 159 Review Quiz For Modules 5-7 ........................................................................... 162 © 2011 www.ChemReview.Net v.n4 Page OS i Module 5 – Word Problems Module 5 – Word Problems Introduction Lessons 5A to 5E include terms and procedures that we will use to simplify problem solving for the remainder of the course. Be sure to complete all parts of Lessons 5A to 5E. In this module you will learn to identify equalities and given quantities in word problems. You will then be able to solve nearly all of the initial problems assigned in chemistry with the same conversion method used in Module 4. In addition, you will be asked to organize your data before you solve. Most students report that by using this structured approach, they have a better understanding of the steps to take to solve science calculations. ***** Lesson 5A: Answer Units -- Single or Ratio? Types of Units In these lessons, we will divide the units of measurements into three types. • Single units have one kind of base unit in the numerator, but no denominator. Examples include meters, cm3, grams, and hours. • Ratio units have one kind of base unit in the numerator and one kind in the denominator. Examples include meters/second and g/cm3 . • Complex units are all other units, such as 1/sec or (kg·meters2)/sec2. Most of the initial calculations in chemistry involve single units and ratios, but not complex units. Rules for single units will be covered in this module. Distinctions between single and ratio units will be covered in Modules 8 and 11. Rules for complex units will be addressed in Module 17. Rule #1: First, Write the WANTED Unit To solve word problems, Begin by writing “WANTED: ? ” then the unit of the answer, then an = sign. The first time you read a word problem, look only for the unit of the answer. Apply that rule to the following problem. Q. At an average speed of 25 miles/hour, how many hours will it take to go 450 miles? Begin by writing: ***** © 2011 www.ChemReview.Net v.n4 Page OS 70 Module 5 – Word Problems WANTED: ? hours = Writing the answer unit first is essential to • help you choose the correct given to start your conversions, • prompt you to write DATA that you will need to solve, and • tell you when to stop conversions and do the math. Rules for Answer Units When writing the WANTED unit, it is important to distinguish between single units and ratio units. 1. An answer unit is a ratio unit if a problem asks you to find a. “ unit X /unit Y ” or “ unit X•unit Y─1 ” or b. “ unit X per unit Y ” where there is no number after per. All of those expressions are equivalent. All are ways to represent ratio units. Example: grams , also written grams/mL or g • mL─1, is a ratio unit. mL For an answer unit, if there is no number in the bottom unit or after the word per, the number one is understood, and the WANTED unit is a ratio unit. Example: “Find the speed in miles/hour (or miles per hour)” is equivalent to “find the miles traveled per one hour.” A ratio unit means something per ONE something else. 2. An answer unit is a single unit if it has a one kind of base unit in the numerator (top term) but no denominator. Example: If a problem asks you to find grams or cm3, a single unit is WANTED. 3. If a problem asks for a “unit per more than one other unit,” it WANTS a single unit. Example: If a problem asks for “grams per 100 milliliters,” it is asking for a single unit: grams. A ratio unit must be something per one something else. Writing Answer Units 1. If you WANT a ratio unit, write the unit as a fraction with a top and a bottom. Example: If an answer unit in a problem is miles/hour, to start: Write: WANTED: ? miles = hour Do not write: WANTED: ? miles/hour or ? mph The slash mark ( / ), which is read as “per” or “over,” is an easy way to type ratios and conversion factors. However, when solving with conversions, writing ratio answer units with a clear numerator and denominator will help in arranging conversions. © 2011 www.ChemReview.Net v.n4 Page OS 71 Module 5 – Word Problems 2. If a problem WANTS a single unit, write the WANTED unit without a denominator. WANTED: ? miles = or WANTED: ? mL = Single units have a one as a denominator and are written without a denominator. Practice Cover the answers below with a sticky note or cover sheet. Then, for each problem, write “WANTED: ? ” and the unit that the problem is asking you to find, using the rules above. After that WANTED unit, write an equal sign. Do not finish the problem. Write only the WANTED unit. 1. If 1.12 liters of a gas at STP has a mass of 3.55 grams, what is the molar mass of the gas in grams/mole? 2. At an average speed of 25 miles/hour, how many minutes will it take to go 15 miles? 3. If a car travels 270 miles in 6 hours, what is its average speed? 4. A student needs 420 special postage stamps. The stamps are sold with 6 stamps on a sheet, each stamp booklet has 3 sheets, and the cost is $14.40 per booklet. How much is the cost of all of the stamps? 5. How much is the cost per stamp in problem 4? ANSWERS 1. Write WANTED: ? grams = mole 2. Write This is a ratio unit. Any unit that is in the form “unit X / unit Y” is a ratio unit. WANTED: ? minutes = This problem is asking for a single unit. If the problem asked for minutes per one mile, that would be a ratio unit, but minutes per 15 miles is asking for a single unit. 3. In this problem, no unit is specified. However, since the data are in miles and hours, the easiest measure of speed is miles per hour, written WANTED: ? miles = hour 4. WANTED: ? $ = or which is a familiar unit of speed. This problem is asking for a ratio unit. WANTED: ? dollars = 5. WANTED: ? $/stamp = or ? cents/stamp = The answer unit is a single unit. The cost per one stamp is a ratio unit. ***** © 2011 www.ChemReview.Net v.n4 Page OS 72 Module 5 – Word Problems Lesson 5B: Mining The DATA The method we will use to simplify problems is to divide solving into three parts. WANTED: DATA: SOLVE: This method will break complex problems into pieces. You will always know what steps to take to solve a problem because we will solve all problems with the same three steps. Rules for DATA To solve word problems, get rid of the words. By translating words into numbers, units, and labels, you can solve most of the initial word problems in chemistry by chaining conversions, as you did in Module 4. To translate the words, write in the DATA section on your paper every number you encounter as you read the problem, followed by its unit and a label that describes the quantity being measured. In the initial problems of chemistry, it is important to distinguish numbers and units that are parts of equalities from those that are not. To do so, we need to learn the many ways that quantities that are equal or equivalent can be expressed in words and symbols. Rules for Listing DATA in Word Problems 1. Read the problem. Write “WANTED: ?” followed by the WANTED unit and an = sign. 2. On the next line down, write “DATA:” 3. Read the problem a second time. • Each time you find a number, stop. Write the number on a line under “DATA:” • After the number, write its unit plus a label that helps to identify the number. • Decide if that number, unit, and label is paired with another number, unit, and label as part of an equality. 4. In the DATA section, write each number and unit in the problem as part of an equality a. If you see per or / (a slash). Write per or / in DATA as an equal sign (=). • If a number is shown after per or /, write the number in the equality. Example: If you read “ $8 per 3 lb. ” write in the DATA: “$8 = 3 lb.” • If no number is shown after per or /, write per as “ = 1 “ Example: If you see “25 km/hour,” write “25 km = 1 hour” Per means / or = . A per statement can be used as a conversion factor. b. Treat unit x • unit y─1 the same as unit x / unit y. Example: If you see “ 75 g • mL─1 ” write “ 75 g = 1 mL ” © 2011 www.ChemReview.Net v.n4 Page OS 73 Module 5 – Word Problems c. If the same quantity is measured using two different units. If a problem says, “0.0350 moles of gas has a volume of 440 mL,” write in your DATA: “0.0350 moles of gas = 440 mL” If a problem says a bottle is labeled “2 liters (67.6 fluid ounces),” write: “2 liters = 67.6 fluid ounces ” In both cases, the same physical quantity is being measured in two different units. d. If the same process is measured using two different units. If a problem says, “burning 0.25 grams of candle wax releases 1700 calories of energy,” write in your DATA section, “0.25 grams candle wax = 1700 calories of energy” Both sides are measures of what happened as this candle burned. After each unit, if two different entities are being measured in the problem, write a label after the unit: additional words that identify what is being measured by the number and unit. The labels “candle wax” and “energy” above will help us to identify which numbers and units to use at points during problem solving. 5. Watch for words such as each and every that mean one. One is a number, and you want all numbers in your DATA table. If you read, “Each student was given 2 sodas, ” write “ 1 student = 2 sodas” 6. Continue until all of the numbers in the problem are written in your DATA. 7. Note that when writing the WANTED unit, you write “per one” as a ratio unit and “per more than one” as a single unit. In the DATA, however, “per one” and “per more than one” are written in the same way: as an equality. Practice 1. For each phrase below, write the equality that you will add to your DATA. On each side of the equal sign, include a number and a unit, and a label if available. After every few, check your answers. a. A bottle of designer water is labeled 0.50 liters (16.9 fluid ounces). b. Every student was given 19 pages of homework. c. To melt 36 grams of ice required 2,880 calories of heat. d. The molar mass is 18.0 grams H2O•mole H2O─1. e. The dosage of the aspirin is 2.5 mg per kg of body mass. f. If 0.24 grams of NaOH are dissolved to make 250 mL of solution, what is the concentration of the solution? © 2011 www.ChemReview.Net v.n4 Page OS 74 Module 5 – Word Problems g. The car traveled at a speed of 55 miles/hour for 3 hours. 2. For Problems 1-4 in the Practice for Lesson 5A, write DATA: and then list the data equalities that are supplied in the problem. ANSWERS Terms that are equal may always be written in the reverse order. If there are two different entities in a problem, attach labels to the units that identify which entity the number and unit are measuring. 1a. 0.50 liters = 16.9 fluid ounces (Rule 4c) 1b. 1 student = 19 pages (Rule 5) 1c. 36 grams ice = 2,880 calories heat (Rule 4d) 1d. 18.0 grams H2O = 1 mole H2O (Rule 4b) 1e. 2.5 mg aspirin = 1 kg of body mass (Rule 4a) 1g. 0.24 g NaOH = 250 mL of soln. (Rule 4c) 1a. 55 miles = 1 hour (Rule 4a) 2. Problem 1. DATA: 1.12 L gas STP = 3.55 g Problem 2. DATA: 25 miles = 1 hour Problem 3. DATA: 270 miles = 6 hours (2 measures of same trip) Problem 4. DATA: 6 stamps = 1 sheet 1 booklet = 3 sheets $14.40 = 1 booklet (420 stamps is single- unit data) (The “3 hours” is single-unit data). (2 measures of same gas) (Write / as = 1) ***** Lesson 5C: Solving For Single Units Dimensional Homogeneity By the law of dimensional homogeneity, the units on both sides of an equality must be the same at the end of a calculation. One implication of this law is: if a single unit amount is WANTED in a calculation, a single-unit amount must be supplied in the data as a basis for the conversion. When a single unit is WANTED, this law will simplify using conversions. We will start each conversion calculation with an equality: “? unit WANTED = # unit given” then convert the given to the WANTED unit. DATA Formats If a Single Unit is WANTED If a problem WANTS a single unit, one number and unit in the DATA is likely to be • either a number and its unit that is not paired in an equality with other measurements, or • a number and its unit that is paired with the WANTED unit in the format “? unit WANTED = # unit given” We will define the given as the term written to the right of the equal sign in the SOLVE step: the starting point for the terms that we multiply to solve conversion calculations. © 2011 www.ChemReview.Net v.n4 Page OS 75 Module 5 – Word Problems If a problem WANTS a single-unit amount, by the laws of science and algebra, at least one item of DATA must be a single-unit amount. In problems that can be solved using conversions, often one measurement will be a single unit, and the rest of the DATA will be equalities. If a single unit is WANTED, watch for one item of data that is a single-unit amount. In the DATA, write the single number, unit, and label on a line by itself. It is a good practice to circle that single-unit amount in the DATA, since it will be the given number and unit that is used to start your conversions. For the following problem, in your notebook write only the WANTED and DATA steps above. Q. If a car’s speed is 55 miles/hr., how many minutes are needed to travel 85 miles? ***** Your paper should look like this. WANTED: ? minutes = DATA: 55 miles = 1 hour 85 miles Variations on the above rules will apply when DATA includes two amounts that are equivalent in a problem. We address these cases in Module 11. However, for the problems you are initially assigned in first-year chemistry, the rules above will most often apply. To SOLVE After listing the DATA provided in a problem, below the DATA, write SOLVE. Then, if you WANT a single unit, write the WANTED and given measurements in the format of the single-unit starting template. ? unit WANTED = # and unit given • ________________ unit given The given measurement that is written after the = sign will be the listed in the DATA. circled single unit To convert to the WANTED unit, use the equalities in the DATA (and other fundamental equalities, such as metric prefix definitions, if needed). In your notebook, finish the problem that you started above by adding the SOLVE step. Q. If a car’s speed is 55 miles/hr., how many minutes are needed to travel 85 miles? ***** © 2011 www.ChemReview.Net v.n4 Page OS 76 Module 5 – Word Problems Your paper should look like this. WANTED: ? minutes = DATA: 55 miles = 1 hour 85 miles SOLVE: ? minutes = 85 miles • 1 hour • 55 miles 60 min. = 1 hour 93 minutes You can solve simple problems without listing WANTED, DATA, SOLVE, but this 3-part method works for all problems. It works especially well for the complex problems that soon you will encounter. By using the same three steps for every problem, you will know what to do to solve all problems. That’s the goal. Summary: The 3-Step Method to Simplify Problem Solving 1. WANTED: When reading a problem for the first time, ask one question: what will be the unit of the answer? Then, write “WANTED: ?”, the unit the problem is asking for, and a label that describes what the unit is measuring. Then add an = sign. Write WANTED ratio units as x fractions and single units as single units. y 2. DATA: Read the problem a second time. • Every time you encounter a number, under DATA write the number and its unit. Add a label after the unit if possible, identifying what is being measured. • Then see if that number and unit are equal to another number and unit. If a problem WANTS a single unit, most often one measurement will be a single unit and the rest will be equalities. Circle the single unit in the DATA. 3. SOLVE: Start each calculation with an equality: ? WANTED unit = # given unit. If you WANT a single unit, substitute the WANTED and given into this format. ? unit WANTED = # and unit given • _________________ unit given Then, using equalities, convert to the WANTED unit. © 2011 www.ChemReview.Net v.n4 Page OS 77 Module 5 – Word Problems Practice Many science problems are constructed in the following format. “Equality, equality,” then, “? WANTED unit = given number and unit.” The problems below are in that format. Using the rules above, solve on these pages or by writing the WANTED, DATA, SOLVE sections in your notebook. If you get stuck, read part of the answer, adjust your work, and try again. Be sure to do problem 1. Do problem 2 if you need more practice. 1. If there are 3 floogles per 10 schmoos, 5 floogles/mole, and 3 moles have a mass of 25 gnarfs, how many gnarfs are in 4.2 schmoos? (Assume the whole numbers are exact.) WANTED: DATA: SOLVE: 2. If there are 1.6 km/mile, and one mile is 5,280 feet, how many feet are in 0.500 km? WANTED: ? DATA: SOLVE: ? © 2011 www.ChemReview.Net v.n4 Page OS 78 Module 5 – Word Problems ANSWERS 1. WANTED: ? gnarfs = 3 floogles = 10 schmoos DATA: 5 floogles = 1 mole 3 moles = 25 gnarfs 4.2 schmoos SOLVE: At the SOLVE step, first state the question, “how many gnarfs equal 4.2 schmoos?” Then add the first conversion, set up to cancel your given unit. ? gnarfs = 4.2 schmoos • ________________ schmoos Since only one equality in the DATA contains schmoos, use it to complete the conversion. ? gnarfs = 4.2 schmoos • 3 floogles 10 schmoos On the right, you now have floogles. On the left, you WANT gnarfs, so you must get rid of floogles. In the next conversion, put floogles where it will cancel. ? gnarfs = 4.2 schmoos • 3 floogles • ____________ 10 schmoos floogles Floogles is in two conversion factors in the DATA, but one of them takes us back to schmoos, so let’s use the other. ? gnarfs = 4.2 schmoos • 3 floogles 10 schmoos • 1 mole 5 floogles Moles must be gotten rid of, but moles has a known relationship with the answer unit. Convert from moles to the answer unit. Since, after unit cancellation, the answer unit is now where you WANT it, stop conversions and do the arithmetic. ? gnarfs = 4.2 schmoos • 3 floogles • 1 mole • 25 gnarfs = 4.2•3•25 gn. = 2.1 gnarfs 3 moles 10•5•3 10 schmoos 5 floogles 2. WANTED: DATA: ? feet = 1.6 km = 1 mile 1 mile = 5,280 feet 0.500 km SOLVE: ? feet = 0.500 km • 1 mile • 5,280 feet = 0.500 • 5280 feet = 1,650 feet 1.6 km 1 mile 1.6 ***** © 2011 www.ChemReview.Net v.n4 Page OS 79 Module 5 – Word Problems Lesson 5D: Finding the Given Single-Unit Givens When solving for single units, the given quantity is not always clear. For example, Q. A student needs special postage stamps. The stamps are sold 6 per sheet, each stamp booklet has 3 sheets, 450 stamps are needed, and the cost is $43.20 per 5 booklets. What is the cost of the stamps? Among all those numbers, which is the given needed as the first term when you SOLVE? For a single-unit answer, finding the given is often a process of elimination. If all of the numbers and units are paired into equalities except one, that one is your given. In your notebook, write the WANTED and DATA sections for the stamps problem above (don’t SOLVE yet). Then check your work below. ***** Answer: Your paper should look like this. WANTED: ? $= or DATA: 1 sheet = 6 stamps ? dollars = (you could also solve in cents) 3 sheets = 1 booklet 450 stamps $43.20 = 5 booklets Since you are looking for a single unit, dollars, your data has one number and unit that did not pair up in an equality: 420 stamps. That is your given. The rule is At the SOLVE step, if you WANT a single unit, start with a single unit as your given. Apply the above rule, assume all of these numbers are exact, and SOLVE the problem. ***** Answer SOLVE: If you WANT a single unit, start with a single-unit. ? $ = 450 stamps • ___________ stamps ***** © 2011 www.ChemReview.Net v.n4 Page OS 80 Module 5 – Word Problems ? $ = 450 stamps • 1 sheet • 1 booklet • $ 43.20 = 6 stamps 3 sheets 5 booklets $ 216.00 Practice For each problem below, use the WANTED, DATA, SOLVE method. If you get stuck, peek at the answers and try again. Do at least two problems. If you plan on taking physics, be sure to do problem 3. On each of these, before you do the math, double-check each conversion, one at a time, to make sure it is legal. 1. A bottle of drinking water is labeled “12 fluid ounces (355 mL).” What is the mass in centigrams of 0.55 fluid ounces of the H2O? (Use the definition of one gram). 