Ions7C - Module 7 – Writing Names and Formulas Naming...

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Unformatted text preview: Module 7 – Writing Names and Formulas Naming Ionic Compounds: Self-Study Assignment You will have a QUIZ on the attached pages on _____________________ . Your assignment is: READ the pages attached. WORK the examples in the lesson. Complete the pages as homework. To work the examples, • use a sheet of paper to cover below the * * * * * line, • try the problem on your paper, • then check your answer below the * * * * * line. Start early. This assignment will require 2-4 hours of work outside of class. Lesson 7B: Naming Ions Prerequisites: Complete Module 6 and Lesson 7A before starting this lesson. 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 In ionic compounds, the constituent particles are ions, particles with an electrical charge. In most first-year chemistry courses you will be asked to memorize the names and symbols for more than 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. © 2009 www.ChemReview.Net v.m8 Page 128 Module 7 – Writing Names and Formulas Categories of Ions 1. All ions are either positive or negative. • Positive ions are termed cations (pronounced KAT-eye-ons). The charges on positive ions can be 1+, 2+, 3+, or 4+. • Negative ions are termed anions (pronounced ANN-eye-ons). The charges on negative ions can be 1─, 2─, or 3─. 2. All ions are either monatomic or polyatomic. • A monatomic ion is composed of a single atom. Examples of monatomic ions are 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 of polyatomic ions are OH─, Hg22+, NH4+, and SO42─. Ions of Hydrogen Hydrogen has unique characteristics. It is classified as a nonmetal, and in most of its compounds hydrogen bonds covalently. In compounds classified as acids, hydrogen can form H+ ions (protons). When bonded to metal atoms, hydrogen behaves as a hydride ion (H─). The Structure and Charge of Metal Ions More than 70% of the elements in the periodic table are metal atoms. • Geologically, in the earth’s crust, most metals are found as metal ions. When metal ions are found in rocks from which the ions can be extracted and converted to metals, the rocks have economic value and are termed ores. Famous 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 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. The charge can be 1+, 2+, 3+, or 4+. • 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 positive ion. Some frequently encountered metals form two stable ions. In many cases, the charge (or possible charges) on a 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 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. © 2009 www.ChemReview.Net v.m8 Page 129 Module 7 – Writing Names and Formulas Metal Ions With One Charge Metals in the first two columns of the periodic table form only one ion. The charge on that ion is easy to predict. • All metals in column one (the alkali metals) form ions that are single atoms with a 1+ charge: Li+, Na+, K+, Rb+, Cs+, and Fr+. • All metals in column two form ions that are single atoms 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 in later parts of your course. In order to solve problems initially, most courses require that the possible charges on certain metals to the right of column 2 in the periodic table 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 Ni2+, Ag+, Zn2+, Cd2+, 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 element name. Examples: Na+ is a sodium ion. Al3+ is an aluminum ion. This rule applies to • metal ions in columns one and two, plus • the additional five metal ions listed above, plus • additional ions that may be studied in later parts of first-year chemistry. 