2. You want to mail a large number of newsletters. The cost is 18.5 cents each at special bulk rates. The weight of exactly 12 newsletters is 10.2 ounces. The entire mailing weighs 125 lb. (16 ounces (oz.) = 1 pound (lb.). a. How many newsletters are being mailed? b. What is the cost of the mailing in dollars? 3. If the distance from an antenna on Earth to a geosynchronous communications satellite is 22,300 miles, given that there are 1.61 kilometers per mile, and radio waves travel at the speed of light (3.0 x 108 meters/sec), how many seconds does it take for a signal from the antenna to reach the satellite? ANSWERS 1. WANTED: ? cg = DATA: 12 fl. oz = 355 mL 0.55 fl. oz 1.00 g H2O(l) = 1 mL H2O(l) (metric definition of one gram) SOLVE: ? cg = 0.55 fl. oz. • 355 mL • 1.00 g H2O(l) • 1 cg = 1,600 cg 12 fl. oz 1 mL H2O(l) 10─2 g 2a. WANTED: ? newsletters DATA: 18.5 cents = 1 newsletter 12 exact newsletters = 10.2 ounces 16 oz. = 1 lb. 125 lb. SOLVE: (a definition with infinite sf) ? newsletters = 125 lb. • 16 oz. • 12 newsls = 2,350 newsletters 1 lb. 10.2 oz. © 2011 www.ChemReview.Net v.n4 Page OS 81 Module 5 – Word Problems 2b. WANTED: ? dollars (Strategy: Since you want a single unit, you can start over from your single given unit (125 lb.), repeat the conversions above, then add 2 more. Or you can start from your single unit answer in Part a. In problems with multiple parts, to solve for a later part, using an answer from a previous part often saves time. ) same as for Part a. DATA: SOLVE: WANTED: ? seconds = DATA: 3. ? dollars = 2,350 newsls • 18.5 cents • 1 dollar = $ 435 1 newsl 100 cents 22,300 miles 1.61 km = 1 mile 3.0 x 108 meters = 1 sec SOLVE: = 22,300 • 1.61 • 103 sec = 0.12 s ? sec = 22,300 mi. • 1.61 km • 103 meters • 1 s 8m 3.0 x 108 1 mile 1 km 3.0 x 10 (This means that the time up and back for the signal is 0.24 seconds. You may have noticed this onequarter-second delay during some live broadcasts which bounce video signals off satellites but use faster land-lines for audio, or during overseas communications routed through satellites.) ***** Lesson 5E: Some Chemistry Practice Listing Conversions and Equalities Which is the best way to write DATA pairs: as equalities or in the fraction form as conversion-factor ratios? Mathematically, either form may be used. In DATA: the equalities 1.61 km = 1 mile 3.0 x 108 meters = 1 sec. can be listed as 1.61 km , 1 mile 3.0 x 108 meters 1 sec. In these lessons, we will generally write equalities in the DATA section. This will emphasize that when solving problems using conversions, you need to focus on the relationship between two quantities. However, listing the data in the fraction format is equally valid. Data may be portrayed both ways in science texts. Why “Want A Single Unit, Start With A Single Unit?” Mathematically, the order in which you multiply conversions does not matter. You could solve with your single-unit given written anywhere on top in your chain of conversions. However, if you start with a ratio as your given when solving for a single unit, there is a 50% chance of starting with a ratio that is inverted. If this happens, the units will never cancel correctly, and you would eventually be forced to start the conversions over. Starting © 2011 www.ChemReview.Net v.n4 Page OS 82 Module 5 – Word Problems with the single unit is a method that uses dimensional homogeneity to automatically arrange your conversions “right-side up.” Practice Let’s do some chemistry. The problems below supply the DATA needed for conversion factors. In upcoming modules, you will learn how to write these conversions automatically even when the problem does not supply them. That small amount of additional information is all that you will need to solve most initial chemistry calculations. You’re ready. For problems 1-3, solve two of these problems in your notebook now and one in your next study session. Do include chemical formulas after units. Don’t let strange terms like moles or STP bother you. You’ve done gnarfs. You can do these. 1. Water has a molar mass of 18.0 grams H2O per mole H2O. How many moles of H2O are in 450 milligrams of H2O? 2. If one mole of all gases has a volume of 22.4 liters at STP, and the molar mass of chlorine gas (Cl2) is 71.0 grams Cl2 per mole Cl2 , what is the volume, in liters, of 28.4 grams of Cl2 gas at STP ? 3. If 1 mole of H2SO4 = 98.1 grams of H2SO4 and it takes 2 moles of NaOH per 1 mole of H2SO4 for neutralization, how many liters of a solution that is 0.240 mol NaOH/liter is needed to neutralize 58.9 grams of H2SO4? 4. On the following table, fill in the names and symbols for the atoms in the first 3 rows and the first 2 and last 2 columns. © 2011 www.ChemReview.Net v.n4 Page OS 83 Module 5 – Word Problems Periodic Table 1A 2A 3A 4A 5A 6A 7A ***** ANSWERS WANTED: ? moles H2O = DATA: 1. 18.0 grams H2O = 1 mole H2O 450 mg H2O SOLVE: (You WANT a single unit: moles. Start with a single unit.) © 2011 www.ChemReview.Net v.n4 Page OS 84 8A Module 5 – Word Problems ? moles H2O = 450 mg H2O • 10─3 g • 1 mole H2O = 2.5 x 10─2 moles H2O 1 mg 18.0 g H2O Write chemistry data in 3 parts: Number, unit, formula. Writing complete labels will make complex problems easier to solve. 450 has 2 sf. 2. WANTED: ? L Cl2 DATA: 1 mole gas = 22.4 L gas (always attach chemical formulas, if known, to units) 71.0 g Cl2 = 1 mole Cl2 SOLVE: 28.4 g Cl2 (Want a single unit? Start with a single unit.) ? L Cl2 = 28.4 g Cl2 • 3. 1 mole Cl2 • 22.4 L Cl2 = 8.96 L Cl 2 71.0 g Cl2 1 mole Cl2 WANTED: ? L NaOH solution DATA: 1 mole H2SO4 = 98.1 grams H2SO4 2 moles NaOH = 1 mole H2SO4 (assume whole numbers are exact) 0.240 moles NaOH = 1 liter NaOH solution 58.9 grams H2SO4 SOLVE: ? L NaOH = 58.9 g H2SO4 • 1 mole H2SO4 • 2 mole NaOH • 1 L NaOH soln. = 5.00 L NaOH soln. 98.1 g H2SO4 1 mole H2SO4 0.240 mole NaOH ***** Lesson 5F: Area and Volume Conversions Pretest: If you think you know this topic, try the last two problems in the lesson. If you can do that problem, you may skip the lesson. ***** Area Area is two-dimensional space. The area of a 3 inch by 5 inch card is _________________ (fill in the blank) ***** 15 in2, which is read as “15 square inches.” © 2011 www.ChemReview.Net v.n4 Page OS 85 Module 5 – Word Problems For area calculations, the rules are Rule A1. Area, by definition, is distance squared. All units that measure area can be related to distance units squared. Rule A2. Any unit that measures distance can be used to define an area unit. The area unit is simply the distance unit squared. Rule A3. Any equality that relates two distance units can be used as an area conversion by squaring both sides of the distance conversion. Rule A4. In conversions, write “square units” as units2. By Rule A2, area units can be any distance unit squared, such as square centimeters, square kilometers, or square miles. Using Rule A3, we can calculate a conversion factor between any two area units that are distance units squared by starting from the distance to distance equality. For example: Since 1 mile = 1.61 km is a distance conversion, and any equality that is squared on both sides remains true, (1 mile)2 = (1.61 km)2 12 mile2 = (1.61)2 km2 1 mile2 = 2.59 km2 which can be used as an area conversion. Based on the above, you can say that “one square mile is equal to 2.59 square kilometers.” Note that in squaring an equality, all parts (each number and unit) must be squared. When an area conversion based on a distance conversion is needed, the area conversion can be calculated separately, as above. However, the area conversion can also be constructed in or after the given as part of your chained conversions when you SOLVE. The logic: any two quantities that are equal can be used as a conversion factor. Since the value of any conversion factor = 1, and both sides of an equation can be taken to a power and the equation will still be true, then if A = B , then A = 1 and B () A B 2 = 12 = 1 = A2 B2 Since A2/B2 and (A/B)2 both equal 1, both are legal conversion factors. The general rule is: Any distance to distance equality or conversion can be squared and used as an area conversion, or cubed and used as a volume conversion. © 2011 www.ChemReview.Net v.n4 Page OS 86 Module 5 – Word Problems Use that rule to complete this un-finished conversion, solve, then check below. ? miles2 = 75 km2 • ( ***** 1 mile 1.61 km ) For km2 in the given to cancel and convert to miles2 on top, square the miles-to-km distance conversion. As above, when you square the conversion, be sure to square everything (each number and each unit) inside the parentheses. Adjust your work and finish if needed. ***** ? miles2 = 75 km2 • ( 1 mile 1.61 km ) 2 = 75 km2 • 12 mile2 (1.61)2 km2 = 75 miles2 = 29 miles2 2.59 The result above means that the given 75 square kilometers is equal to 29 square miles. Practice A 1. If 25.4 mm = 1 inch and 12 inches = 1 foot a. ? in. = 1.00 mm b. ? in2 = 1.00 mm2 c. ? mm2 = 2.00 ft2 2. A standard sheet of notebook paper has dimensions of 8.50 x 11.0 inches. a. What is the area of one side of the sheet of paper, in square inches? b. Using your part a answer and 2.54 cm = 1 inch , calculate the area of one side of the sheet of paper in square centimeters. 3. Under the grid system used to survey the American Midwest, a section, which is one square mile, is 640 acres. The smallest unit of farm land typically surveyed was a “quarter quarter section” of 40 acres. If 1 mile = 1.61 km, 40.0 acres is how many km2? © 2011 www.ChemReview.Net v.n4 Page OS 87 Module 5 – Word Problems ANSWERS Practice A 1. a. ? in. = 1.00 mm • 1 inch = 0.0394 in. 25.4 mm b. ? in2 = 1.00 mm2 • ( 2 = 1.00 mm2 • 12 in2 1 inch = 1 in2 = 0.00155 in2 645 25.4 mm (25.4)2 mm 2 ) ()( ) c. ? mm2 = 2.00 ft2 • 12 in. 2 • 1 ft. 25.4 mm 2 = 2.00 ft2 • (12)2 in2 • (25.4)2 mm2 = 1.86 x 1 in 105 mm2 12 in2 12 ft2 2. a. Area = length x width = 8.50 in. x 11.0 in. = 93.5 in2 b. WANT: DATA: (The unit must be included and correct). ? cm2 (a wanted single unit) 2.54 cm = 1 inch 93.5 in2 (a ratio) (a single unit. Answers from earlier parts are DATA for later parts) ***** SOLVE: (Want a single unit? Start with the single unit in the data as your given) ? cm2 = 93.5 in2 • WANTED: ? km2 DATA: 3. () 2.54 cm 2 = 93.5 in2 • (2.54)2 cm2 = 603 cm2 1 in 12 in2 1.61 km = 1 mile (in conversions, use exponents for squared, cubed) 1 section = 1 mile2 = 640 acres (any two equal terms can be used as a conversion) 40.0 acres (the single unit to use as your given) ***** SOLVE: ? km2 = 40.0 acres • 1 mile2 • 640 acres © 2011 www.ChemReview.Net v.n4 ( 1.61 km 1 mile ) 2= 40 mi2 • 2.59 km2 = 0.162 km2 640 1 mi2 Page OS 88 Module 5 – Word Problems Volume Volume, by definition, is distance cubed. Note that in each of the following equations used to calculate the volume of solids, measurements of distance are multiplied three times. • Volume of a rectangular solid = l x w x h • Volume of a cylinder = π r2 h and Volume of a sphere = 4/3 π r3 The rules for volume calculations using distance units parallel those for area calculations. Rule V1. Volume, by definition, is distance cubed. All units that measure volume can be related to distance units cubed. Rule V2. Any unit that measures distance can be used to define a volume unit. The volume unit is simply the distance unit cubed. Rule V3. Any equality that relates two distance units can be used as a volume conversion factor by cubing both sides of the distance conversion. Rule V4. In conversions, write “cubic units” as units3 (cubic meters = m3 ) In chemistry, volume units are used more often than area units. Some key relationships used in distance and volume calculations are metric fundamental rules 4 and 5: 4. 1 cm3 = 1 cc = 1 mL and 5. A cube that is 10 cm x 10 cm x 10 cm = 1 dm x 1 dm x 1 dm = = 1,000 cm3 = 1,000 mL = 1 L = 1 dm3 (see Lesson 2A.) In the English measurement system, volume units include fluid ounces, teaspoons, tablespoons, cups, quarts, and gallons. However, any English distance unit, such as inches, feet, or miles, can also be used to define a volume unit, such as in3, ft3, and miles3. A conversion that can be used to convert between English and metric volume units is the “soda can” equality: 12.0 fluid ounces = 355 mL. The conversions that we will use most frequently are based on Volume Rule 3: any distance to distance equality can be cubed to serve as a volume conversion. For example, since 1 foot ≡ 30.48 cm and since 1 km ≡ 103 m , 1 foot3 ≡ (30.48)3 cm3 = 28,317 cm3 , 1 km3 ≡ (103)3 m3 = 109 m3 Each number and each unit must be cubed when an equality is cubed. This general rule applies to both area and volume conversions: A conversion factor written as a fraction or equality can be taken to any power needed in order to cancel units, and the conversion will remain legal (equal to one). © 2011 www.ChemReview.Net v.n4 Page OS 89 Module 5 – Word Problems Use that rule to solve this problem. Q. Lake Erie, the smallest Great Lake, holds an average 485 km3 of water. What is this volume in cubic miles? (1.61 km = 1 mile). ***** (in calculations, write cubic units as units3.) WANTED: ? miles3 DATA: 1.61 km = 1 mile 484 km3 SOLVE: ? miles3 = 485 km3 • ( 1 mile 1.61 km ) The unit you WANT, miles3 , is a single unit by our definitions, though it has a power. The unit km3 in the DATA is also single unit data. Want a single unit? Start with a single unit. The above conversion is un-finished. Complete it, solve, then check below. ***** To get the given km3 to convert to miles3, use the miles-to-km distance conversion, cubed. When cubing the conversion, be sure to cube everything inside the parentheses. ***** ? miles3 = 485 km3 • () 1 mile 3 = 485 km3 • 13 mi.3 = 485 mi.3 = 116 miles3 4.17 1.61 km (1.61)3 km3 To cube 1.61, either multiply 1.61 x 1.61 x 1.61 or use the yx function on your calculator. © 2011 www.ChemReview.Net v.n4 Page OS 90 Module 5 – Word Problems Practice B Use the conversions above. Do at least every other problem now, but save one or two until prior to your test on this material. The more challenging problems are at the end. If you get stuck, read a part of the answer, then try again. Be sure to do problem 4. 1. If one mile = 1.61 km, solve: ? km3 = 5.00 miles3 2. How many cubic millimeters are in one cubic meter? 3. If 25.4 mm = 1 inch, how many cubic inches are equal to 1.00 cubic millimeters? 4. 0.355 liters a. is how many cubic centimeters? b. Using 12 in. = 1 foot and 1 in. = 2.54 cm , convert your part a answer to cubic feet. 5. ? dm3 = 67.6 fluid ounces (Finish. Include the soda-can conversion.) 6. The flathead V-twin engine on the 1947 Indian Chief motorcycle has a 74 cubic inch displacement. What is this displacement in cc’s? (Use your inches to cm conversion.) 7. Each minute, the water flow over Niagara Falls averages 1.68 x 105 m3. What is this flow a. In cubic feet? (1 meter = 3.28 feet) b. In gallons? (1 gallon = 3.79 liters) 8. Introduced in 1960, the Chevrolet big block engine, when configured with dual fourbarrel carburetors and 11.3:1 compression, developed 425 horsepower at 6200 RPM. The cylinders of this hydrocarbon-guzzling behemoth displaced 6.70 L. Immortalized by the Beach Boys, what is this displacement in cubic inches? (Use in. to cm) ANSWERS Practice B (Conversions other than those below can be used if they arrive at the same answer.) 1. ? km3 = 5.00 miles3 • 2. ? mm3 = 1 meter3 • 3. ? in3 = 1.00 mm3 • ( ) ) ) 1.61 km 1 mile ( ( 3 = 5.00 mi3 • 4.17 km3 = 20.9 km3 1 mi3 3 = 1 meter3 • 13 mm3 1 mm = 1 x 109 mm3 10─3 meter 10─9 meter3 3 = 1.00 mm3 • 13 in3 1 inch = 6.10 x 10─5 in3 25.4 mm (25.4)3 mm3 4. a. ? cm3 = 0.355 L • 1,000 cm3 = 355 cm3 1L b. ? ft3 = 355 cm3 • ( 1 inch 3 • 2.54 cm © 2011 www.ChemReview.Net v.n4 (metric fundamentals) 1 foot 3 = 355 cm3 • 13 in3 • 13 ft3 = 0.0125 ft3 12 in (2.54)3 cm3 (12)3 in3 )( ) Page OS 91 Module 5 – Word Problems 5. ? dm3 = 67.6 fl. oz. • 355 mL • 12.0 fl oz. 1 dm3 = 2.00 dm3 1L 3 = 74 in3 • (2.54)3 cm3 = 1,200 cm3 = 1,200 cc’s 13 in3 6. ? cc’s = ? cm3 = 74 in3 • 7a. ? ft3 = 1.68 x 105 m3 • 10─3 L • 1 mL ( 2.54incm ) 1 () 3.28 ft 1 meter 3 = 1.68 x 105 m3 • (3.28)3 ft3 (1)3 m3 = 5.93 x 106 ft3 7b. Hint: 1 m = 10 dm , 1 dm3 = 1 liter ***** ? gallons = 1.68 x 105 m3 • () 10 dm 3 • 1 L • 1 gal = 1.68 x 108 gal. = 4.43 x 107 gallons 1 meter 1 dm3 3.79 L 3.79 8. WANTED: ? in3 displacement DATA: 6.70 L displacement 1 inch = 2.54 cm (metric-English bridge) ***** Strategy: This problem includes numbers you don’t need. Since a displacement is wanted, start with a displacement as your given, then head for the cm needed in the metric part of the metric/English bridge conversion. ***** SOLVE: ? in3 = 6.70 L • 1,000 cm3 • 1L ***** © 2011 www.ChemReview.Net v.n4 ( 1 in 2.54 cm ) 3 = 6,700 cm3 • 1 in3 = 409 in3 (2.54)3 cm3 Page OS 92 Module 5 – Word Problems Lesson 5G: Density and Solving Equations Pretest: If you think you know this topic, try the last problem in the lesson. If you can do that problem, you may skip the lesson. ***** Solving Problems Using Mathematical Equations Calculations in chemistry can generally be solved using conversions, mathematical equations, or both. Conversions can be used for problems in which all of the relationships can be expressed as two quantities that are equal or equivalent. Equations are required for more complex relationships. In these lessons, when we study gas laws and energy, we will discuss in detail the circumstances in which equations must be used. Many problems can be solved with either conversions or equations. Conversion methods usually involve less memorization, less algebra, and fewer steps. For most of the early topics in first-year chemistry courses, conversions are the easier way to solve. An exception is problems involving the density of substances that are in geometric shapes. To calculate substance volumes, these problems require mathematical equations. (In these lessons, we will call mathematical formulas equations, and reserve the term formula for chemical formulas.) Volumes for regular geometric shapes are calculated using equations, including • Volume of a cube = (side)3 • Volume of a rectangular solid = l x w x h • Volume of a cylinder = π r2 h • Volume of a sphere = 4/3 π r3 Density is defined as mass per unit of volume. In equation form: D = m/V . Because density is the ratio between mass and volume, it can be used as a conversion factor. Some calculations involving density may be solved using either conversions or the density equation, but in many density problems, equations are required to calculate the volume of a geometric shapes such as a cylinder or a sphere. If an equation is used for one part, by using the D = m/V equation for the other part, the same equation-solving method can be used to solve both parts of the problem. In a density problem that requires a geometric volume calculation, both the density equation and the geometric volume equations include volume as one of the terms. If we can solve for volume in one equation, we can use that volume to solve for quantities in the other equation. In general, if a problem involves two equations linked by a common quantity, a useful method to solve is to • list the equations and DATA for the two equations in separate columns. © 2011 www.ChemReview.Net v.n4 Page OS 93 Module 5 – Word Problems • Find the value of the linked quantity in the column with one missing variable instead of two (usually the column that does not include the WANTED quantity), then • Add the value of the linked quantity to the other column and solve for the WANTED quantity. Let us learn this method by example. Q. If aluminum (Al) has a density of 2.7 g/cm3, and a 10.8 gram Al cylinder has a diameter of 0.60 cm, what is the height of the cylinder? (Vcylinder = π r2h) Do the following steps in your notebook. 1. First, read the problem and write the answer unit. WANTED = ? unit and label. 2. To use conversions, at this point we would list the problem’s numbers and units, most of them in equalities. However, if you see a mathematical equation is needed to solve the problem, write that equation in your DATA instead, and draw a box around it. Then, under the equation, list each symbol in the equation, followed by an = sign. 3. If two equations are needed to solve the problem, write and box the two equations in two separate columns. Under each equation, write the symbol for each variable in that equation. (Simple numeric constants, such as 4/3 or π , can be left out of the table.) 4. Usually, one symbol will be the same in both equations. Circle that linked symbol in the DATA in both columns. That symbol will have the same value in both columns. Finish those steps and then check your answer below. ***** At this point, your paper should look like this. WANTED: DATA: ? cm height Al cylinder = Vcylinder = π r2 h Density = mass/Volume V= D= r= m= h= V= Next, do the following steps. 5. Write “= ? WANTED” after the symbol that is WANTED in the problem. 6. Transfer the problem data to the DATA table. After each symbol in the DATA, write the number and unit in the problem that corresponds to that symbol. Use the units of the numbers to match up the symbols: grams is mass, mL or cm3 is volume, etc. © 2011 www.ChemReview.Net v.n4 Page OS 94 Module 5 – Word Problems 7. After any remaining symbol that does not have DATA in the problem, write a ?. After you have finished those steps, check your answer below. ***** Your DATA table should look like this. DATA: Vcylinder = π r2 h Density = mass/Volume V=? D = 2.7 g/cm3 r = 1/2 diameter = 0.30 cm m = 10.8 grams h = ? WANTED V= ? 8. A fundamental rule of algebra: if you know values for all of the symbols in a mathematical equation except one , you can solve for that missing symbol. If you are missing values for two symbols, you cannot solve using one equation. In the above data, column 1 has two missing values, and column 2 has one. At this point, you can solve for the missing value only in column 2. In a problem involving two relationships, usually you will need to solve first for the common, linked symbol in the column without the WANTED symbol. Then, use that answer to solve for the WANTED symbol in the other column. 9. When solving an equation, solve in symbols before you plug in numbers because in algebra, symbols move faster than numbers with units. Solve for the missing column 2 data, and then check your answer below. ***** SOLVE: (In column 2, D = m/V ; and we want V. Solve the D equation for V in symbols, then plug in the numbers for those symbols from the DATA.) D = m /V WANTED = V = m = 10.8 g D 2.7 g/cm3 = 4.0 cm3 (In the unit cancellation, 1/(1/X) = X. See Lesson 1B.) © 2011 www.ChemReview.Net v.n4 Page OS 95 Module 5 – Word Problems 10. Put this solved answer in the DATA. Since the problem is about one specific cylinder, the volume of that cylinder must be the same in both columns. Write your calculated volume in both columns. 11. Now solve the equation that contains the WANTED symbol for the WANTED symbol using the symbols, then plug in the numbers and their units. EQUATION: Vcyl. = π r2 h ; so WANTED = height = h = V = π r2 4.0 cm3 = 2 π (0.30 cm) 4.0 cm3 = 14 cm height π (0.090 cm2) SUMMARY: Steps for Solving With Equations 1. First write WANTED = ? and the unit you are looking for. 2. When you see that you need a mathematical equation to solve, under DATA, write and box the equation. 3. If you need two equations, write them in separate columns. 4. Under each equation, list each symbol in that equation. 5. Write “? WANTED” after the WANTED symbol in the problem. 6. After each symbol, write numbers and units from the problem. Use the units to match the numbers and units with the appropriate symbol. 7. Label remaining symbols without DATA with a ? 8. Circle symbols for variables that are the same in both equations. 9. Solve equations in symbols before plugging in numbers. 10. Solve for ? in the column with one ? first. 11. Write that answer in the DATA for both columns, then solve for the WANTED symbol. Flashcards: Using the table below, cover the answer column, then put a check by the questions in the left column you can answer quickly and automatically. For the others, make flashcards using the method in Lesson 2C. One-way cards (with notch at top right): Back Side -- Answers Density = Volume of a cube = Mass/Volume Volume of a sphere = 4/3 π r3 Volume of a cylinder = π r2 h © 2011 www.ChemReview.Net v.n4 (side)3 Page OS 96 Module 5 – Word Problems Practice: Practice any needed flashcards above, then try two of the problems below. Save one problem for your next study session. Use the steps for solving with equations above. Answers are at the end of this lesson. If you get stuck, read a part of the answer, and then try again. 1. What is the density of liquid water? 2. If the density of lead is 11.3 grams per cubic centimeter, what is the mass of a ball of lead that is 9.0 cm in diameter? 3. A gold American Eagle $50 coin has a diameter of 3.26 cm and mass of 36.7 grams. Assuming that the coin is in the approximate shape of a cylinder and is made of gold alloy (density = 15.5 g/mL), find the height of the cylinder (the thickness of the coin). 4. If a solid copper cube with the length on a side of 1.80 cm has a mass of 52.1 grams, what is the density of the copper, in grams per cubic centimeter? ANSWERS 1. WANTED: mass/volume ratio for liquid water. Hint: What’s the definition of one gram? ***** 1.00 g (mass) liquid water = 1 mL (volume) , so mass/volume = 1.00 g / 1 mL = 1.00 g/mL 2. WANTED: DATA: ? grams lead Vsphere = 4/3π r3 Density = mass/Volume V=? D = 11.3 g/cm3 r = 1/2 diameter = 4.5 cm m = ? WANTED V= ? Strategy: SOLVE: Column 1 has one ?, and column 2 has two. Solve column one first ? = V = 4/3 π r3 = 4/3 π (4.5 cm)3 = 382 cm3 In problems that solve in steps, carry an extra sf until the final step. Add this answer to the volume DATA in both columns. Then solve the Column 2 equation for the WANTED mass. First solve in symbols, then plug in the numbers. If needed, adjust your work, then finish. ***** © 2011 www.ChemReview.Net v.n4 Page OS 97 Module 5 – Word Problems D = m/V and mass is WANTED, WANTED = m = D ● V = 11.3 g ● 382 cm3 = 4.3 x 103 grams (2 sf ) cm 3 Units must be included and must cancel to give the WANTED unit. Use the sf in the original data to determine the sf in the final answer. You can also solve the column 2 data for grams using conversion factors. ? g = 382 cm3 • 11.3 g 1 cm 3 = 4.3 x 103 g 3. (Hint: You will need 1 mL = 1 cm3 ) ***** WANTED: ? cm height of gold cylinder (thickness of coin) DATA: Vcylinder = π r2 h D = mass/Volume V=? D = 15.5 g/mL r = 1/2 diameter = 1.63 cm m = 36.7 grams h = ? WANTED V= ? Strategy: First complete the column with one ?, then use that answer to solve for the variable WANTED in the other column. Column 1 has two ? and column 2 has one. SOLVE: D = m/V ; WANTED = V = m = 36.7 g = 2.368 mL D 15.5 g/mL (Carrying extra sig fig until end) ( 1/(1/mL) =. mL ; see Lesson 1B) Fill in that Volume in both columns. Then solve the equation that contains the WANTED symbol, first in symbols, and then with numbers. EQUATION: V = π r2 h WANTED = height = h = V = 2.368 mL π r2 π (1.63 cm)2 = 2.368 cm3 = 0.284 cm 8.347 cm2 Note carefully the unit cancellation above. By changing mL to cm3 (they are identical), the base units are consistent. They then cancel properly. A height of a cylinder, or thickness of a coin, must be in distance units such as cm. Your work must include unit s, and answers must include correct units to be correct. © 2011 www.ChemReview.Net v.n4 Page OS 98 Module 5 – Word Problems WANTED: ? grams copper cube = cm3 DATA: 4. 52.1 grams copper Side of cube = 1.80 cm Strategy: This one is tricky because you are not told that you need to calculate volume. Note, however, that you WANT grams per cubic cm. You are given grams and cm. In density problems, be on the lookout for a volume calculation. The equation for the volume of a cube is Vcube = (side)3. If you needed that hint, adjust your work and try the question again. ***** DATA: Vcube =(Side)3 D = mass/Volume V=? D = ? WANTED side = 1.80 cm m = 52.1 g copper V= ? SOLVE: First solve the column with one ? then put that answer in both columns. Volume of cube = (side)3 = (1.80 cm)3 = 5.832 cm3 Now solve for the WANTED symbol in the other equation. D = ? WANTED = mass = volume 52.1 g Cu 5.832 cm3 = 8.93 g Cu cm3 ***** Summary: Word Problems 1. To solve word problems, get rid of the words. 2. Organize your work into 3 parts: WANTED, DATA, and SOLVE. 3. First, under WANTED, write the unit you are looking for. As a part of the unit, include a label that describes what the unit is measuring. 4. If a ratio unit is WANTED, write the unit as a fraction with a top and a bottom. 5. Under DATA, to solve with conversions, • write every number in the problem. Attach the units to the numbers. If the problem involves more than one substance, add a label after the unit that identifies the substance being measured. • If numbers and units are paired with other numbers and units, write those DATA terms in an equality. © 2011 www.ChemReview.Net v.n4 Page OS 99 Module 5 – Word Problems • Write per or a slash (/) in the data as = . Treat “• unit─# “ as “ / unit# “. If no number is given after per or / or • , write = 1 . • Write as equalities two different measurements of the same entity, or any units and labels that are equivalent or mathematically related in the problem. 6. At the SOLVE step, start each calculation with an equality: ? WANTED unit = # given unit. and chain conversions to solve. If you WANT a single unit, start with a single unit as your given. 7. Any distance to distance equality or conversion can be squared and used as an area conversion, or cubed and used as a volume conversion. 8. For problems that require mathematical equations to solve, • write and box the equations in your DATA. • List each symbol in the equation below the equation. • Match the data in the problem to the symbols. • Solve in symbols before plugging in numbers. 9. For problems requiring two equations to solve, solve the two equations separately. Solve for the linked variable in the non-WANTED column first. Use that answer as DATA to solve for the WANTED symbol in the other column. ##### © 2011 www.ChemReview.Net v.n4 Page OS 100 Module 6 – Atoms, Ions, and Periodicity Module 6 – Atoms, Ions, and Periodicity Pretests: Each lesson in this module has a pretest. If you pass the pretest, you may skip the lesson. Module 6 covers fundamentals. Depending on your background, you may be able to skip several lessons or complete them very quickly. To do this module, you will need an alphabetical list of the atoms (provided on the next-tolast page of these lessons) and a periodic table that closely resembles the type of table you will be allowed to consult during quizzes and tests in your course. ***** Lesson 6A: Atoms Pretest: Using a list of atoms or a periodic table, try problem 6 at the end of this lesson. If you find problem 6 easy, you may skip to Lesson 6B. ***** Terms and Definitions The precise definition for some of the fundamental particles in chemistry is a matter of occasional debate, but following simplified and somewhat arbitrary definitions will provide us with a starting point for discussing atoms. 1. Matter. Chemistry is primarily concerned with matter and energy. Matter is anything that has mass and volume. On planets, nearly all matter is composed of extremely small particles called atoms. 2. Atoms. In these lessons, we will define an atom as a particle with a single nucleus, plus the electrons that surround the nucleus. There are 91 different kinds of atoms that are found in the Earth’s crust. More than 20 additional atoms have been synthesized by scientists using nuclear reactions. All of the millions of different substances on earth are consist of only about 100 different kinds of atoms. It is how the atoms are grouped and arranged in space that results in so many different substances. A list of the atoms is found at the end of these lessons. Each atom is represented by a one- or two-letter symbol. The first letter of the symbol is always capitalized. The second letter, if any, is always lower case. 3. Electrical charges. Some particles have a property known as electric charge. There are two types of charges, positive and negative. Particles with like electrical charges repel. Unlike charges attract. + + © 2011 www.ChemReview.Net v.n4 ─ ─ + ─ Page OS 101 Module 6 – Atoms, Ions, and Periodicity 4. Atomic structure. Atoms can be described as combinations of three subatomic particles: protons, neutrons, and electrons. a. Protons (symbol p+) Protons are found in the center of the atom, called the nucleus. Each proton has a 1+ electrical charge (one unit of positive charge) and a mass of about 1.007 amu (atomic mass units). The number of protons in an atom, also called the atomic number of the atom, determines the name (and thus the symbol) of the atom. The number of protons in an atom is never changed by chemical reactions. b. Neutrons (symbol n0) Neutrons are located in the nucleus of an atom, along with the protons. Neutrons have an electrical charge of zero but about the same mass as a proton: 1.009 amu. Neutrons are thought to act as the glue of the nucleus: particles that help to keep the repelling protons from flying apart. Neutrons, like protons, are never gained or lost in chemical reactions. The neutrons in an atom in most cases have very little influence on the chemical behavior of the atom. c. Electrons (symbol e─) Each electron has a 1─ electrical charge: one unit of negative charge, equal in magnitude but opposite the proton’s charge. Electrons have very little mass, weighing about 1/1837 amu. Electrons are found outside the nucleus of an atom, in regions of space called orbitals. Nearly all of the volume of an atom is due to the space occupied by the electrons around the nucleus. Electrons are the only subatomic particles that can be gained or lost during chemical reactions. To summarize: Charge Mass Location In Atoms During Reactions Proton +1 1.007 amu Nucleus No Change Neutron 0 1.009 amu Nucleus No Change Electron –1 0.00055 amu Orbitals May Change Particle 5. Neutral atoms. If an atom has an equal number of protons and electrons, the balance between positive and negative charges gives the atom a net charge of zero. The charges are said to “cancel” to produce an overall electrically neutral atom. © 2011 www.ChemReview.Net v.n4 Page OS 102 Module 6 – Atoms, Ions, and Periodicity Practice A Commit to memory Points 4 and 5. Then, for the problems below, consult the alphabetical list of atoms at the end of these lessons, but apply Points 4 and 5 from memory. 1. Write the symbols for these atoms. a. Sulfur b. Silicon c. Sodium d. Tungsten 2. Name the atoms represented by these symbols. a. K b. F c. Fe d. Pb 3. Assume each atom below is electrically neutral. Fill in the blanks. Atom Name Symbol Protons Electrons Atomic Number Sodium N 6 82 9 ANSWERS Part A 1a. S 1b. Si 1c. Na 1d. W 2a. Potassium 2b. Fluorine 2c. Iron 2d. Lead 3. Atom Name sodium nitrogen carbon lead fluorine © 2011 www.ChemReview.Net v.n4 Symbol Na N C Pb F Protons 11 7 6 82 9 Electrons 11 7 6 82 9 Atomic # 11 7 6 82 9 Page OS 103 Module 6 – Atoms, Ions, and Periodicity More Terms and Definitions 6. Chemical reactions cannot create or destroy atoms, nor change an atom from one kind to another. However, during a chemical reaction, how atoms are bonded and arranged changes, and this alters the identity and the behaviors of the substances involved in the reaction. 7. Physical changes. When a substance undergoes a physical change, it does not change its identity. Melting ice to water is a physical change, because both ice and liquid water are composed of particles that internally have the same atoms in the same geometry. A physical change is not considered to be a chemical reaction. 8. Ions. During chemical reactions, the number of protons and neutrons in an atom never changes, but atoms may gain or lose one or more electrons. Any particle (atom or group of bonded atoms) that does not have an equal number of protons and electrons is termed an ion, which is a particle with a net electrical charge. • Neutral particles that lose electrons become positive ions. • Neutral particles that gain electrons become negative ions. The symbol or chemical formula for a particle that is not electrically neutral places the value of the net charge as a superscript to the right of the symbol. An ion is not the same as a neutral particle with the same atom or atoms. The ion has a different number of electrons and different chemical behavior. Examples of atoms and ions a. All atoms containing 16 protons are sulfur (symbol S). A sulfur atom in its elemental state has 16 protons and 16 electrons. The symbol for the neutral sulfur atom is written as S, but S0 may also be written to emphasize that the sulfur atom has a neutral charge: the positive and negative charges balance In substances, an ion of sulfur may be found that contains 16 protons and 18 electrons. The 16 protons cancel the charge of 16 electrons, leaving two uncancelled electrons and an overall charge of 2─. The symbol for this particle is S2─ and it is named a sulfide ion. b. All atoms with 19 protons are named potassium (symbol K). Potassium is a soft metal in its elemental state. However, neutral potassium metal atoms react with many substances, including water, and each potassium atom loses one electron in all of these reactions. Because of this reactivity, in substances found in the earth’s crust, potassium is always found as an ion with 18 electrons. The 18 electrons balance the charge of 18 protons. This leaves one positive charge un-cancelled, so the ion has a net charge of 1+. This particle is named potassium ion and its symbol is K+. For the charges on ions, if no number after the sign is shown, a 1 is understood. c. All atoms with 88 protons are named radium (symbol Ra). Ra2+ ions must have how many electrons? © 2011 www.ChemReview.Net v.n4 Page OS 104 Module 6 – Atoms, Ions, and Periodicity ***** 86 Practice B 1. From memory: given symbols, write the names, from the names write symbols. a. Sr = _______________ b. I = ______________ d. Bromine = ______ e. Boron = _______ c. P = _____________ f. Barium = _____________ For the problems below, use the alphabetical list of atoms at the end of these lessons. 