2. For metals that form two different positive ions, the systematic name (or modern name) of the ion is the element 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) 3. For metals that form two different positive ions and were “known to the ancients” also have common names for their ions. In common names, the lower charged ion uses the Latin root of the element name plus the suffix –ous. The higher-charged ion uses the Latin root plus the suffix –ic. © 2009 www.ChemReview.Net v.m8 Page 130 Module 7 – Writing Names and Formulas For metal ions, the systematic (roman numeral) names are preferred, but the common names are often encountered. Most courses require that the names and symbols for the following ions, and perhaps others, be memorized. Ion Symbol Systematic Ion Name Common Ion Name Cu+ copper(I) cuprous Cu2+ copper(II) cupric Fe 2 + iron(II) ferrous Fe 3 + iron(III) ferric Sn2+ tin(II) stannous Sn4+ tin(IV) stannic Hg22+ mercury(I) mercurous Hg2+ mercury(II) mercuric Lead also forms two ions. Pb2+ is named lead(II), and Pb4+ is named lead(IV). The common names plumbous and plumbic are rarely used. 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 respects as two loosely bonded +1 ions. When to Include Roman Numerals In Systematic Names When naming metal ions, the rule is: Do not use roman numerals in systematic names for metal ions that can form only one stable ion: ions for atoms in the first two columns, plus Ni2+, Ag+, Zn2+, Cd2+, and Al3+. However, for ions of the transition metals, adding the roman numeral, such as using nickel(II) for Ni2+, may be acceptable in your course. Summary: Metal Ion Rules • All metal ions are positive. Except for Hg22+, all metal atoms are monatomic. • In column one, all elements tend to form 1+ ions. • In column two, all elements tend to form 2+ ions. • For the metals to the right of column 2, five metals form only one ion: Ni2+, Ag+, Zn2+, Cd2+, and Al3+. Assume that the others form more than one ion. • If a metal forms only one ion, the ion name is the element name. • If a metal forms more than one ion, the systematic ion name is the element name followed by a roman numeral in parentheses showing the positive charge of the ion. © 2009 www.ChemReview.Net v.m8 Page 131 Module 7 – Writing Names and Formulas 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 positive ion anion 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 ion name needed? In systematic names, if the metal forms more than one kind of positive ion In systematic names for metal ions, which do not need (roman numerals) to show their charge? Columns 1 and 2, plus Ni2+, Ag+, Zn2+, Cd2+, and Al3+ Practice A: Use a periodic table. Memorize the rules, ion symbols, and names in the section above before doing the problems. On multi-part questions, save a few parts for your next study session. 1. Add a charge to show the symbol for the stable ion that these elements 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 + © 2009 www.ChemReview.Net v.m8 Page 132 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 (the ─1 ions of halogens): 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 element name followed by -ide. For monatomic ions, the position of the element in the periodic table predicts the charge. Group 1A Family Name Alkali Metals Charge on Monatomic ion 1+ 2A 3A 4A 2+ 7A 8A O Family Halogens Noble Gases 3─ 3+ (or 1+) 6A N Family Transition Metals 5A 2─ 1─ None Polyatomic Ions A polyatomic ion is a particle that both 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 NH + (ammonium), H O+ (hydronium), and Hg 2+ (mercury(I) or mercurous) ions. 4 3 © 2009 www.ChemReview.Net v.m8 2 Page 133 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 = NO ─ , nitrite ion = NO ─ 3 2 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. To simplify naming these ions, memorize the formula for one ion in a series, then write out the rest by logic as needed. With practice, this naming process will become automatic. ***** Memorizing 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. Even if it is not required, doing so will speed your work and improve your understanding of chemistry. The following set of flashcards is information that you will rely on heavily for the remainder of the year. 