2. Strontium has atomic number 38. Symbol Electrons 79 79 1 0 34 a. A neutral Sr atom has how many protons? Protons 36 I─ How many electrons? b. How many protons and electrons are found in a Sr2+ ion? Al3+ 3. For the particles composed of single atoms at the right, fill in the blanks. ANSWERS Part B 1 a. Strontium b. Iodine 2. a. 38 protons, 38 electrons. c. Phosphorus d. Br eB f. Ba b. 38 protons, 36 electrons 3. Symbol Protons Electrons I─ 53 54 Au 79 79 H+ 1 0 Se2─ 34 36 Al3+ 13 10 ***** © 2011 www.ChemReview.Net v.n4 Page OS 105 Module 6 – Atoms, Ions, and Periodicity Lesson 6B: The Nucleus, Isotopes, and Atomic Mass Pretest: If you think you know this topic, try 2-3 parts of each practice set. If you can do those correctly, skip the lesson. ***** The Nucleus The nucleus at the center of an atom contains all of the protons and neutrons in the atom. The nucleus is very small, with a diameter that is roughly 100,000 times smaller than the effective diameter of most atoms, yet the nucleus contains all of the atom’s positive charge, and nearly all of its mass. Because the nucleus contains nearly all of the atom’s mass in a tiny volume, it is extremely dense. Outside of the nucleus, nearly all of the volume of an atom is occupied by its electrons. Because electrons have low mass but occupy a large volume compared to the nucleus, the region occupied by the electrons has a very low density. In terms of mass, an atom is mostly empty space. However, an electron has a charge that is equal in magnitude (though opposite) to that of the much more massive proton. Types of Nuclei Only certain combinations of protons and neutrons form a nucleus that is stable. In a nuclear reaction (such as radioactive decay or in a nuclear reactor), if a combination of protons and neutrons is formed that is unstable, the nucleus will decay. The combinations of protons and neutrons found in nuclei can be divided into three types. • Stable: Stable nuclei are combinations of protons and neutrons that do not change in a planetary environment such as Earth over many billions of years. • Radioactive: Radioactive nuclei are somewhat stable. Once formed, they can exist for a time on Earth (from a few seconds to several billion years), but they fall apart (decay) at a constant, characteristic rate. • Unstable: In nuclear reactions, if combinations of protons and neutrons form that are unstable, they decay within a few seconds. Nuclei that exist in the earth’s crust include all of the stable nuclei plus some radioactive nuclei. For all atoms with between one and 82 protons (except for technetium (43) and promethium (61)), at least one stable nucleus exists. Atoms with 83 to 92 protons can also be found in the earth’s crust, but all are radioactive. Atoms with 93 or more protons exist on earth only when they are created in nuclear reactions (such as in nuclear reactors). Radioactive atoms comprise a very small percentage of the matter found on earth. Over 99.99% of the earth’s atoms have nuclei that are stable. The nuclei in those stable atoms have not changed since the atoms came together to form the earth billions of years ago. © 2011 www.ChemReview.Net v.n4 Page OS 106 Module 6 – Atoms, Ions, and Periodicity Terminology Protons and neutrons are termed nucleons because they are found in the nucleus. A combination of a certain number of protons and neutrons is called a nuclide. A group of nuclides that have the same number of protons (so they are all the same atom) but differing numbers of neutrons are called the isotopes of the atom. Stable Nuclei Some atoms have only one stable nuclide; other atoms have as many as 10 stable isotopes. Example: All atoms with 17 protons are called chlorine. Only two chlorine nuclei are stable: those with • 17 protons and 18 neutrons, and • 17 protons and 20 neutrons. Nuclei that have 17 protons and other numbers of neutrons can be made in nuclear reactions, but in all of those combinations, within a few seconds, the nucleus decays by emitting a particle from the nucleus. Nuclide Symbols Each nuclide can be assigned a mass number which is the sum of its number of protons and neutrons. Mass Number of a nucleus = p+ + n0 = Protons + Neutrons Example: A nucleus with 2 p+ and 2 n0 is helium with a mass number of 4. A nuclide can be identified in two ways, • by its number of protons and number of neutrons, or • by its nuclide symbol (also termed its isotope symbol). A nuclide symbol has two required parts: the atom symbol and the mass number. The mass number is written as a superscript in front of the atom symbol. Example: The two stable isotopes of chlorine can be represented as • 17 protons + 18 neutrons or as 35Cl (named chlorine-35); and • 17 protons + 20 neutrons or as 37Cl (chlorine-37). Knowing one representation for the composition of a nucleus, you need to be able to write the other. Using a table of atoms, atom symbols, and atomic numbers that can be found at the end of these lessons, try these questions. Q1. A nuclide with 6 protons and 8 neutrons would have what nuclide symbol? ***** © 2011 www.ChemReview.Net v.n4 Page OS 107 Module 6 – Atoms, Ions, and Periodicity A1. Atoms with 6 protons are always named carbon, symbol C. The mass number of this nuclide is 6 protons + 8 neutrons = 14 . This isotope of carbon, used in “radiocarbon dating,” is named carbon-14 and its symbol is written 14C . Try another. Q2. How many protons and neutrons would be found in 20Ne ? ***** A2. All atoms called neon contain 10 protons. The mass number 20 is the total number of protons plus neutrons, so neon-20 contains 10 protons and 10 neutrons. Nuclide symbols may also include the nuclear charge written in front of and below the atom symbol. This is called the A-Z notation for a nuclide, illustrated at the right. A is the symbol for mass number and Z is the symbol for nuclear charge. In atoms, Z is also the number of protons in the nucleus. 37 Cl 17 Nuclide symbols can also be used to identify subatomic particles (particles smaller than atoms), and in those cases the nuclear charge may be zero or negative. However, Z values are not required to identify an atom, since the Z repeats what the symbol identifies: the number of protons in the nucleus. Practice A: Consult a table of atoms or periodic table to fill in the blanks below. 1. 7 Neutrons Atomic Number 6 Protons 6 Mass Number Nuclide Symbol Nuclide Name 7 Iodine-131 235U 2 4 2. Which nuclides in Problem 1 must be radioactive? Why? © 2011 www.ChemReview.Net v.n4 Page OS 108 Module 6 – Atoms, Ions, and Periodicity ANSWERS Practice A 1. Protons Neutrons Atomic Number Mass Number Nuclide Symbol Nuclide Name 6 6 6 12 12 C Carbon-12 7 7 7 14 14 N Nitrogen-14 53 78 53 131 131I Iodine-131 92 143 92 235 235U Uranium-235 2 2 2 4 4He Helium-4 2. Uranium must be radioactive, because no nuclei with more than 82 protons are stable. The Mass of Nuclides The mass of a single nuclide is usually measured in atomic mass units, abbreviated amu. One amu is equal to 1.66 x 10─24 grams. Protons and neutrons have essentially the same mass, and both are much heavier than electrons. The mass of • a proton is just over 1.0 amu (1.007 amu), • a neutron is just over 1.0 amu (1.009 amu), and • an electron is 1/1837th of an amu. Based on those masses, you might expect that the mass of a 35Cl atom would be just over 35.0 amu, since it is composed of 17 protons, 18 neutrons (~17amu + ~18 amu = ~35 amu), plus 18 electrons with small mass. In fact, for neutral atoms of 35Cl, the actual mass is 34.97 amu, slightly lighter than the combined mass of its protons, neutrons, and electrons. Why do the masses of the three subatomic particles not add exactly to the mass of the atom? When protons and neutrons combine to form nuclei, a small amount of mass is either converted to, or created from, energy. This change is the relationship postulated by Einstein: Energy gained or lost = mass lost or gained times the speed of light squared Which in equation form is written: E = mc2 In nuclear reactions, if a small amount of mass is lost, a very large amount of energy is created. In forming nuclei, however, because the gain or loss in mass is relatively small, the mass of a nuclide or atom in amu’s will approximately (but not exactly) equal its mass number. The sum of the protons and neutrons of a nuclide roughly equals its mass in amu. © 2011 www.ChemReview.Net v.n4 Page OS 109 Module 6 – Atoms, Ions, and Periodicity The Average Mass of Atoms (Atomic Mass) In addition, for most atoms (those not formed by radioactive decay), one kind of atom may have several stable isotopes, but in visible-sized samples of that atom found in substances on earth, the percentage of each isotope is identical. For this reason, when dealing with visible amounts of most atoms will have the same average mass in any matter found on earth. This average mass of an atom, called its atomic mass, can be calculated from the weighted average of the mass of its isotopes. For example, in all samples of chlorine, the ratio of the nuclides is very close to 3 nuclides with a mass of 35.0 amu for every one with a mass of 37.0 amu. The average mass is therefore the average of ( 35.0 + 35.0 + 35.0 + 37.0 ) amu . Find the average mass of these particles. ***** Average = (Sum of values)/(number of values) = ***** = (35.0 + 35.0 + 35.0 + 37.0) amu/4 = 142/4 = 35.5 amu Precise Calculation of Weighted Averages For most atoms, the characteristic atomic mass cannot be calculated precisely using the method above, because the ratios between the isotopes are not as simple and exact as the “3 to one” ratio that is very close to true for chlorine. However, for all atoms, if we know a precise mass of the isotopes and the percent that is each isotope in samples of the atoms, we calculate a precise atomic mass using this general formula for the weighted average: (1.00)(average value for mixture) = (fraction)1(value)1 + (fraction)2(value)2 + … (1) In this equation, the fraction of a component in a mixture can be calculated by dividing, for any uniform sample, the number of particles that are the component by the total number of particles in the sample. In mathematical terms, this means • • fraction = part/total , which will be a number less than one (0. XXX…); the sum of the fractions in the mixture must add up to 1.00 . If a percentage is known, the fraction is simply the percentage divided by 100. Another way to write equation (1) is (1.00)(average value for mixture) =∑ (fraction for component)(value of component) where ∑ represents a summation. © 2011 www.ChemReview.Net v.n4 Page OS 110 (2) Module 6 – Atoms, Ions, and Periodicity Precise Calculation of Atomic Mass Since the atomic mass of an atom is the weighted average of the atomic masses of its isotopes, the equation for atomic mass can be written as atomic mass of atom = ∑ (isotope fraction)(isotope mass) or as atomic mass = (isotope fraction)1(isotope mass)1 + (isotope fraction)2(isotope mass)2 + … Let’s apply this formula to chlorine atoms again, but this time using measurements that are more precise than in the example above. Q. All samples of chlorine atoms in the earth’s crust contain • 75.78% atoms that have 35Cl nuclei with a mass of 34.97 amu; and • 24.22% atoms that have 37Cl nuclei with a mass of 36.97 amu. a. What fraction of chlorine atoms are 37Cl ? b. Calculate the atomic mass of chlorine atoms. ***** a. The fraction is the percentage divided by 100. 37Cl fraction = 0.2422 Try part b. ***** The atomic mass of an atom is a weighted average. Substituting into the equation, atomic mass Cl = (0.7578)(34.97 amu) + (__________)(____________) = _________ amu Fill in the blanks, then check your answer by looking up the atomic mass of chlorine online. ***** atomic mass Cl = (0.7578)(34.97 amu) + (0.2422)(36.97 amu) = ___________ amu ***** © 2011 www.ChemReview.Net v.n4 Page OS 111 Module 6 – Atoms, Ions, and Periodicity = 26.500 amu + 8.946 amu = 35.454 = 35.45 amu = average mass for a chlorine atom (SF: carry extra sf until the final step; when adding, round to highest place with doubt.) No single atom of chlorine will have this average mass, but in visible amounts of substances containing chlorine, the chlorine atoms have this average mass. Use of this average mass (atomic mass) will simplify calculations involving mass. The numeric value for the atomic mass in amu that is found in tables is also the average mass of the atom in “grams per mole.” The number 6.022 x 1023, called one mole, is a value that simplifies the math when converting between grams of a substance and its number of particles. Practice B 1. Silver has two stable isotopes: 107Ag (106.91 amu) and 109Ag (108.90 amu). Assuming that 51.8% of naturally occurring silver is silver-107, a. calculate the atomic mass of Ag. b. Compare your answer to the value listed for silver in the table at the end of these lessons. c. What would be the atomic mass of Ag in grams per mole? ANSWERS Practice B 1a. Since there are only two Ag isotopes, 109Ag must be 48.2%. (0.518)(106.91 amu) + (0.482)(108.90 amu) = (55.38 + 52.49) amu = 107.87 = 107.9 amu 1b. It should match. 1c. 107.9 g/mole © 2011 www.ChemReview.Net v.n4 (value for amu = value for g/mole) Page OS 112 Module 6 – Atoms, Ions, and Periodicity Isotopes and Chemistry The rules and the reactions for “standard chemistry” are very different from those of nuclear chemistry. For example, • chemical reactions can release substantial amounts of energy, such as seen in the burning of fuels or in conventional explosives. Nuclear reactions, however, can involve much larger amounts of energy, as in stars or nuclear weapons. • An important rule in chemical reactions is that atoms can neither be created nor destroyed. In nuclear reactions, atoms are often created and destroyed. Because the rules are very different, a clear distinction must be made between chemistry and nuclear chemistry. By convention, it is assumed that the rules that are cited as part of “chemistry” refer to processes that do not involve changes in nuclei (unless nuclear chemistry is specified). Processes that change the composition of the nucleus are termed nuclear reactions which by definition are not chemical reactions. The good news is that, except for experiments in nuclear chemistry, because all isotopes of an atom nearly always have the same chemical behavior, and because in visible amounts of substances, a given atom always has the same average mass, we can ignore the fact that atoms have isotopes as we investigate nearly all chemical reactions and processes. We will return to the differences among isotopes when we consider nuclear chemistry, which includes reactions such as radioactive decay, fission, and fusion. Practice C Fill in the blanks below. Protons Neutrons Electrons Atomic Number 144 88 Mass Number Nuclide Symbol 90 Pu2+ 148 206Pb 78 0 Protons Neutrons Ion Symbol H+ Electrons Atomic Number Mass Number 15 16 © 2011 www.ChemReview.Net v.n4 H─ 90Sr 36 10 Ion Symbol 3H 11 Nuclide Symbol 23 18 Page OS 113 Module 6 – Atoms, Ions, and Periodicity ANSWERS Practice C Protons Neutrons Electrons Atomic Number Mass Number Nuclide Symbol Ion Symbol 90 144 88 90 234 234Th Th2+ 94 148 92 94 242 242Pu Pu2+ 82 124 78 82 206 206Pb Pb4+ 1 0 0 1 1 1H H+ 1 2 2 1 3 3H H─ 38 52 36 38 90 90Sr Sr2+ 11 12 10 11 23 23Na Na+ 15 16 18 15 31 31 P P3─ Lesson 6C: Elements, Compounds, and Formulas Pretest: Use the list of atoms on the next-to-last page of these lessons. With a perfect pretest score, skip to Lesson 6D. 1. In this list: A. H2O B. Cl2 C. Au D. S8 E. CO2 F. Co G. H2SO4 a. Which formulas represent elements? b. Which formulas represent a substance without ionic or covalent bonds? c. Which formulas represent substances that are diatomic? 2. Write the number of oxygen atoms present in each of these compounds. a. Co(OH)2 b. CH3COOH c. Al2(SO4)3 3. Write the total number of atoms in each of the compounds in question 2. ***** ANSWERS Pretest: 1a. B, C, D, F 1b. C, F © 2011 www.ChemReview.Net v.n4 1c. B 2a. 2 2b. 2 2c. 12 3a. 5 3b. 8 3c. 17 Page OS 114 Module 6 – Atoms, Ions, and Periodicity Substances The definitions below are general and highly simplified, but they will give us a starting point for discussing the particles encountered in chemistry. 1. A substance contains one kind of chemical particle: all of the neutral units have the same number and kind of atoms, chemically bonded in the same manner and geometry. Chemical formulas can be used to represent a substance. A mixture is a combination of two or more substances. Substances have characteristic properties: their melting points, color, and densities are some of the properties that will be the same for a substance no matter what steps are taken to form the substance. These properties can help in identifying the substance. A mixture is a combination of two or more substances. 2. In a substance, if the smallest particles that can be separated from each other relatively easily are neutral particles with two or more atoms, the particles are called molecules. If a substance consists of charged particles that can separate from each other if they dissolve in water, the separated particles are called ions, and the smallest electrically neutral combination of ions is called a formula unit. 3. Elements are substances that contain only one kind of atom. Each atom has an elemental state. Its elemental state is the substance formula and phase (solid, liquid, or gas) that is the most stable form that exists at room temperature and pressure. The basic particles for some elements, termed the monatomic elements, are individual atoms. The chemical formulas for monatomic elements are written as one instance of the atom’s formula, reflecting the fact that the basic unit is a single atom that is not bonded to other atoms. . For example, the basic particles of the noble gases (helium, neon, argon, krypton, xenon, and radon) are single atoms. Therefore, the formulas for these elements are written as He for helium, Ne for neon, etc. At typical room temperature and pressure, some substances that are elements consist of two or more atoms of the same kind that are chemically bonded to form a new larger unit. Cl2 and S8 are all formulas for elements because they are substances that contain only one kind of atom, and those formulas represent the most stable form in which a collection of those atoms will exist at normal room temperature and pressure. 4. Bonds are forces that hold particles together. The diatomic elements consist of two atoms (di- means two), and their chemical formulas reflect the fact that each unit contains 2 atoms. In chemical formulas, a subscript written after a symbol represents the number of that kind of atom or ion that is bonded within the particle. For example, the elemental forms of oxygen, nitrogen, and chlorine are all diatomic. Their chemical formulas are O2, N2, and Cl2. © 2011 www.ChemReview.Net v.n4 Page OS 115 Module 6 – Atoms, Ions, and Periodicity Polyatomic elements are neutral molecules that contain 2 or more atoms, but only one kind of atom. For example, the elemental formula for sulfur is S8, indicating that it exists as eight atoms bonded together. In their elemental state, over 70% of the atoms that can be found in the earths’ crust are metals. Metals have a more complex structure than simple monatomic or polyatomic elements, but metal formulas are represented by single atoms, such as Ag for silver, and Al for aluminum. 5. A compound is a substance that consists of two or more different atoms that are chemically bonded. While there are just over 100 elements, there are millions of known compounds. In a given compound, the ratio of the atoms is always the same, and is shown by their formulas. H2O, NaCl, and H2SO4 are all formulas for compounds, because they contain two or more different kinds of atoms. Compounds can be classified as either ionic or covalent, depending on their bonds. 6. The basic particles for covalent compounds (also known as molecular compounds) are molecules. Molecules are held together by covalent bonds. In a covalent bond, electrons are shared between two neighboring atoms. Covalent bonds can be single bonds (involving 2 shared electrons), double bonds (4 shared electrons), or triple bonds (6 shared electrons). Covalent bonds hold atoms at predictable angles within the molecule. 7. Molecular formulas use atomic symbols and subscripts to represent the number and kind of atoms covalently bonded together to form a single molecule. • Water is a molecule that consists of two hydrogen atoms and one oxygen atom, represented by the molecular formula H2O. In chemical formulas, when there is no subscript written after a symbol, the subscript is understood to be one. • Carbon dioxide is composed of molecules that each consist of two oxygen atoms and one carbon atom. Its molecular formula is written as CO2. Practice A: Use the atoms table at the end of these lessons or in a textbook to answer these questions. Answers are at the end of the lesson. 1. Identify each sample sketched below as an element, compound, or mixture. Different atoms are indicated by different shades, and individual particles are separated for clarity. a. a. _______________ © 2011 www.ChemReview.Net v.n4 b. c. b._________________ c. ______________ Page OS 116 Module 6 – Atoms, Ions, and Periodicity 2. Label the following formulas as representing elements or compounds. a. Ne b. H2O c. NaCl d. S8 e. C6H12O6 3. Which of these formulas contain chemical bonds? a. H2 b. CO c. NH3 d. He 4. In problems 2 and 3, which formulas represent a. Diatomic elements? b. Monatomic elements? c. 4 atoms? ANSWERS Practice A: 1. a. Compound b. Element c. Mixture 2. 2a and 2d are elements because they have one kind of atom. The rest are compounds because they have more than one kind of atom. 3. 3a, 3b, and 3c have bonds, because they have more than one atom. It takes bonds to hold two or more atoms together in particles. 4. 3a, H2, is the only diatomic element. 5. 2a and 3d are the only monatomic elements. 6. 3d, NH3 is the only formula with 4 atoms. More Vocabulary 8. Structural formulas can be used to represent chemical particles that are held together by covalent bonds. These formulas show the atoms present plus information about their positions within the particle. O __ H / H At the left is a structural formula for water. It shows that the oxygen atom is found in the middle of the molecule, and that water has two directional covalent single bonds and a bent shape. The structural formula for carbon dioxide, CO2 , is O=C=O . Carbon dioxide has two double bonds, and the molecule is linear in shape with the carbon atom in the middle. We generally write structural formulas when knowing the shape of the molecule is important, but we write the more compact molecular formulas when it is not. © 2011 www.ChemReview.Net v.n4 Page OS 117 Module 6 – Atoms, Ions, and Periodicity 9. Often, chemical formulas are written as a mixture of structural and molecular formulas. For example, • The formula for ethyl alcohol can be written as C2H6O or as CH3CH2OH. The shorter formula, however, is also the molecular formula of dimethyl ether, which is usually written CH3OCH3 to show that the O is found in the middle in the ether, rather than toward one end as in the alcohol. Ethyl alcohol and dimethyl ether have the same number and kind of atoms, but the different arrangement of the atoms give the molecules very different properties. To predict chemical behavior, we often need to know a formula with structural information. In such cases, we write the longer formulas like those above. 10. Ionic compounds are substances consisting of a collection of positive and negative ions. Ions can be monatomic (single atoms with a charge) or polyatomic (a group of covalently bonded atoms that have an unequal number of protons and electrons). An ionic bond is the electrostatic attraction between oppositely charged ions. 11. Ionic formulas represent the ratio and kind of ions present in an ionic compound. The ions in an ionic compound are always present in a ratio that guarantees overall electrical neutrality. A formula unit is defined as the smallest combination of ions for which the sum of the electrical charges is zero. Parentheses are used to indicate more than 1 polyatomic ion. Chemical formulas for ionic compounds show the atom ratios in a single neutral formula unit. • Table salt consists of a 1:1 ratio of positively charged sodium ions (formula Na+) and negatively charged chloride ions (Cl─). The formal name of table salt is sodium chloride, and its ionic formula is written as NaCl. The formula unit NaCl contains 2 ions. • 12. Parentheses are used if a formula unit contains more than 1 polyatomic ion. For example, copper(II) nitrate is an ionic compound composed of one monatomic Cu+2 ion for every two polyatomic NO3─ ions. The ionic formula is written as Cu(NO3)2. When you write formulas, be careful to distinguish between upper- and lower-case letter combinations such as CS and Cs, Co and CO, NO and No. • Co(OH)2 has 1 cobalt atom, 2 oxygen atoms, and 2 hydrogen atoms. • CH3COOH has 2 carbon, 4 hydrogen, and 2 oxygen atoms. To summarize, although molecules of covalent substances and formula units of ionic compounds have different types of bonds, all compound formulas refer to a single, overall electrically neutral unit of a substance. © 2011 www.ChemReview.Net v.n4 Page OS 118 Module 6 – Atoms, Ions, and Periodicity Practice B: Use the table of atoms at the end of these lessons or in a textbook to answer these questions. 1. Write the number of oxygen atoms in each of these compounds. a. Al(OH)3 b. C2H5COOH c. Co3(PO4)2 2. Write the total number of atoms for each of the compounds in question 1. 3. Try two of these, then check your answers. Need more practice? Do a few more. Name each atom, and write the total number of those atoms, in each of the following formulas. a. HCOOH b. CoCO3 c. (NH4)3PO4 d. Pb(C2H5)4 4. If you need additional practice, do the pretest at the beginning of Lesson 6C. ANSWERS Practice B 1a. 3 oxygen atoms 3. a. 2 hydrogen 1 carbon 2 oxygen 1b. 2 1c. 8 2a. 7 total atoms b. 1 cobalt 1 carbon 3 oxygen c. 3 nitrogen 12 hydrogen 1 phosphorus 4 oxygen 2b. 11 2c. 13 d. 1 lead 8 carbon 20 hydrogen ***** © 2011 www.ChemReview.Net v.n4 Page OS 119 Module 6 – Atoms, Ions, and Periodicity Lesson 6D: The Periodic Table Pretest: If you think you know this topic, try the last letter of each numbered question at the end of this lesson. If you get those right, you may skip this lesson. ***** Patterns of Chemical Behavior Learning the behavior of over 100 different atoms would be a formidable task. Fortunately, the atoms can be organized into families. The chemical behavior of one atom in a family will help to predict the behavior of other atoms in the family. The grouping of atoms into families results in the periodic table. To build the table, the atoms are arranged in rows across (also called periods) in order of the number of protons in each atom. This order usually, but not always, matches the order of the increasing atomic mass of the atoms. At certain points, the chemical properties of the atoms begin to repeat, somewhat like the octaves on a musical scale. In the periodic table, under most graphic designs, when a noble gas atom is reached, it marks the end of a row. The next atom, with one more proton, starts a new row of the table. This convention places the atoms into vertical columns (called families or groups) with the noble gases in the last column on the right. Within each column, the atoms tend to have similar chemical behavior. Some Families in the Periodic Table The noble gases (He, Ne, Ar, Kr, Xe, Rn) are monatomic (composed of single atoms) as elements. They can be liquefied by lowering temperature and/or increasing pressure, but in their elemental state at room temperature and pressure, all are gases. These atoms are termed noble because they are chemically “content” with their status as single atoms: these atoms rarely bond with other atoms or each other. The alkali metals (Li, Na, K, Rb, Cs, Fr) are in column one (also called group 1A) of the periodic table, at the far left. As elements, all are soft, shiny metals that tend to react with many substances, including the water vapor present in air. In chemical reactions, neutral alkali metal atoms tend to lose an electron to become a 1+ ion. This ion has the same number of electrons as the noble gas that has one fewer protons. Once an alkali metal atom forms a 1+ ion, it becomes quite stable. Most chemical reactions do not change its +1 charge. The halogens (F, Cl, Br, I, and At) are in column 7 (group 7A) just to the left of the noble gas column. As neutral elements at room temperature, halogen atoms are stable only when the atoms bond to form diatomic molecules; F2, Cl2, Br2, I2, and At2. Like alkali metals, the halogens are very reactive. In reactions, neutral halogen atoms tend to gain one electron to become a halide ion with a 1─ charge. Halogen atoms can also share electrons with neutral atoms of other nonmetals. Shared electrons result in a covalent bond. © 2011 www.ChemReview.Net v.n4 Page OS 120 Module 6 – Atoms, Ions, and Periodicity Hydrogen is often placed in column one of the table, and the reactions of hydrogen are often like those of the alkali metals. However, other hydrogen reactions are like those of the halogens. Hydrogen is probably best portrayed as a unique family of one that can have characteristics of both alkali metals and halogens. The main group elements are those found in the tall column blocks on both sides of the table. They are termed either groups 1, 2, and 13 to 18, or groups 1A, 2A, and 3A-8A, depending on the version of the periodic table that you are using. The transition metals are in the “middle dip” of the periodic table, in groups 3-12 or the “B” groups. There are 10 atoms in each row of the transition metals. The inner transition atoms include the 14 lanthanides (or rare earth metals) in the 6th row and the 14 actinides in the 7th row. These atoms are usually listed below the rest of the periodic table in order to display a table that fits easily on a chart or page. ***** Predicting Behavior The following table summarizes the general characteristics of the atoms in the columns of the periodic table. The positions of the column numbers, family names, and likely ion charges should be memorized. Group 1A 2A Family Name Alkali Metals Alkaline Earth Metals 1+ 2+ Monatomic ion charge 3B or 3 2B 12 3A 4A 5A 6A 3+ (or 1+) 3─ 2─ 8A Halogens Transition Metals 7A Noble Gases 1─ None For example: Cesium (Cs) is in column one of the periodic table. Based on this placement, it can be predicted to • • behave like other alkali metal atoms; and exist as a Cs+ ion in compounds. Practice A: Use a copy of the periodic table and your memorized knowledge about the table (first learn the rules, then do the practice) to answer these. 1. Describe the location in the periodic table of the a. Transition metals b. Rare earth metals 2. Add a charge to these symbols to show the ion that a single atom of these elements tends to form. a. Br b. Ra © 2011 www.ChemReview.Net v.n4 c. Cs d. Te Page OS 121 Module 6 – Atoms, Ions, and Periodicity ANSWERS Practice A: 1a. The 10 columns in the middle dip. 2 a. Br─ b. Ra2+ 1b. The two rows usually shown below the main table. c. Cs+ d. Te2─ Metals, Metalloids, and Nonmetals The elements in the periodic table can be divided into metals, metalloids (also called semimetals), and nonmetals. Metalloids Many periodic tables include a thick line, like a staircase, as shown in the section of the periodic table below. This line separates the metal and nonmetal atoms. The six atoms bordering the line in bold below are the metalloids. They have chemical behavior that is in-between that of the metals and the nonmetals. Unless you are allowed to use a periodic table that has the staircase and identifies the metalloids on tests, you should memorize the location of the staircase and the 6 metalloids. If you memorize how the staircase looks at boron (B), the rest of the staircase is simplified. Some textbooks include polonium (Po) as a metalloid, others do not. C N O Si P S Cl Ar Ge As Se Br Kr Sb Te I Xe (Po) B (H) F He Ne At Rn Nonmetals At the right are the 18 nonmetals. The nonmetals must be memorized: H, C, N, O, P, S, Se, plus the 5 halogens and 6 noble gases. Note the shape of their positions. The nonmetals are all to the right of the staircase and to the right of the metalloids. All atoms in the last two columns are nonmetals. (H) C He N O F Ne P S Cl Ar Se Br Kr I Xe At Rn Note also that hydrogen, although it is often shown in column one, is considered to be a nonmetal. Hydrogen has unique properties, but it most often behaves as a nonmetal. © 2011 www.ChemReview.Net v.n4 Page OS 122 Module 6 – Atoms, Ions, and Periodicity Metals The metals are all of the elements to the left of the thick line and the six metalloids, including the inner transition elements that are usually listed below the rest of the chart. In their electrically neutral, elemental form, metal atoms behave as metals: all are substances that are shiny and conduct electricity. Neutral metal atoms tend to react to form positive ions in compounds. Metal ions do not look or behave like metals. Of the over 100 elements, over 75 percent are metals. To learn the atoms that are metals, memorize the 6 metalloids and 18 nonmetals. All of the remaining elements are metals. Practice B: Use a copy of the periodic table and your memorized knowledge about the columns of the table to answer these. 1. How many atoms are non-metals? 2. Without consulting a periodic table, add the metal/nonmetal dividing line to the portion of the periodic table at the right, then circle the metalloid atoms. (H) He B C N O F Ne Al Si P S Cl Ar Zn Ga Ge As Se Br Kr Cd In Sn Sb Te I Xe Hg Tl Pb Bi Po At Rn ANSWERS Practice B: 1. 18 2. See table in lesson. ***** © 2011 www.ChemReview.Net v.n4 Page OS 123 Module 6 – Atoms, Ions, and Periodicity Lesson 6E: A Flashcard Review System Previous Flashcards At this point, you may have a sizeable stack of flashcards, and soon we will add more. Before going further, let’s organize the cards. Try this system. A. Separate your existing flashcards into 4 stacks. 1-Daily: Those you have not yet “practiced until correct” for 3 days. 2-End of Chapter/Quiz: Those you have done for more than 3 days. Run again before your next quiz on this material. 3-Test: Those you have done 4 or more times. Run again before starting the practice problems for your next major test. 4-Final Exam Review: Those you have retired until the final. B. Add cards with those 4 labels to the top of each stack. Rubber-band each stack. You may want to carry the daily pack with you for practice during down time. Module 6 Flashcards If you have had a previous course in chemistry, you may recall much of the material in Module 6 after a brief review. Other points may be less familiar, and the material in Module 6 will need to be firmly in memory for the rest of the course. For points that are not firmly in memory, make the flashcards. For the sample cards below: cover the answers, put a check next to those which you can answer correctly and quickly. Make a flashcard if the answer is not automatic. Run your new cards for several days in a row. Run the two-way cards in both directions. Run the cards again before your next quiz, test, and final exam. For Lesson 6A One-way cards (with notch at top right): Back Side -- Answers Like charges Repel Unlike Charges Attract The particles in a nucleus = protons and neutrons Subatomic particle with lowest mass electron Subatomic particles with charge protons and electrons Mass of a proton in amu 1.0 amu Protons minus electrons = Charge on particle Number of protons determines Atom name, symbol, and atomic number Particles gained and lost in chemical reactions electrons Zero charge on an atom means # protons = # electrons Negative ions have More electrons than protons Subatomic particles with mass of 1.0 amu protons and neutrons © 2011 www.ChemReview.Net v.n4 Page OS 124 Module 6 – Atoms, Ions, and Periodicity Two-way cards (without notch): ion A particle with electrical charge Protons plus Neutrons = Mass Number = For Lesson 6B One-way cards (with notch) Back Side -- Answers To calculate the average atomic mass of an atom, use ∑ (isotope fraction)(isotope mass) Same # of p+, different # of n0 isotopes Different nuclides with same chemical behavior = isotopes Two-way cards (without notch): 1 proton and 2 neutrons = ? nuclide symbol 3H = contains what particles? Protons plus neutrons approximately equals Mass of nuclide in amu approx. equals For Lesson 6C Two-way cards (without notch): Define a Substance All particles have same chemical formula A Mixture 2 or more substances Molecule Neutral, independent particles with two or more atoms Structural Formula Shows atoms and positions in a particle Elements Stable neutral substances with one kind of atom Compounds Neutral substances with more than one kind of atom Bonds Forces holding atoms together For Lesson 6D One-way cards (with notch) Back Side -- Answers Family that rarely bonds to other atoms noble gases Lightest non-metal Hydrogen (H) Lightest metalloid Boron (B) Number of non-metal elements 18 Two-way cards (without notch): Position of alkali metals First column, except hydrogen Position of rare earths (lanthanides) First row below body of table Position of transition metals In dip between tall columns 2 and 3 Tend to form 1─ ions Ions formed by halogen atoms Family forms 1─ns Ions formed by alkali metals © 2011 www.ChemReview.Net v.n4 Page OS 125 Module 6 – Atoms, Ions, and Periodicity Family forms +2 ions Column 2 – Alkaline earth metals Name for halogen atoms with a ─1 charge Halide ions ***** Lesson 6F: Atoms Project – Part 4 The following frequently encountered atoms have symbols based on their Latin names. See if these are not in memory in both directions. Two-way cards (without notch): Two-way cards (without notch): copper Cu iron Fe tin Sn lead Pb mercury Hg silver Ag gold Au sodium Na potassium K antimony Sb ##### © 2011 www.ChemReview.Net v.n4 Page OS 126 Module 7 – Writing Names and Formulas Module 7 – Writing Names and Formulas Lesson 7A: Naming Elements and Covalent Compounds Pretest: If you think you know this topic, try the last letter of each question in Practice A and Practice B. If you get those right, skip the lesson. ***** Systems for Naming Substances Chemical substances are identified by both a unique name and a chemical formula. For names and formulas that both identify and differentiate substances, a system for writing formulas and names is required. 1. Some compounds have names that are non-systematic but familiar: Water (H2O) and ammonia (NH3) are examples. 2. Historically, chemical substances have been divided into two broad categories. Compounds containing carbon and hydrogen are studied in organic chemistry, which has its own system for naming compounds. All other substances are part of inorganic chemistry, which is the focus of most first-year courses. 3. Different types of inorganic substances have different naming systems. We will begin with the rules for naming elements, ions, and binary covalent compounds. Naming Elements An element is a stable, electrically neutral substance that contains of only one kind of atom. The name of an element is simply the name of its atoms. Examples • The element comprised of neutral atoms with 20 protons is called calcium. Calcium is a metal, and the formulas of metals are written as if they are monatomic elements. The formula for the element calcium is therefore written as Ca. • Neutral oxygen atoms, at room temperature, are stable when they exist in diatomic molecules. For the element oxygen, the formula is O2. • At room temperature, sulfur atoms tend to form molecules with 8 bonded atoms. The formula for the elemental form of sulfur is S8. Note that for elements, the formula may distinguish between monatomic, diatomic, or polyatomic structures, but the name does not. This is only an issue for a few of the elements, but for the millions of chemical compounds, a more systematic nomenclature (naming system) is needed. © 2011 www.ChemReview.Net v.n4 Page OS 127 Module 7 – Writing Names and Formulas Compounds In a compound, there is more than one kind of atom. Most compounds can be classified as either ionic or covalent. Covalent compounds are molecules containing non-metal atoms that are bonded together by electrons shared between the atoms. The attractive forces (bonds) within covalent molecules are strong compared to the attractions between the molecules. Solids at room temperature may be ionic or covalent compounds, but compounds that are gases or liquids at room temperature are nearly always covalent compounds. At room temperature, ionic compounds are nearly always solids. Ionic compounds are composed of an array of ions bonded strongly by electrostatic attractions. Types of Bonds Chemical bonds can be separated into several categories, including metallic bonds found in metals and the hydrogen bonds that are relatively weak but play an important role in the structure of proteins and DNA. However, the two types of bonds that we encounter most often in substances are the relatively strong bonds termed covalent and ionic bonds. Ionic and covalent compounds have different naming systems. To name a compound we must first identify it as ionic or covalent. To make that distinction, we must first identify the types of bonds in the compound. Use these rules. 1. In covalent bonds, electrons are shared between two atoms. 