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 that have more than one possible charge, but learning those names and charges will help you to recall what charges are likely to be found on those metal ions. © 2009 www.ChemReview.Net v.m8 Page 134 Module 7 – Writing Names and Formulas Make and learn these flashcards on 3” by 5” index cards CH3COO─ acetate Cu+ cuprous CN─ OH─ cyanide cupric hydroxide Cu2+ Fe2+ ferrous NO3─ nitrate Fe3+ ferric MnO4─ permanganate Sn2+ stannous C O3 2 ─ carbonate Sn4+ stannic HCO3─ hydrogen carbonate Hg22+ mercurous or mercury (I) CrO42─ chromate Hg2+ mercuric Cr2O72─ dichromate O2 ─ oxide P O4 3 ─ phosphate S2 ─ sulfide SO42─ sulfate N3─ nitride SO32─ sulfite P3─ phosphide Na+ sodium ion ClO4─ perchlorate K+ potassium ion ClO3─ chlorate Al3+ aluminum ion ClO2─ chlorite F─ Cl─ fluoride ClO─ H+ hypochlorite chloride hydrogen ion iodide H─ Mg2+ magnesium ion Ca 2 + calcium ion NH4+ ammonium Ba 2 + barium ion H3O+ hydronium Br─ I─ bromide hydride ***** © 2009 www.ChemReview.Net v.m8 Page 135 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. Work in your notebook. Repeat these again after a few days of flashcard practice. 1. In this chart of ions, from memory, add charges, names, and ion formulas. Symbol C O3 Ion name 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________________ __________________ ANSWERS Practice A 1. a. Ba2+ 2. a. Cd2+ b. Al3+ b. L i+ c. H─ © 2009 www.ChemReview.Net v.m8 c. Rb+ d. Ca2+ d. Na+ e. Zn2+ f. Ag+ 3. Only the hydride ion (H─). 4. Hg22+ Page 136 Module 7 – Writing Names and Formulas 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 Practice B 1,2. Symbol 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─ 3. 4. Ion name fluorine B a 2+ barium NO2─ Ion name Ion Symbol Perbromate BrO4─ Bromate BrO3─ Bromite BrO2─ Hypobromite BrO─ © 2009 www.ChemReview.Net v.m8 Page 137 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. Answers are at the end of the lesson. 1. Name Pb3(PO4)2 2. Write formulas for a. tin(IV) chlorate b. radium nitrate. ***** Ionic Compounds: Fundamentals Positive and negative ions combine to form ionic compounds. Ionic compounds must have both positive and negative ions. There is only one ratio possible for the ions in a compound. The ions must combine in a ratio that results in electrical neutrality. This means that the charges in any ionic substance must balance. The overall charge of any stable combination of ions must be zero. Names and Formulas The composition of an ionic compound can be expressed in three ways. • In a name; • As a solid formula; • Example: ammonium phosphate Example: (NH4)3PO4 As balanced, separated ions. Example: 3 NH4+ + 1 PO43─ As a part of solving many upcoming chemistry problems, given one of these expressions, you will need to be able 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. The key to writing a correct name and solid formula is to first write the separated-ions formula that shows the number and the formulas of the ions in the combination, including their charges. For ionic compounds, the fundamental rules for writing names and formulas are: • Always write the separated-ions formula first, and • Add coefficients that balance the charges. Balancing Separated Ions In all combinations 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 charge is zero. In problems, you will often be asked to determine the ratios that balance the charges. The way to find those ratios is to write a balanced separated-ions formula for the compound. Let’s learn the method with an example. Q. Find the ratio that balances the charges when S2─ and Na+ combine. Try this problem using these steps, then check your answer below. © 2009 www.ChemReview.Net v.m8 Page 138 Module 7 – Writing Names and Formulas Step 1: Write the symbols for the two ions in the compound, with their charges, separated by a + sign. It is preferred to put the positive ion first. Step 2: Coefficients are numbers written in front of ion or particle symbols. In all ion combinations, (Coefficient times charge of cation) must equal (coefficient times charge of anion). Write the whole-number coefficients in front of the ion formulas that make the positive and negative charges balance. In balancing, you cannot change the symbol or the stated charge of an ion. The only change allowed is to add coefficients in front of the particle symbols. Step 3: Reduce the coefficients to the lowest whole-number ratios. ***** Step 1: Answer Step 2: Na+ + S2─ 2 Na+ + 1 S2─ This is the separated-ions formula. The coefficients that balance the charges show the ratios in which the ions must exist in the compound. Step 3: 2 and 1 are the lowest whole-number ratios. 