2. In ionic bonds, an atom (or group of atoms) has lost one or more electrons (compared to its electrically neutral form), and another atom (or group of atoms) has gained one or more electrons. The loss and gain of electrons results in charged particles (ions). The ions are bonded by the attraction of their opposite charges. 3. The following rules will predict whether a bond is ionic or covalent in most cases. • A bond between two nonmetal atoms is usually a covalent bond. • A bond between a metal and a nonmetal atom is usually an ionic bond. 4. To identify the type of bond, begin by asking: are both atoms non-metals? If so, the bond is covalent. The non-metals are shown at the right. Recall that hydrogen is classified as a nonmetal, and that all atoms in the last two columns are nonmetals. (H) C He N O F Ne P S Cl Ar Se Br Kr I Xe At Rn The six noble gases rarely bond. The remaining 12 nonmetal atoms nearly always form covalent bonds when they bond with each other. 5. Ask: is one of the atoms in the bond a metal and the other a non-metal? If so, the bond is nearly always ionic in character. © 2011 www.ChemReview.Net v.n4 Page OS 128 Module 7 – Writing Names and Formulas Using those rules and a periodic table, answer these questions. Q. Predict whether the following bonds will likely be ionic or covalent. 1. C─H 2. Na─C 3. N─Cl 4. K─Cl ***** Answers 1. C─H Both are non-metals, so predict this to be a covalent bond. 2. Na─C A metal and a non-metal atom; predict an ionic bond. 3. N─Cl Both are non-metals; predict a covalent bond. 4. K─Cl A metal and non-metal; predict a ionic bond. ***** Types of Compounds 1. If a compound contains all covalent bonds, it is classified as a covalent compound. 2. If a compound has one or more ionic bonds, even if it also has many covalent bonds, it will tend to have ionic behavior and is classified as an ionic compound. These rules mean that in most cases, • a compound with all nonmetal atoms is a covalent compound. • a compound that combines metal and nonmetal atoms is an ionic compound. Q. Using those rules and a periodic table, label these compounds as ionic or covalent. 1. NaCl 2. CH4 3. Cl2 4. HCl ***** Answers 1. NaCl Na is a metal, Cl is non-metal, compound is ionic. 2. CH4 Both atoms are non-metals; compound is covalent. 3. Cl2 Both atoms are non-metals; compound is covalent. 4. HCl Both atoms are non-metals; compound is covalent. The above general rules do not cover all types of bonds and compounds, and there are many exceptions. However, these rules give us a starting point for both naming compounds and writing formulas. © 2011 www.ChemReview.Net v.n4 Page OS 129 Module 7 – Writing Names and Formulas Covalent Compounds The 12 nonmetals that tend to bond are a small percentage of the more than 100 atoms. However, because • covalent bonds tend to be strong, • the nonmetal atoms are relatively abundant on our planet, and • the molecules in living systems are based on a nonmetal (carbon), a substantial percentage of the compounds studied in chemistry are covalent compounds. Practice A For the problems below, use the type of periodic table that you are permitted to view on tests in your course. You should not need to consult the metal versus nonmetal charts found in these lessons, since they should be committed to memory. 1. Label these bonds as ionic or covalent. a. Na─I b. C─Cl c. S─O d. Ca─F e. C─H f. K─Br 2. Label these compounds as ionic or covalent. a. CF4 b. KCl c. CaH2 d. H2O e. NF3 f. CH3ONa ANSWERS Practice A 1. a. Na─I Ionic b. C─Cl Covalent c. S─O Covalent d. Ca─F Ionic e. C─H Covalent f. K─Br Ionic b. KCl Ionic c. CaH2 Ionic e. NF3 Covalent f. CH3ONa Ionic 2. a. CF4 Covalent d. H2O Covalent (All of the ionic compounds contain a metal atom.) Naming Binary Covalent Compounds Binary covalent compounds contain two different nonmetals (bi- means two). The naming of binary compounds uses the atom names or the root of the atom names. Binary covalent compounds that include hydrogen are usually given “common names” such as methane, water, and ammonia, or follow special rules for acid compounds. For the 11 remaining non-metals that bond, the roots are C=carb-, N=nitr-, O=ox-, F=fluor-, P=phosph-, S=sulf-, C=chlor-, Se=selen-, Br=brom-, I=iod-, and At=astat-. Not all of those roots are “regular,” but their use will become intuitive with practice. © 2011 www.ChemReview.Net v.n4 Page OS 130 Module 7 – Writing Names and Formulas For compounds composed of two different nonmetal atoms, the rules for naming are: 1. The name contains two words. The format is prefix-atom name then prefix-root-ide . Example: The name of N2Cl4 is dinitrogen tetrachloride. 2. This rule takes precedence over the rules below. For covalent compounds that contain • O atoms, the second word is prefix-oxide. • H atoms, the compound usually has a name that does not follow these rules. 3. The first word contains the name of the atom (of the two atom symbols in the formula) that is in a column farther to the left in the periodic table. If the two atoms are in the same column, the lower atom is named first. 4. The second word contains the root of the second atom name, with the suffix –ide added. 5. The number of atoms of each kind is represented by a Greek prefix. mono- = 1 atom. (In the first word, mono- is left off and assumed if no prefix is given. Mono- is included if it applies to the second word.) di- = 2 atoms penta- = 5 atoms octa- = 8 atoms tri- = 3 atoms hexa- = 6 atoms nona- = 9 atoms tetra- = 4 atoms hepta- = 7 atoms deca- = 10 atoms If an o or a at the end of a prefix is followed by a first letter of an atom or root that is a vowel, the o or a in the prefix is sometimes omitted (both inclusion and omission of the o and a are allowed, and you may see such names both ways). Using a periodic table and the above rules, try the following. Q1. What is the name of CS2? ***** A1. Carbon is in the column farther to the left in the periodic table, so carbon is the atom in the first word. For one atom, mono- is omitted if it applies to the first word. The name’s first word is simply carbon. For the second word, sulfur becomes sulfide. Since there are two sulfur atoms, the name of the compound is carbon disulfide. Q2. What is the name of the combination of four fluorine and two nitrogen atoms? ***** © 2011 www.ChemReview.Net v.n4 Page OS 131 Module 7 – Writing Names and Formulas A2. Nitrogen is in the column more to the left in the periodic table, so the first word contains nitrogen. Since there are two nitrogen atoms, add the prefix di-. For the second word, the root –ide is fluoride, and the prefix for four atoms is tetra-. The name for the compound is dinitrogen tetrafluoride. Flashcards Cover the answers below, then check those which you can answer correctly and quickly. When done, make flashcards for the others (see the steps in Lesson 2C). Run the new cards for several days in a row, then add them to the previous flashcards for quiz and test review. One-way cards (with notch) Back Side -- Answers The formula for elemental oxygen O2 A bond between a metal and nonmetal is Usually ionic A bond between two nonmetals is Usually covalent A covalent compound has Shared electrons and only covalent bonds An ionic compound has One or more ionic bonds A compound with all nonmetal atoms is usually A covalent compound Compounds with metal atoms are Ionic compounds Binary Covalent Name Format Prefix-atom prefix-root-ide Binary Covalent Name First Left column first, lower if in same column Two-way cards (without notch): Formula for ammonia = ? Name of NH3 = ? Formula for carbon monoxide = ? Name of CO = ? Formula for dinitrogen tetrachloride = ? Name of N2Cl4 = ? Practice B Learn the rules, practice needed flashcards, then try every other problem. Wait a day, run the cards again, then try the remaining problems. 1. Write the name for these combinations of nonmetals. a. Two sulfurs and one silicon. b. Three chlorine and one iodine. c. One oxygen and two chlorines. d. One bromine and one iodine 2. Name these covalent compounds. a. SCl2 b. PI3 © 2011 www.ChemReview.Net v.n4 c. SO2 d. NO Page OS 132 Module 7 – Writing Names and Formulas 3. Nonmetals often form several stable oxide combinations, including the combinations below. Name that compound! a. Five oxygen and two nitrogen c. NO2 d. b. 10 oxygen and four phosphorus N2 O e. SO3 f. Cl2O7 ANSWERS Practice B 1. a. Silicon disulfide b. Iodine trichloride (if in same column, name lower first) c. Dichlorine monoxide (oxygen is always last, drop last o in mono-) 2. a. Sulfur dichloride b. Phosphorus triiodide 3. a. Dinitrogen pentoxide (or pentaoxide) d. Dinitrogen monoxide c. Sulfur dioxide d. Iodine monobromide d. Nitrogen monoxide b. tetraphosphorus decaoxide e. Sulfur trioxide c. Nitrogen dioxide f. Dichlorine heptaoxide (or heptoxide). ***** © 2011 www.ChemReview.Net v.n4 Page OS 133 Module 7 – Writing Names and Formulas Lesson 7B: Naming Ions Pretest: If you think you know this topic, try several problems at the end of this lesson. If you complete them all correctly, you may skip the lesson. ***** Ions Ionic compounds are combinations of ions: particles with an electrical charge. In most first-year chemistry courses you will be asked to memorize the names and symbols for about 50 frequently encountered ions. This task is simplified by the patterns for ion charges that are found in the periodic table. Learning these rules and patterns will help you to speak the language of chemistry. Categories of Ions 1. All ions are either positive or negative. • A positive ion is termed a cation (pronounced KAT-eye-un). The charges on positive ions can be 1+, 2+, 3+, or 4+. • A negative ion is termed an anion (pronounced ANN-eye-un). The charges on negative ions can be 1─, 2─, or 3─. 2. All ions are either monatomic or polyatomic. • A monatomic ion is a particle that is one atom with a charge. Examples: • Na+, Al3+, Cl─, and S2─. A polyatomic ion is a particle that has two or more covalently bonded atoms and an overall electric charge. Examples: OH─, Hg 2+, NH +, and SO 2─. 2 4 4 Ions of Hydrogen Hydrogen has unique characteristics. It is classified as a nonmetal, and in many of its compounds hydrogen bonds covalently. However, in compounds classified as acids, one or more hydrogens form H+ ions when the compound is dissolved in water. In addition, when bonded to metal atoms, hydrogen behaves as an anion: the hydride ion (H─). The Structure and Charge of Metal Ions More than 70% of the atoms in the periodic table are classified as metals. • Geologically, in the earth’s crust, most metals are found as metal ions. Exceptions to the “metals are found as ions” rule include the coinage metals: copper and silver, which may be found geologically both as ions or in their metallic, elemental form, and gold, which is always found in nature as a metal. • In chemical reactions, neutral metal atoms tend to lose electrons to form positive ions. • In compounds that contain both metal and nonmetal atoms, the metal atoms nearly always behave as ions with a positive charge of 1+, 2+, 3+, or 4+. © 2011 www.ChemReview.Net v.n4 Page OS 134 Module 7 – Writing Names and Formulas • With the exception of mercurous (Hg22+) ion, all frequently encountered metal ions are monatomic: the ions are single metal atoms that have lost one or more electrons. Examples of metal ions are Na+, Mg2+, Al3+, and Sn4+. All metals form at least one stable monatomic ion. Some frequently encountered metals form two stable monatomic ions. In many cases, the charge (or possible charges) on a monatomic metal ion can be predicted from the position of the metal in the periodic table. In first-year chemistry, when you are asked to predict the charge on a monatomic metal atom, you will nearly always be allowed to consult a periodic table. Use a periodic table when learning the following rules for the charges on metal ions. Metal Ions With One Charge Metals in the first two columns of the periodic table form only one stable monatomic ion. The charge on that ion is easy to predict. • All metals in column one (the alkali metals) form only one stable ion: a single atom with a 1+ charge: Li+, Na+, K+, Rb+, Cs+, and Fr+. • All metals in column two form only one stable ion: a single atom with a 2+ charge: Be2+, Mg2+, Ca2+, Sr2+, Ba2+, and Ra2+. The charges on metal ions in the remainder of the periodic table are more difficult to predict. Additional rules for predicting ion charge will be learned when electron configuration is studied later in your course. In order to solve problems initially, most courses require that the possible charges on certain metals to the right of column 2 be memorized. The rules below will help with that process. Most metals to the right of the first two columns form two or more stable ions, but some form only one. The following rule should be memorized. • Metals to the right of the first two columns that form only one stable ion include Ag+, Zn2+, and Al3+. For help in remembering this group, note the position of these metals in the periodic table. Naming Metal Ions How a metal ion is named depends on whether the metal forms only one ion or forms two or more ions. 1. If a metal forms only one stable ion, the ion name is the atom name. Examples: Na+ is a sodium ion. Al3+ is an aluminum ion. © 2011 www.ChemReview.Net v.n4 Page OS 135 Module 7 – Writing Names and Formulas This rule applies to • metal ions in columns one and two, plus • the additional three metal ions listed above, plus • additional ions that may be studied later in chemistry. 2. For metals that form two different positive ions, the systematic name (or modern name) of the ion is the atom name followed by a roman numeral in parentheses that states the ion’s positive charge. Examples: Fe2+ is named iron(II) and Fe3+ is named iron(III) ion. 3. Metals that form two different positive ions and were “known to the ancients” also have common names for their multiple ions. In common names, the lower charged ion uses the Latin root of the atom name plus the suffix –ous. The higher-charged ion uses the Latin root plus the suffix –ic. For metal ions, the systematic (roman numeral) names are preferred, but the common (latin-based) names are often encountered. For the following 5 metals, you need to know the charges the two ions that each metal tends to form. Other metals form more than one ion, but these 5 are the most frequently encountered. Ion Symbol Systematic Ion Name Common Ion Name Cu+ Cu2+ copper(I) cuprous copper(II) cupric Fe 2 + Fe 3 + iron(II) ferrous iron(III) ferric Sn2+ Sn4+ tin(II) stannous tin(IV) stannic Hg22+ mercury(I) mercurous Hg2+ Pb2+ mercury(II) mercuric lead(II) plumbous Pb4+ lead(IV) plumbic Note the exceptional name and structure of the mercury(I) ion. Mercury(I) is the only frequently encountered metal ion that is polyatomic: it has the structure of a diatomic ion with a 2+ charge. It is given the name mercury(I) matching the format of other metal ions, in part because it behaves in many reactions as if it is two loosely bonded +1 ions. © 2011 www.ChemReview.Net v.n4 Page OS 136 Module 7 – Writing Names and Formulas When to Include Roman Numerals In Systematic Names When naming metal ions, the general rule is: • Add the (roman numeral) for ions of metal atoms that form more than one ion; • Do not use (roman numerals) in ion names for metals that can form only one stable ion. Those include ions of atoms in the first two columns, plus Ag+, Zn2+, and Al3+. Summary: Metal Ion Rules • All metal ions are positive. Except for Hg22+, nearly all metal ions are monatomic. • In column one, all atoms tend to form 1+ ions. • In column two, all atoms tend to form 2+ ions. • If a metal forms only one ion, the ion name is the atom name. • If a metal forms more than one ion, the systematic ion name is the atom name followed by a roman numeral in parentheses showing the positive charge of the ion. • For the metals to the right of column 2, metals form only one monatomic ion include Ag+, Zn2+, and Al3+. For naming purposes, assume that other metals form more than one ion and the ( ) is needed in the name. Flashcards: Using the flashcard steps in Lesson 2C, make cards for any of these that you cannot answer from memory. One-way cards (with notch) Back Side -- Answers cation A positive ion anion A negative ion Monatomic ion One atom with a charge Polyatomic ion 2 or more bonded atoms with an overall charge All metal ions (except mercurous) are Monatomic – contain only one atom The charge on a metal ion is always Positive Column one ions have what charge? +1 Column two ions have what charge? +2 When is () in an ion name needed? In systematic names, if the metal forms more than one kind of positive ion Columns 1 and 2, plus Ag+, Zn2+, and Al3+ In systematic names, which ions do not need (roman numerals) to show their charge? 5 metals that form 2 ions, and charges on each Cu+, Cu2+, Fe2+, Fe3+, Sn2+, Sn4+, Hg 2+, Hg2+, Pb2+, Pb4+ 2 © 2011 www.ChemReview.Net v.n4 Page OS 137 Module 7 – Writing Names and Formulas Practice A: Run the flashcards above until you can do them all. Then use a periodic table and do the problems below. 1. Add a charge to show the symbol for the stable ion that these atoms form. a. Ba b. Al c. Rb d. Na e. Zn f. Ag 2. Write the symbols for these ions. a. Cadmium ion b. Lithium ion c. Hydride ion d. Calcium ion 3. Which ions in Problems 1 and 2 are anions? 4. Write the name and symbol for a polyatomic metal ion often encountered. 5. Fill in the blanks. Ion Symbol Systematic Ion Name Common Ion Name Stannic Cupric Iron(III) Copper(I) Fe 2 + ANSWERS Practice A 1. a. Ba2+ b. Al3+ c. H─ c. Rb+ d. Na+ f. Ag+ 3. Only the hydride ion (H─). 2. a. Cd2+ b. L i+ 5. Ion Symbol Systematic Ion Name Common Name Sn4+ tin(IV) stannic Cu2+ copper(II) cupric F e 3+ iron(III) ferric Cu+ copper(I) cuprous Fe 2 + iron(II) ferrous © 2011 www.ChemReview.Net v.n4 d. Ca2+ e. Zn2+ 4. Hg22+ Page OS 138 Module 7 – Writing Names and Formulas Monatomic Anions Nine monatomic anions are often encountered in first-year chemistry. Their names and symbols should be memorized. • One is H─ (hydride). • Four are halides: fluoride, chloride, bromide, and iodide (F─, Cl─, Br─, and I─). Two are in tall column 6A: oxide (O2─) and sulfide (S2─). • Two are in tall column 5A: nitride (N3─), and phosphide (P3─). • For monatomic anions, the name is the root of the atom name followed by -ide. For monatomic ions, the position of the atom in the periodic table predicts the charge. Group 1A 2A Family Name Alkali Metals Alkaline Earth Metals 1+ 2+ Charge on Monatomic ion 3A 3+ (or 1+) 5A 6A 7A 8A N Family Transition Metals 4A O Family Halogens Noble Gases 3─ 2─ 1─ None Polyatomic Ions A polyatomic ion is a particle that has two or more atoms held together by covalent bonds and has an overall electrical charge. In polyatomic ions, the total number of protons and electrons in the particle is not equal. An example of a polyatomic ion is the hydroxide ion, OH─. One way to form this ion is to start with a neutral water molecule H—O—H, which has 1+8+1 = 10 protons and 10 balancing electrons, and take away an H+ ion (which has one proton and no electrons). The result is a particle composed of two atoms with a total of 9 protons and 10 electrons. Overall, the particle has a negative charge. The negative charge behaves as if it is attached to the oxygen. A structural formula for the hydroxide ion is H—O─ Polyatomic ions will be considered in more detail when studying the three-dimensional structure of particles. At this point, our interest is the ratios in which ions combine. For that purpose, it may help to think of a monatomic ion as a charge that has one atom attached, and a polyatomic ion as a charge with several atoms attached. Polyatomic Cations Three polyatomic cations with names and symbols that should be memorized are the NH4+ (ammonium), H3O+ (hydronium), and Hg22+ (mercury(I) or mercurous) ions. © 2011 www.ChemReview.Net v.n4 Page OS 139 Module 7 – Writing Names and Formulas Oxyanions Polyatomic ions with negative charges that contain non-metals and oxygen are termed oxyanions. Oxyanions are often part of a series of ions that has one common atom and the same charge, but different numbers of oxygen atoms. Example: Nitrate ion = NO3─ , nitrite ion = NO2 The names and symbols for most oxyanions can be determined from the following rules. Oxyanion Naming System 1. When an atom has two oxyanions that have the same charge, the ion with more oxygens is named root-ate , and the ion with one fewer oxygen atoms is root-ite. Example: Sulfate is SO42─ . Sulfite is SO32─ 2. If an atom has more than two oxyanions with the same charge, the • per–root–ate ion has X oxygen atoms: • root-ate ion has one fewer oxygens; • root-ite ion has 2 fewer oxygens; • hypo-root-ite ion has 3 fewer oxygens. Example: Memorize that the ClO4─ ion is named perchlorate. Then, • ClO3─ is chlorate; • ClO2─ is chlorite; • ClO─ is hypochlorite. A way to simplify naming these ions is to memorize the name and formula for the ion in the series that has the most oxygens, then write out the rest by logic as needed. With practice, this naming process will become automatic. Learning the Ion Names and Formulas In most courses, you will be asked to memorize the names and formulas for a list of frequently encountered ions. Being able to automatically convert between the names and formulas for ions is essential when solving complex problems in the remainder of your course. Spaced practice of the following flashcards will move into memory what you need to know. You may want to use a unique card color to identify these as the ion cards, or add the word ion for clarity after each ion name. Your course may not require that you know the “latin” names for the metal ions. If so, omit those names. Check that you can answer in both directions. Omit making flashcards for names and formulas that you already know well in both directions. © 2011 www.ChemReview.Net v.n4 Page OS 140 Module 7 – Writing Names and Formulas For a large number of new flashcards, allow yourself several days of practice. In the beginning, writing the pairs and saying the answers will speed your progress. Two-way cards (without notch): Two-way cards (without notch): CH3COO─ acetate ion Cu+ cuprous/copper(I) ion CN─ OH─ cyanide ion cupric/copper(II) ion hydroxide ion Cu2+ Fe2+ NO3─ nitrate ion Fe3+ ferric/iron(III) ion MnO4─ permanganate ion Sn2+ stannous/tin(II) ion C O3 2 ─ carbonate ion Sn4+ stannic/tin(IV) ion HCO3─ hydrogen carbonate ion Hg22+ mercurous or mercury(I) ion CrO42─ chromate ion Hg2+ mercuric or mercury(II) Cr2O72─ dichromate ion O2 ─ oxide ion P O4 3 ─ phosphate ion S2 ─ sulfide ion SO42─ sulfate ion N3─ nitride ion SO32─ sulfite ion P3─ phosphide ion Na+ sodium ion ClO4─ perchlorate ion K+ potassium ion ClO3─ chlorate ion Al3+ aluminum ion ClO2─ chlorite ion F─ Cl─ fluoride ion ClO─ H+ hypochlorite ion hydride ion magnesium ion chloride ion ferrous/iron(II) ion hydrogen ion Br─ I─ bromide ion iodide ion H─ Mg2+ Ca 2 + calcium ion NH4+ ammonium ion Ba 2 + barium ion H3O+ hydronium ion © 2011 www.ChemReview.Net v.n4 Page OS 141 Module 7 – Writing Names and Formulas Practice B: Learn the rules and run the flashcards for the ion names and symbols in the section above, then try these problems. 1. In this chart of ions, from memory, add charges, names, and ion formulas. Symbol Ion name C O3 acetate radium MnO4 CN silver CrO4 hydroxide K Al dichromate ClO4 P O4 nitrate sulfate sodium sulfide F Ba 2. Circle the polyatomic ion symbols in the left column of Problem 1 above. 3. If NO3─ is a nitrate ion, what is the symbol for a nitrite ion? 4. Complete this table for the series of oxyanions containing bromine. Ion name Ion Symbol Per_______________ ______________ _________________________ BrO3─ Bromite _________________ Hypo________________ __________________ © 2011 www.ChemReview.Net v.n4 Page OS 142 Module 7 – Writing Names and Formulas ANSWERS Practice B Symbol Ion name C O3 2 ─ carbonate CH3COO─ acetate Ra2+ radium CN─ cyanide MnO4─ permanganate Ag+ silver CrO42─ chromate OH─ hydroxide K+ potassium Al3+ aluminum Cr2O72─ dichromate ClO4─ perchlorate P O 4 3─ phosphate NO3─ nitrate SO42─ sulfate Na+ sodium S2─ sulfide F─ 1,2. fluoride B a 2+ barium 3. NO2─ 4. Ion name Ion Symbol Perbromate BrO4─ Bromate BrO3─ Bromite BrO2─ Hypobromite BrO─ ***** © 2011 www.ChemReview.Net v.n4 Page OS 143 Module 7 – Writing Names and Formulas Lesson 7C: Names and Formulas for Ionic Compounds Pretest: Using a periodic table, if you get these right 100%, you may skip the lesson. 1. Name Pb3(PO4)2 2. Write formulas for a. tin(IV) chlorate b. radium nitrate 3. Write a balanced equation for ammonium phosphate separating into its ions. ***** ANSWERS Pretest: 1. Lead(II) phosphate 3. (NH4)3PO4 2a. Sn(ClO3)4 2b. Ra(NO3)2 3 NH4+ + 1 PO43─ Ionic Compounds: Fundamentals If ions have opposite charges, they attract. Ionic compounds are solids at room temperature that contain positive ions (cations) combined with negative ions (anions). The composition of an ionic compound can be expressed in three ways. • By a name; • As a solid formula; • Example: ammonium phosphate Example: (NH4)3PO4 And as balanced, separated ions. Example: 3 NH4+ + 1 PO43─ As a part of solving many problems, given one type of identification, you will need to write the other two. Ionic compounds can initially be confusing because their names and solid formulas do not clearly identify the charges on the ions. To solve problems that involve ionic compounds, a key step will be to translate the name or solid formula into the separated-ions format that shows the formulas of the ions, including their charges, and their ratio in the compound. In an ionic compound, the ions must be present in a ratio that balances the charges and results in electrical neutrality. © 2011 www.ChemReview.Net v.n4 Page OS 144 Module 7 – Writing Names and Formulas Balancing Separated Ions It is a fundamental law of the universe that if matter has an electrical charge, it will tend to arrange and/or react in ways that balance that charge, so that the overall number of positive and negative charges in a collection of particles is the same. In the case of charged particles that are ions, the result is this rule: In any combination of ions, whether in solids, melted, or dissolved in water, the total charges on the ions must balance: the total number of positive charges must equal the total number of negative charges, so that the overall net charge is zero. When ions combine, only one ratio will result in electrical neutrality. In problems, you will often need to determine that ratio. When determining the names and formulas for ionic compounds, the first steps are • Write the separated-ion symbols, then • Write coefficients in front of each symbol that make the total number of positive charges equal the total number of negative charges. Let’s learn to do this with an example. Q. Find the ratio that balances the charges when S2─ and Na+ combine. In your notebook, apply the following steps, then check your answer below. Step 1. Write the two ion symbols separated by a + sign. Writing the cation (positive ion) first is preferred. Leave space to write a number in front of each ion symbol. Step 2. Coefficients are numbers written in front of ion or particle symbols. In all formulas for ionic compounds, (Coefficient times charge of cation) must balance (coefficient times charge of anion). When you are balancing, you cannot change the symbol or the charge of an ion. When balancing, the only change that you can make, and the one change that you must make, is to write whole-number coefficients in front of the particle symbols that balance the charges. Step 3. Reduce the coefficients to the lowest whole-number ratios. ***** © 2011 www.ChemReview.Net v.n4 Page OS 145 Module 7 – Writing Names and Formulas Answer Step 1. Step 2. Na+ + S2─ 2 Na+ + 1 S2─ This is the separated-ions formula. There must be two sodium ions for every one sulfide ion. Why? For the charges, (2 times 1+ = 2+) balances (1 times 2─ = 2─). In ion combinations, the ions are always present in ratios that result in a balance of the positive and negative charges. Step 3. 2 and 1 are the lowest whole-number ratios. Only one set of coefficient ratios will balance the charges. Those coefficients show the ratios in which the ions must be found in the compound. Try another. Cover the answer below, then try this question using the steps above. Q. Add coefficients so that the charges balance: ___ Al3+ + ___ SO42─ ***** Answer: One way to determine the coefficients is to make the number of charges on each ion equal to the coefficient of the other ion. 2 Al3+ + 3 SO42─ For these ions, (2 times +3 = +6) balances (3 times ─2 = ─6). In an ionic compound, the total positives and total negatives must balance. However, when balancing charge when using this method, you often must adjust the coefficients so that the final coefficients are the lowest whole-number ratios. Try Q. Add proper coefficients: ____ Ba2+ + ____ SO42─ ***** Answer If balancing produces a ratio of 2 Ba2+ + 2 SO42─ , write the final coefficients as 1 Ba2+ + 1 SO42─ To write solid formulas, you will need the lowest whole-number ratio that results in electrical neutrality. © 2011 www.ChemReview.Net v.n4 Page OS 146 Module 7 – Writing Names and Formulas Practice A: Add lowest-whole-number coefficients to make these separated ions balanced for charge. Start with the odd numbers; save the evens for your next practice session. After every two, check your answers at the end of the lesson. 1. ____ Na+ + ____ Cl─ 4. NH4+ + 2. Mg2+ + SO42─ 5. Al3+ + 3. Cl─ Al3+ 6. HPO42─ + + CH3COO─ PO43─ In3+ ANSWERS Practice A 1. 1 Na+ + 1 Cl─ 2. 1 Mg2+ + 1 SO 2─ 4 3. 3 Cl─ + 1 Al3+ 4. 1 NH4+ + 1 CH3COO─ 5. 1 Al3+ + 1 PO43─ 6. 3 HPO42─ + 2 In3+ Writing the Separated Ions from Names To write the separated ions from the name of an ionic compound, follow these steps. Step 1: The first word in an ionic compound name is always the positive ion. Write: Step 2: positive ion symbol + negative ion symbol Add the lowest-whole-number coefficients that balance the charges. Try those steps on this problem. Q. Write a balanced separated-ions formula for aluminum carbonate. ***** © 2011 www.ChemReview.Net v.n4 Page OS 147 Module 7 – Writing Names and Formulas Answer: Step 1: Aluminum carbonate Step 2: Aluminum carbonate Al3+ + CO32─ 2 Al3+ + 3 CO32─ The separated-ions formula shows clearly what the name does not: in aluminum carbonate, there must be 2 aluminum ions for every 3 carbonate ions. When writing separated ions, write the charges high, any subscripts low, and the coefficients at the same level as the atom symbols. Practice B If you have not done so today, run your ion flashcards. Then write balanced separated-ion formulas for the ionic compounds below. You may use a periodic table, but otherwise write the ion formulas from memory. Do odds now, evens later. Check answers as you go. 1. Sodium hydroxide 2. Rubidium sulfite 3. Lead(II) phosphate 4. Calcium perchlorate ANSWERS Practice B 1. Sodium hydroxide 2. Rubidium sulfite 1 Na+ + 1 OH─ 3. Lead(II) phosphate 2 Rb+ + 1 SO32─ 4. Calcium perchlorate 3 Pb2+ + 2 PO43─ 1 Ca2+ + 2 ClO4─ Writing Solid Formulas From Names In ionic solid formulas, charges are hidden, but charges must balance. The key to writing a correct solid formula is to write the balanced separated-ions first, so that you can see and balance the charges. © 2011 www.ChemReview.Net v.n4 Page OS 148 Module 7 – Writing Names and Formulas To write a solid formula from the name of an ionic compound, use these steps. 1. Based on the name, write the separated ions. Add lowest whole number coefficients to balance charge. Then, to the right, draw an arrow . 2. After the , write the two ion symbols, positive ion first, with a small space between them. Include any subscripts that are part of the ion symbol, but leave out charges and coefficients. 3. For the symbols after the arrow, put parentheses () around a polyatomic ion if its coefficient in the separated-ions formula on the left is more than 1. 4. Add subscripts after each symbol on the right. The subscript must be the same as the coefficient in front of that ion in the separated-ions formula. Omit subscripts of 1. For polyatomic ions, write the coefficients as subscripts outside and after the parentheses. In your notebook, apply those steps to this example. Q. Write the solid formula for potassium sulfide. ***** Answer 2 K+ + 1 S2─ 1: Write the separated-ions formula first. For potassium sulfide: 2: Re-write the symbols without coefficients or charges. 2 K+ + 1 S2─ 3: Since both K and S ions are monatomic, add no parentheses. 4: The K coefficient becomes its solid formula subscript: 2 K+ + 1 S2─ KS K2S The sulfide subscript of one is omitted as understood. The solid formula for potassium sulfide is K2S. Try another : Q. Write the solid formula for magnesium phosphate. ***** © 2011 www.ChemReview.Net v.n4 Page OS 149 Module 7 – Writing Names and Formulas Answer 1: Write the balanced separated ions. Magnesium phosphate 3 Mg2+ + 2 PO43─ 2: Write symbols without coefficients or charges. 3 Mg2+ + 2 PO43─ Mg PO4 3: Since Mg2+ is monatomic (just one atom), it is not placed in parentheses. Phosphate is both polyatomic and we need more than 1, so add ( ) . Mg (PO4) 4: Each ion’s coefficient on the left becomes its solid subscript on the right. Mg3(PO4)2 Mg3(PO4)2 is the solid formula for magnesium phosphate. Recite the 3-P’s rule until it is committed to memory. When writing ionic-solid formulas: Put parentheses around polyatomic ions -- if you need more than one. Practice C: As you go, check the answers at the end of the lesson. You may want to do half of the lettered parts today and the rest during your next study session. 1. Circle the polyatomic ions. a. Na+ b. NH4+ c. CH3COO─ d. Hg2+ e. OH─ 2. When do you need parentheses? Write the rule from memory. 3. Balance these separated ions for charge, then write solid formulas. a. K+ + b. NH4+ + CrO42─ c. SO32─ + d. Sn4+ + S2─ Sr2+ SO42─ 4. From these names, write the separated-ions formula, then the solid formula. a. Ammonium sulfite b. Potassium permanganate c. Calcium hypochlorite d. Sodium hydrogen carbonate © 2011 www.ChemReview.Net v.n4 Page OS 150 Module 7 – Writing Names and Formulas 5. Write the solid formula. a. Tin(II) fluoride b. Calcium hydroxide c. Radium acetate ANSWERS Practice C 1. The polyatomic ions: b. NH4+ c. CH3COO─ e. OH─ 2. For ionic solid formulas, put parentheses around polyatomic ions IF you need more than one. SrSO 3c. 1 SO 2─ + 1 Sr2+ 3a. 2 K+ + 1 CrO 2─ K CrO 4 3b. 2 NH4+ + 1 S2─ 2 4 3 Sn(SO4)2 3d. 1 Sn4+ + 2 SO42─ Ca(ClO)2 4c. 1 Ca2+ + 2 OCl─ (NH4)2S 4a. 2 NH4+ + 1 SO32─ (NH4)2SO3 4b. 1 K+ + 1 MnO4─ 3 4d. 1 Na+ + 1 HCO3─ KMnO4 NaHCO3 5. Write balanced, separated ions first. a. Tin(II) fluoride 1 Sn2+ + 2 F─ b. Calcium hydroxide c. Radium acetate SnF2 1 Ca2+ + 2 OH─ 1 Ra2+ + 2 CH3COO─ © 2011 www.ChemReview.Net v.n4 Ca(OH)2 Ra(CH3COO)2 Page OS 151 Module 7 – Writing Names and Formulas Writing Separated Ions From Solid Formulas When placed in water, all ionic solids dissolve to some extent. The ions that dissolve separate and move about independently in the solution. This dissolving process can be represented by a chemical equation that has a solid on the left and the separated ions on the right. For example, when solid sodium phosphate dissolves in water, the equation is Na3PO4(s) H2O 3 Na+(aq) + 1 PO43─(aq) The (s) is an abbreviation for the solid state. The (aq) is an abbreviation for the aqueous state, which means “dissolved in water.” When a compound separates into ions that can move about freely, the reaction is termed dissociation. If the reactant is an ionic solid, the ions are already present in the solid: dissolving simply allows the ions to separate, move about, collide, and potentially react with other particles. Every equation representing ion separation must balance atoms, balance charge, and result in correct formulas for the ions that are actually found in the solution. In equations for an ionic solid separating into its ions, some subscripts in the solid formula become coefficients in the separated ions, but others do not. In the equation above, the subscript 3 became a coefficient, but the subscripts 1 and 4 did not. To correctly separate solid formulas into ions, you must be able to recognize the ions inside the solid formula. That’s why the frequently encountered ion names and formulas must be memorized. Cover the answer below, try this example, then check the answer for tips that will make this process easier. When needed, read a part of the answer for a hint, then try again. Q. Write the equation for the ionic solid Cu2CO3 separating into its ions. ***** Answer: Follow these steps in going from a solid formula to separated ions. Step 1: Decide the negative ion’s charge and coefficient first. The first ion in a solid formula is always the positive ion, but many metal ions can have two possible positive charges. Most negative ions only have one likely charge, and that charge is often needed to identify the positive ion’s charge, so we usually add the charge to the negative ion first. In Cu2CO3, the negative ion is CO3, which always has a 2─ charge. This step temporarily splits the solid formula into © 2011 www.ChemReview.Net v.n4 Cu2 and 1 CO32─ . Page OS 152 Module 7 – Writing Names and Formulas Step 2: Decide the positive ion’s charge and coefficients. Given Cu2 and CO32─ , the positive ion or ions must include 2 copper atoms and must have a total 2+ charge to balance the charge of CO 2─. 3 So Cu2 , in the separated-ions formula, must be either 1 Cu22+ or 2 Cu+ . Both possibilities balance atoms and charge. Which is correct? Recall that All metal ions are monatomic (except Hg22+ (mercury(I) ion)). This means that Cu+ must be the ion that forms, since Cu22+ is polyatomic. Because most metal ions are monatomic, a solid formula with a metal ion will separate MXAnion X M+? + Anion (unless the metal ion is Hg22+). You also know that Cu+ is the copper(I) ion that was previously memorized because it is frequently encountered. Both rules lead us to predict that the equation for ion separation is Cu2CO3 2 Cu+ + 1 CO32─ Copper can also be a Cu2+ ion, but in the formula above, there is only one carbonate, and carbonate always has a 2─ charge. Two Cu2+ ions cannot balance the single carbonate. Step 3: Check: Make sure that the charges balance. Make sure that the number of atoms of each kind is the same on both sides. The equation must also make sense going backwards, from the separated to the solid formula. Try another. Q2. Write the equation for the ionic solid (NH4)2S dissolving to form ions. ***** Answer • In a solid formula, parentheses are placed around polyatomic ions. When you write the separated ions, a subscript after parentheses always becomes the polyatomic ion’s coefficient. You would therefore split the formula • (NH4)2S Assign the charges that these ions prefer. (NH4)2S © 2011 www.ChemReview.Net v.n4 2 NH4 + 1 S 2 NH4+ + 1 S2─ Page OS 153 Module 7 – Writing Names and Formulas • Check: In the separated formula, do the charges balance? Going backwards, do the separated ions combine to give the solid formula? Keep up your practice, for 15-20 minutes a day, with your ion name and formula flashcards (Lesson 7B). Identifying ions without consulting a table will be most helpful when solving the problems that lie ahead. Practice D If you have not done so today, run your ion flashcards in both directions, then try these. To take advantage of the “spacing effect”(Lesson 2C), do half of the lettered parts below today, and the rest during your next study session. 