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 so that the total positive and negative charges balance. Only one set of coefficient ratios will balance the charges. The coefficients identify the ratios in which the ions are 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: An easy way to find the coefficients is to make the coefficient of each ion equal to the number of charges 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 must often adjust the coefficients so that the final coefficients are the lowest whole-number ratios. Try this problem. Q. Add proper coefficients: ____ Ba2+ + ____ SO42─ ***** © 2009 www.ChemReview.Net v.m8 Page 139 Module 7 – Writing Names and Formulas Answer If balancing produces a ratio of 2 Ba2+ + 2 SO42─ , write the final coefficients as 1 Ba2+ + 1 SO42─ . When balancing ions, make the coefficients the lowest whole-number ratios. Practice A: Add lowest-whole-number coefficients to make these separated ions balanced for charge. After every two, check your answers at the end of the lesson. 1. ____ Na+ + ____ Cl─ 5. NH4+ + CH3COO─ 2. ____ Ca2+ + ____ Br─ 6. In3+ + CO32─ 3. Mg2+ + SO42─ 7. Al3+ + 4. Cl─ Al3+ 8. HPO42─ + + PO43─ In3+ Writing the Separated Ions from Names To write the separated ions from the name of an ionic compound, use these steps. Step 1: Write the symbols for the two named ions, with their charges, separated by a + sign. The first word in the name is always the positive ion. Step 2: Add lowest-whole-number coefficients to balance the charges. Try those the steps on this problem: Q. Write a balanced separated-ions formula for aluminum carbonate. ***** 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 charge high, the subscript low, and the coefficient at the same level as the symbol. Practice B If you have not done so today, run your ion flashcards one more time. Then write balanced separated-ions formula for the ionic compounds below. You may use a periodic table, but otherwise write the ion formulas from memory. Check answers as you go. 1. Sodium hydroxide 2. Aluminum chloride © 2009 www.ChemReview.Net v.m8 Page 140 Module 7 – Writing Names and Formulas 3. Rubidium sulfite 4. Ferric nitrate 5. Lead(II) phosphate 6. Calcium chlorate 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. 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 no charges or coefficients. 3. For the ion symbols written after the arrow, put parentheses () around a polyatomic ion if its coefficient in the separated-ions formula is more than 1. 4. Add subscripts after each symbol on the right. The subscript will 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. Apply those four 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 a 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. ***** © 2009 www.ChemReview.Net v.m8 Page 141 Module 7 – Writing Names and Formulas Try another using the same steps. Q. Write the solid formula for magnesium phosphate. ***** Answer 3 Mg2+ + 2 PO43─ 1: Write the balanced separated ions. Magnesium phosphate 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 >1, so add ( ) . Mg (PO4) 4: The separated coefficient of the Mg ion becomes its solid subscript. Mg3(PO4) The phosphate ion’s separated coefficient becomes its solid subscript. Mg3(PO4)2 Mg3(PO4)2 is the solid formula for magnesium phosphate. Recite the 3-P’s rule for ionic-solid formulas until it is memorized. 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. Ca2+ e. OH─ 2. When do you need parentheses? Write the rule from memory. 3. Write solid formulas for these ion combinations. a. 2 K+ + 1 CrO42─ b. 2 NH4+ + 1 S2─ c. 1 SO32─ + 1 Sr2+ 4. Balance these separated ions for charge, then write solid formulas. a. Cs+ + b. Cr2O72─ + c. Sn4+ + N3─ Ca2+ SO42─ © 2009 www.ChemReview.Net v.m8 Page 142 Module 7 – Writing Names and Formulas 5. 