1. Finish balancing by adding ions, coefficients, and charges. a. PbCO3 b. Hg2SO4 Pb + 1 CO32─ Hg2 + 2. Write equations for these ionic solids separating into ions. a. KOH b. CuCH3COO c. Fe3(PO4)2 d. Ag2CO3 e. NH4OBr f. Mg(OH)2 Answers are after Practice E below. © 2011 www.ChemReview.Net v.n4 Page OS 154 Module 7 – Writing Names and Formulas Naming Ionic Compounds From a solid or a separated-ions formula, writing the name is easy. Step 1: Write the separated-ions formula. Step 2: Write the name of the positive ion, then the name of the negative ion. That’s it! In ionic compounds, the name ignores the number of ions inside. Simply name the ions in the compound, with the positive ion first. Try this problem. Q. Name K2CO3 . ***** 2 K+ + 1 CO32─ ; the name is potassium carbonate. With time, you will be able to convert solid formulas to compound names without writing the separated ions, but the only way to develop this accurate intuition is by practice. K2CO3 Practice E: If you are unsure of an answer, check it before continuing. 1. Return to Practice D and name each compound. 2. In Practice C, Problems 3 and 4, name each compound. 3. Would CBr4 be named carbon bromide or carbon tetrabromide? Why? 4. Name these ionic and covalent compounds. Try half today and half during your next study session. a. CaBr2 b. NCl3 c. NaH d. CuCl2 e. RbClO4 f. KOI g. Li3P h. PbO i. NH4BrO2 j. SO2 k. CaSO3 l. P4S3 ANSWERS © 2011 www.ChemReview.Net v.n4 Page OS 155 Module 7 – Writing Names and Formulas Practice D and E 1. a. PbCO3 b. Hg2SO4 1 Pb2+ + 1 CO32─ Part E: Lead(II) carbonate 1 Hg22+ + 1 SO42─ Mercurous sulfate or Mercury(I) sulfate 1 K+ + 1 OH─ Potassium hydroxide 1 Cu+ + 1 CH3COO─ Copper(I) acetate or cuprous acetate b. CuCH3COO 2. a. KOH c. Fe3(PO4)2 3 Fe2+ + 2 PO43─ Iron(II) phosphate or ferrous phosphate d. Ag2CO3 2 Ag+ + 1 CO32─ Silver carbonate e. NH4OBr 1 NH4+ + 1 BrO─ Ammonium hypobromite f. Mg(OH)2 1 Mg2+ + 2 OH─ Magnesium hydroxide E2. C3a. Potassium chromate C3b. Ammonium sulfide C3c. Strontium sulfite C3d. Tin(IV) sulfate E3: Carbon tetrabromide. Carbon is a nonmetal, so the compound is covalent (see Lesson 7A). Use di-, triprefixes in the names of covalent compounds. Practice recognizing the symbols of the nonmetals. E4. a. Calcium bromide b. Nitrogen trichloride c. Sodium hydride c. Copper(II) chloride or cupric chloride e. Rubidium perchlorate g. Lithium phosphide h. Lead(II) oxide i. Ammonium bromite k. Calcium sulfite f. Potassium hypoiodite j. Sulfur dioxide l. Tetraphosphorus trisulfide Flashcards: Add these to your collection. One-way cards (with notch) What must be true in all ionic substances? Numbers you add to balance separated ions To understand ionic compounds: When are parentheses needed in formulas? In separated-ion formulas, what do the coefficients tell you? Back Side -- Answers Total + charges = total ─ charges Must be electrically neutral coefficients Write the separated-ion formulas In solid formulas, put parentheses around polyatomic ions -- if you need >1 The ratio in which the ions must be present to balance atoms and charge ***** © 2011 www.ChemReview.Net v.n4 Page OS 156 Module 7 – Writing Names and Formulas Practice F: Combining Ions Worksheet Fill in the blanks. Complete half of the rows today and the rest during your next study session. Ionic Compound NAME SEPARATED Ions SOLID Formula • • • • • • • • Positive ion first • Charges balance, but don’t show • Put () around polyatomic ions IF you need >1 Name by ion names Must be two or more words Put name of + ion first Sodium chloride Charges must show Charges must balance Charges may flow Coefficients tell ratio of ions 1 Na+ + 1 Cl─ NaCl 2 A13+ + 3 SO32─ A12(SO3)3 Lithium carbonate Potassium hydroxide ___ Ag+ + ___ NO3─ ___ NH4+ + ___ SO42─ FeBr2 Fe2(SO4)3 Copper(II) chloride Tin(II) fluoride __ A13+ + __ Cr2O72─ K2CrO4 CaCO3 Aluminum phosphate © 2011 www.ChemReview.Net v.n4 Page OS 157 Module 7 – Writing Names and Formulas ANSWERS Practice F Ionic Compound NAME SEPARATED Ions SOLID Formula Sodium chloride 1 Na+ + 1 Cl─ NaCl Aluminum sulfite 2 Al3+ + 3 SO32─ Al2(SO3)3 Lithium carbonate 2 Li+ + CO32─ Li2CO3 Potassium hydroxide 1 K+ + 1 OH─ KOH Silver nitrate 1 Ag+ + 1 NO3─ AgNO3 Ammonium sulfate 2 NH4+ + 1 SO42─ (NH4)2SO4 Iron(II) bromide/Ferrous bromide 1 Fe2+ + 2 Br─ FeBr2 Iron(III) sulfate/Ferric sulfate 2 Fe3+ + 3 SO42─ Fe2(SO4)3 Copper(II) chloride 1 Cu+ + 1 Cl─ CuCl Tin(II) fluoride 1 Sn 2 + + 2 F─ SnF2 Aluminum dichromate 2 Al3+ + 3 Cr2O72─ Al2(Cr2O7)3 Potassium chromate 2 K+ + CrO42─ K2CrO4 Calcium carbonate 1 Ca2+ + 1 CO32─ CaCO3 Aluminum phosphate 1 Al3+ + 1 PO43─ AlPO4 © 2011 www.ChemReview.Net v.n4 Page OS 158 Module 7 – Writing Names and Formulas Lesson 7D: Naming Acids Pretest: If you think you know this topic, try the last two problems on the practice at the end of the lesson. If you get all of those parts right, skip this lesson. ***** Acids An acid can be defined as a substance that, when dissolved in water, forms H+ ions (there are other definitions for acids, but this is a place to start). This dissolving process can be represented by a reaction equation that has a solid, liquid, or gas on the left and the separated ions on the right. For example, when the covalent gas hydrogen chloride dissolves in water, it forms a solution of hydrochloric acid. The reaction equation is HCl(g) H2O 1 H+(aq) + 1 Cl─(aq) ( or HCl(aq) ) Recall that (aq) is an abbreviation for aqueous (dissolved in water). A hydrochloric acid solution is usually represented using the molecular formula HCl(aq), but the separated ions are a more accurate description of the behavior of an acid. The two formulas on the right are equivalent, and we will need both types when naming acids. Acid Nomenclature Because of the long history of acids in chemistry, the names follow a variety of rules. We can write a long set of rules to cover all cases, but for now it is easier to memorize a few frequently encountered name and formula combinations, then learn a set of rules that generally apply to the remaining cases. The steps to name acids: Apply these rules in order. Rule 1: Memorize the names for these acid solutions, by 2-way flashcards if needed. H2SO4(aq) is sulfuric acid, H2SO3(aq) is sulfurous acid, H3PO4(aq) is phosphoric acid, HCN is hydrocyanic acid. The combination of an H+ ion and an OH─ ion (aq) is…? Water. Rule 2: Memorize: Four acids that combine one hydrogen and one halogen atom are HCl = hydrochloric acid, HF = hydrofluoric acid, HBr = hydrobromic acid, and HI = hydroiodic acid. The next rule will apply to H+ ions combined with oxoanions: negative ions that contain oxygen. Some oxoanions occur in a series that have the same charge but decreasing numbers of oxygens. For the four-member oxoanion sequence that contain halogen atoms, the naming is XO ─ XO ─ XO─ ( where X can be the halogen Cl, Br, or I ) XO ─ 4 Perhaloate 3 haloate © 2011 www.ChemReview.Net v.n4 2 haloite hypohaloite Page OS 159 Module 7 – Writing Names and Formulas Examples: BrO─ is hypobromite ion, IO3─ is iodate ion, Some oxoanion series include just two members. Examples: NO3─ (nitrate) and NO2─ (nitrite) . Some oxoanions are not part of a series, such as CO 2─ (carbonate ion). 3 Rule 3. If an acid contains an H+ ion and an oxoanion, to name the acid: a. Write the name of the oxoanion, then cross off the suffix to form the root name. b. If the ion suffix was –ate , replace the suffix with –ic followed by the word acid. c. If the ion suffix was –ite , replace the suffix with –ous acid. Examples: For the acid H2CO3(aq) To be neutral, the acid must combine 2 H+(aq) + 1 CO32─(aq) (To understand ionic compounds, write the separated ions formula.) The negative ion CO32─ is named carbonate . The acid name for H2CO3(aq) is carbonic acid. Note that multiple H+ ions in the acid do not affect the name. For the acid HClO(aq) , By oxoanion rules, the ion ClO─ is named hypochlorite . The acid name for HClO(aq) is therefore hypochlorous acid. Q. Apply Rule 3 to name these acid solutions. a. HClO4(aq) b. HNO2(aq) ***** `a. In the acid HClO4 , the negative ion is ClO4─, named perchlorate . The name for an HClO4 solution is perchloric acid. b. In the acid HNO2 , the negative ion is NO2─, named nitrite . The name for an HNO2 solution is nitrous acid. Acid Formulas In most cases, because the H+ ion is positive, it is written first in formulas. In compounds that contain carbon and hydrogen (organic compounds), other rules are followed. For example: the solution consisting of H+ ion and CH3COO─ ion is named…? ***** © 2011 www.ChemReview.Net v.n4 Page OS 160 Module 7 – Writing Names and Formulas Acetate acetic acid , contains oxygen and is named by Rule 3 above. For this organic acid (containing carbon and hydrogen), you will see the formula written as CH3COOH or CH3CO2H or HC2H3O2 or HAc (in which Ac is an abbreviation for acetate ion and is not the atom actinium). However, most acid formulas write the acidic H’s in front. We will address additional rules for identifying acid formulas in Module 14. Practice: As always, it will improve efficiency and effectiveness if you first learn the rules, then do the practice, and save a few problems for your next study session. 1. Name these acid solutions. a. HCl b. HIO d. H3PO4 c. HNO3 2. Write molecular formulas representing aqueous solutions of these acids. a. Bromous acid b. Sulfurous acid c. Chromic acid 3. Write formulas and names for aqueous solutions containing these ions. a. H+ and MnO4─ b. H+ and SO4─ c. H+ and IO3─ 4. The formula for the arsenate ion is AsO43─. What is the name and formula for an aqueous solution of an acid composed of H+ ions and AsO43─ ions ? ANSWERS 1a. Hydrochloric acid by rule 2. 1b. Hypoiodous acid by rule 3 from hypoiodite ion. 1c. Nitric acid by rule 3 from nitrate ion. 2a. Bromous acid must include bromite ion which is BrO2─, so the acid must be HBrO2(aq) . 2b. Sulfurous acid is memorized as H2SO3(aq) . 2c. Chromic acid must come from chromate ion which is CrO42─, so the acid must be H2CrO4(aq) . 3a. The acid’s anion is permanganate , so the acid name is permanganic acid; HMnO4(aq) . 3b. The neutral molecular formula must be H2SO4(aq) which is sulfuric acid (Rule 1). 3c. The acid’s anion is iodate , so the acid name is iodic acid; HIO3(aq) . 4. To be neutral, must be 3 H+ + 1 AsO43─ 1d. Phosphoric acid by rule 1. H3AsO4(aq) . Arsenate ion is the anion in arsenic acid. ***** © 2011 www.ChemReview.Net v.n4 Page OS 161 Module 7 – Writing Names and Formulas Lesson 7E: Review Quiz For Modules 5-7 You may use a calculator and a periodic table. Work on your own paper. State answers to calculations in proper significant figures. Set a 30-minute limit, then check your answers after the Summary that follows. ***** 1. (See Lesson 5D): If there are 96,500 coulombs per mole of electrons and 1 mole = 6.02 x 1023 electrons, what is the charge in coulombs on 100. electrons? 2. (Lesson 5E): One acre is 43,560 square feet. If one foot = 0.3048 meters, 0.250 acres is how many square meters? 3. (Lesson 5F): What is the volume in mL of a metal cylinder that is 5.0 cm in diameter and 2.0 cm long? Use a calculator. Vcylinder = πr2h 4. (Lesson 6B): For a particle with atomic number 92 that contains 143 neutrons and 90 electrons, write the nuclide (isotope) symbol and then the symbol for the ion. 5. (Lesson 6B): A particle of the isotope 107Ag is an Ag+ ion. How many protons, neutrons, and electrons does the particle contain? 6. (Lesson 6B): If an atom has two isotopes with masses of 104.0 amu and 108.0 amu, and 22.0% of the atom in naturally occurring samples is the lighter isotope, what is the atom’s atomic mass? 7. (Lesson 6D): Which of these lists contains all non-metals? a. C, N, S, Na, O b. H, I, He, P, C c. F, H, Ne, Si, S d. Br, H, Al, N, C 8. (7C): Write the symbols for the ions that are combined to form these compounds. a. Ag2SO4 b. NaOH c. K2CrO4 9. (Lessons 7B-D): Write chemical formulas for these compounds. a. Sodium dichromate b. Ammonium phosphate c. Aluminum iodate d. Hydroiodic acid e. Nitrous acid f. Bromic acid 10. (Lessons 7B-D): Name these compounds. a. Br2O7 b. KClO c. NaHCO3 d. Fe2(SO3)3 e. CH3COOH f. HBrO 11. (4F, 6F): On the following table, fill in the names and symbols for the atoms in the first 3 rows and the first 2 and last 2 columns. © 2011 www.ChemReview.Net v.n4 Page OS 162 Module 7 – Writing Names and Formulas Periodic Table 1A 2A 3A 4A 5A 6A 7A 8A ***** Summary: Writing Names and Formulas 1. The name of an element is the name of its atoms. 2. In covalent bonds, electrons are shared. Two nonmetal atoms usually bond with a covalent bond. 3. An ionic bond exists between positive and negative ions. If a metal is bonded to a nonmetal, the bond is generally ionic. The metal is the positive ion. 4. Most compounds with all nonmetal atoms are covalent. Most compounds that have both metal atoms and nonmetal atoms are ionic. 5. If a compound has only covalent bonds, it is covalent. If a compound has one or more ionic bonds, it is ionic. 6. Naming binary covalent compounds: a. Names have two words. b. Compounds that include hydrogen have many exceptions. Compounds with O end in (prefix)oxide. (This rule has precedence.) © 2011 www.ChemReview.Net v.n4 Page OS 163 Module 7 – Writing Names and Formulas c. The first word contains the name of the atom in the column farther to the left in the periodic table. For two atoms in the same column, the lower one is named first. d. The second word contains the root of the second atom name plus a suffix -ide. e. The number of atoms is shown by a prefix. • Mono- = 1 atom. (For the first word of the name, mono is left off and is assumed if no prefix is given.) • Di- = 2 atoms, Tri- = 3, Tetra- = 4, Penta- = 5, Hexa- = 6, Hepta- = 7, Octa- = 8. 7. Positive ions are cations (pronounced CAT-eye-uns). Negative ions are anions (pronounced ANN-eye-uns). 8. Metals can lose electrons to form positive ions. Column one atoms form 1+ ions column two atoms form 2+ ions. 9. The name of a metal ion that forms only one ion is the name of the atom. 10. Metals to the right of column 2 often form two different cations. The name of these ions is • the atom name followed by (I, II, III, or IV) stating the positive charge, • or a common name consisting of the Latin root plus –ous for the lower-charged ion or–ic for the higher-charged ion. 11. A polyatomic ion is composed of more than one atom. 12. The name of monatomic anions is the root followed by -ide. 13. For oxyanions of a given atom, the per–root–ate, root-ate, root-ite, and hypo-root-ite ions each have the same charge, but one fewer oxygens, respectively. 14. Ionic compounds have positive and negative ions in ratios that guarantee electrical neutrality. 15. To determine the names and formulas for ionic compounds, • write the separated-ions formula first, and • be certain that all names and formulas are electrically neutral. 16. To balance separated-ion formulas, add coefficients that balance charge. Coefficients are numbers written in front of symbols that show the ratio of the ions. In balancing, you may not change the symbol or the stated charge of an ion. (Coefficient times charge of cation) must balance (coefficient times charge of anion). The overall charge for ionic compounds must equal zero. 17. To write solid formulas for ionic compounds from their names, follow these steps. • Write the separated ions with the lowest whole-number coefficient ratios. • Write the two ion symbols, positive ion first, without charges, a + sign, or coefficients. • Put parentheses ( ) around polyatomic ions IF you need more than one. • Make the separated formula coefficients into solid formula subscripts. Omit subscripts of 1. © 2011 www.ChemReview.Net v.n4 Page OS 164 Module 7 – Writing Names and Formulas 18. To write separated ions from solid formulas, • decide the negative ion’s charge and coefficients first. • Add the positive ion’s charge based on what balances atoms and charge. Assume that metal atoms are monatomic (except Hg 2+). • 2 19. To name an ionic compound: name the ions, positive first. 20. To name acid solutions, memorize these: • H2SO4 = sulfuric acid, H2SO3 = sulfurous acid, H3PO4 = phosphoric acid. • HCl = hydrochloric acid, HF = hydrofluoric acid, HBr = hydrobromic acid, and HI = hydroiodic acid. 21. If an acid contains an H+ ion and an oxoanion, to name the acid: a. Write the name of the oxoanion, then cross off the suffix to form the root name. b. If the ion suffix was –ate , replace the suffix with –ic followed by the word acid. c. If the ion suffix was –ite , replace the suffix with –ous acid. ***** ANSWERS – Module 5-7 Review Quiz Some partial solutions are provided below. Your work on calculations should include WANTED, DATA, and SOLVE. 1. 1.60 x 10─17 coulombs ? coulombs = 100. electrons • 1 mole of electrons • 96,500 coulombs = 6.02 x 1023 electrons 1 mole of electrons (0.3048 m)2 1 foot 2. 1,010 m2 ? m2 = 0.250 acres • 43,560 ft2 • 1 acre 3. 39 mL Vcylinder = π r2 h = π (2.5 cm)2(2.0 cm) = 39 cm3 = 39 mL 4. 235U and U2+ 6. 107.1 amu 7. b. H, I, He, P, C 8c. K+ and CrO42─ HI 9e. HNO2 9d. 5. 47 protons, 60 neutrons, and 46 electrons ave. mass = (104.0 g/mol x 0.220) + (108.0 g/mol x 0.780) = 8a. Ag+ and SO42─ 9a. Na2Cr2O7 9f. HBrO3 10b. Potassium hypochlorite 10d. Iron(III) sulfite = 8b. Na+ and OH─ 9b. (NH4)3PO4 9c. Al(IO3)3 10a. Dibromine heptoxide (or heptaoxide) 10c. Sodium hydrogen carbonate (or sodium bicarbonate) 10e. Acetic acid 10f. Hypobromous acid 11. See a periodic table. ##### © 2011 www.ChemReview.Net v.n4 Page OS 165 Module 7 – Writing Names and Formulas * **** NOTE on the Table of Atoms The atomic masses in this Table of Atoms use fewer significant figures than most similar tables in college textbooks. By “keeping the numbers simple,” it is hoped that you will use “mental arithmetic” to do easy numeric cancellations and simplifications before you use a calculator for arithmetic. Many calculations in these lessons have been set up so that you should not need a calculator at all to solve, if you look for easy cancellations first. After any use of a calculator, use mental arithmetic and simple cancellations to estimate the answer, in order to catch errors in calculator use. ##### The ATOMS – The third column shows the atomic number: The protons in the nucleus of the atom. The fourth column is the molar mass, in grams/mole. For radioactive atoms, ( ) is the molar mass of most stable isotope. Actinium Aluminum Americium Antimony Argon Arsenic Astatine Barium Berkelium Beryllium Bismuth Boron Bromine Cadmium Calcium Californium Carbon Cerium Cesium Chlorine Chromium Cobalt Copper Curium Dysprosium Erbium Europium Fermium Fluorine Francium Gadolinium Gallium Germanium Gold Hafnium Helium Holmium Hydrogen Indium Iodine Iridium Iron Krypton Lanthanum Lawrencium Lead Lithium Ac Al Am Sb Ar As At Ba Bk Be Bi B Br Cd Ca Cf C Ce Cs Cl Cr Co Cu Cm Dy Er Eu Fm F Fr Gd Ga Ge Au Hf He Ho H In I Ir Fe Kr La Lr Pb Li 89 13 95 51 18 33 84 56 97 4 83 5 35 48 20 98 6 58 55 17 24 27 29 96 66 68 63 100 9 87 64 31 32 79 72 2 67 1 49 53 77 26 36 57 103 82 3 (227) 27.0 (243) 121.8 40.0 74.9 (210) 137.3 (247) 9.01 209.0 10.8 79.9 112.4 40.1 (249) 12.0 140.1 132.9 35.5 52.0 58.9 63.5 (247) 162.5 167.3 152.0 (253) 19.0 (223) 157.3 69.7 72.6 197.0 178.5 4.00 164.9 1.008 114.8 126.9 192.2 55.8 83.8 138.9 (257) 207.2 6.94 Lutetium Magnesium Manganese Mendelevium Mercury Molybdenum Neodymium Neon Neptunium Nickel Niobium Nitrogen Nobelium Osmium Oxygen Palladium Phosphorus Platinum Plutonium Polonium Potassium Praseodymium Promethium Protactinium Radium Radon Rhenium Rhodium Rubidium Ruthenium Samarium Scandium Selenium Silicon Silver Sodium Strontium Sulfur Tantalum Technetium Tellurium Terbium Thallium Thorium Thulium Tin Titanium Tungsten Uranium Vanadium Xenon Ytterbium Yttrium Zinc Zirconium Lu Mg Mn Md Hg Mo Nd Ne Np Ni Nb N No Os O Pd P Pt Pu Po K Pr Pm Pa Ra Rn Re Rh Rb Ru Sm Sc Se Si Ag Na Sr S Ta Tc Te Tb Tl Th Tm Sn Ti W U V Xe Yb Y Zn Zr 71 12 25 101 80 42 60 10 93 28 41 7 102 76 8 46 15 78 94 84 19 59 61 91 88 86 75 45 37 44 62 21 34 14 47 11 38 16 73 43 52 65 81 90 69 50 22 74 92 23 54 70 39 30 40 175.0 24.3 54.9 (256) 200.6 95.9 144.2 20.2 (237) 58.7 92.9 14.0 (253) 190.2 16.0 106.4 31.0 195.1 (242) (209) 39.1 140.9 (145) (231) (226) (222) 186.2 102.9 85.5 101.1 150.4 45.0 79.0 28.1 107.9 23.0 87.6 32.1 180.9 (98) 127.6 158.9 204.4 232.0 168.9 118.7 47.9 183.8 238.0 50.9 131.3 173.0 88.9 65.4 91.2 ...
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