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 6. Write the solid formula. a. Stannous fluoride b. Calcium hydroxide c. Radium acetate Writing Separated Ions From Solid Formulas When placed in water, all ionic solids dissolve to some extent. The dissolved ions separate and move about 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 solid, and (aq) is an abbreviation for aqueous, which means “dissolved in water.” An equation for ion separation must balance atoms, balance charge, and result in the 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. 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. ***** © 2009 www.ChemReview.Net v.m8 Page 143 Module 7 – Writing Names and Formulas 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 will identify the positive ion’s charge, so do 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 Step 2: Cu2 and 1 CO32─ . 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. ***** © 2009 www.ChemReview.Net v.m8 Page 144 Module 7 – Writing Names and Formulas 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 2 NH4 + 1 S 2 NH4+ + 1 S2─ • Assign the charges that these ions prefer. (NH4)2S • 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 essential in the complex problems 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 you 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. Mn(OH)2 © 2009 www.ChemReview.Net v.m8 Page 145 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 in the formula. Step 3. Write 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 named first. Try this problem. Q. What is the name of K2CO3? ***** Answer 2 K+ + 1 CO32─ ; the name is potassium carbonate. K2CO3 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. 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 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 ***** © 2009 www.ChemReview.Net v.m8 Page 146 Module 7 – Writing Names and Formulas Practice F: Combining Ions Worksheet Fill in the blanks. Do half today and the rest during your next study session. Check answers at the end of the lesson. 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 Cuprous chloride Tin(II) fluoride __ A13+ + __ Cr2O72─ K2CrO4 CaCO3 Aluminum phosphate © 2009 www.ChemReview.Net v.m8 Page 147 Module 7 – Writing Names and Formulas ANSWERS Pretest: 1. Lead(II) phosphate 2a. Sn(ClO3)4 2b. Ra(NO3)2 Practice A 4. 3 Cl─ + 1 Al3+ 5. 1 NH4+ + 1 CH3COO─ 6. 2 In3+ + 3 CO32─ 1. 1 Na+ + 1 Cl─ 2. 1 Ca2+ + 2 Br─ 3. 1 Mg2+ + 1 SO42─ 7. 1 Al3+ + 1 PO43─ 8. 3 HPO42─ + 2 In3+ Practice B 1. Sodium hydroxide 1 Na+ + 1 OH─ 2. Aluminum chloride 1 Fe3+ + 3 NO3─ 5. Lead(II) phosphate 3 Pb2+ + 2 PO43─ 1 Al3+ + 3 Cl─ 4. Ferric nitrate 2 Rb+ + 1 SO32─ 3. Rubidium sulfite 6. Calcium Chlorate 1 Ca2+ + 2 ClO3─ 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. Cs N 4a. 3 Cs+ + 1 N3─ 3a. 2 K+ + 1 CrO 2─ K CrO 4 2 4 (NH4)2S 3b. 2 NH4+ + 1 S2─ 3c. 1 SO32─ + 1 Sr2+ SrSO3 3 4b. 1 Cr2O72─ + 1 Ca2+ CaCr2O7 4c. 1 Sn4+ + 2 SO42─ Sn(SO4)2 5a. 2 NH4+ + 1 SO32─ 5c. 1 Ca2+ + 2 OCl─ (NH4)2SO3 5b. 1 K+ + 1 MnO4─ 5d. 1 Na+ + 1 HCO3─ KMnO4 Ca(ClO)2 NaHCO3 6. Write balanced, separated ions first to help with the solid formula. a. Stannous fluoride 1 Sn2+ + 2 F─ b. Calcium hydroxide 1 Ca2+ + 2 OH─ SnF2 1 Ra2+ + 2 CH3COO─ c. Radium acetate Ca(OH)2 Ra(CH3COO)2 Practice D and E 1. a. PbCO3 b. Hg2SO4 1 Pb2+ + 1 CO32─ (Lead(II) carbonate) 1 Hg 2+ + 1 SO 2─ (Mercurous sulfate or Mercury(I) sulfate) 2 4 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. Mn(OH)2 1 Mn2+ + 2 OH─ (Manganese hydroxide) © 2009 www.ChemReview.Net v.m8 Page 148 Module 7 – Writing Names and Formulas E2. C3a. Potassium chromate C4a. Cesium nitride C3b. Ammonium sulfide C3c. Strontium sulfite C4b. Calcium dichromate C4c. Tin(IV) sulfate or stannic 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. Tetraphosphorous trisulfide Practice F Ionic Compound NAME SEPARATED Ions SOLID Formula Sodium chloride 1 Na+ + 1 Cl─ NaCl Aluminum sulfite 2 A13+ + 3 SO32─ A12(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 Cuprous chloride 1 Cu+ + 1 Cl─ CuCl Tin(II) fluoride 1 Sn 2 + + 2 F─ SnF2 Aluminum dichromate 2 A13+ + 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 © 2009 www.ChemReview.Net v.m8 Page 149 ...
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This note was uploaded on 11/16/2011 for the course CHM 1025 taught by Professor J during the Summer '09 term at Santa Fe College.

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