ChemMod7Naming - Module 7 – Writing Names and Formulas...

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Unformatted text preview: 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 easily distinguishes 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 120 Module 7 – Writing Names and Formulas Compounds In compounds, there is more than one kind of atom, but all the neutral molecules or formula units have the same atoms and structure. Most compounds can be classified as either ionic or covalent. Covalent compounds are molecules. They contain atoms bonded together by electrons shared between atoms. The attractive forces (bonds) within molecules are strong compared to the attractions between molecules. Compounds that are gases or liquids at room temperature are nearly always covalent compounds. At room temperature, compounds that are solids may be ionic or covalent, but ionic compounds are always solids. Ionic compounds are composed of an array of ions bonded strongly by electrostatic attraction. Types of 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. (H) C 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. 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. 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 * * * * * © 2011 www.ChemReview.Net v.n4 Page 121 Module 7 – Writing Names and Formulas Answers 1. C─H Both are non-metals; predict a covalent bond 2. Na─C A metal and a non-metal atom; predict ionic bond 3. N─Cl Two non-metals; predict covalent bond 4. K─Cl A metal and non-metal; predict 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. 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. © 2011 www.ChemReview.Net v.n4 Page 122 Module 7 – Writing Names and Formulas 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 Naming Binary Covalent Compounds Binary covalent compounds contain two different nonmetals. The naming of binary compounds uses the atom name or the root of the atom name. 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. 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 © 2011 www.ChemReview.Net v.n4 Page 123 Module 7 – Writing Names and Formulas 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? * * * * * (the * * * mean cover the answer below, write your answer, then check it.) 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? * * * * * 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 = ? © 2011 www.ChemReview.Net v.n4 Page 124 Module 7 – Writing Names and Formulas 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 c. SO2 d. NO 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 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.) 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 125 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 bonds covalently in many compounds. However, in compounds classified as acids, one or more hydrogens form H+ ions when the compound is dissolved in water. When bonded to metal atoms, hydrogen behaves as the hydride ion H─. The Structure and Charge of Metal Ions More than 70% of the atoms in the periodic table are classified as metal atoms. • 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 126 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 127 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 Fe2+ Fe3+ 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 128 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 129 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) Fe2+ 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 © 2011 www.ChemReview.Net v.n4 3A 3+ (or 1+) 5A 6A 7A 8A N Family Transition Metals 4A O Family Halogens Noble Gases 3─ 2─ 1─ None Page 130 Module 7 – Writing Names and Formulas 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. 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. © 2011 www.ChemReview.Net v.n4 Page 131 Module 7 – Writing Names and Formulas 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. 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 Cu+ cuprous/copper(I) CN─ OH─ cyanide cupric/copper(II) hydroxide Cu2+ Fe2+ NO3─ nitrate Fe3+ ferric/iron(III) MnO4─ permanganate Sn2+ stannous/tin(II) CO32─ carbonate Sn4+ stannic/tin(IV) HCO3─ hydrogen carbonate Hg22+ CrO42─ chromate Hg2+ mercurous or mercury(I) mercuric or mercury(II) Cr2O72─ dichromate O2 ─ oxide PO43─ phosphate S2 ─ sulfide SO42─ sulfate N3─ nitride SO32─ sulfite P3─ phosphide © 2011 www.ChemReview.Net v.n4 ferrous/iron(II) Page 132 Module 7 – Writing Names and Formulas 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 Ca2+ calcium ion NH4+ ammonium Ba2+ barium ion H3O+ hydronium Br─ I─ bromide hydride 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 CO3 acetate radium MnO4 CN silver CrO4 hydroxide K Al dichromate ClO4 PO4 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? © 2011 www.ChemReview.Net v.n4 Page 133 Module 7 – Writing Names and Formulas 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+ b. Al3+ c. Rb+ c. H─ d. Na+ d. Ca2+ e. Zn2+ f. Ag+ 3. Only the hydride ion (H─). 2. a. Cd2+ b. Li+ 4. Hg22+ 5. Ion Symbol Systematic Ion Name Common Name Sn4+ tin(IV) stannic Cu2+ copper(II) cupric Fe3+ iron(III) ferric Cu+ copper(I) cuprous Fe2+ iron(II) ferrous Practice B Symbol Ion name CO32─ carbonate CH3COO─ acetate Ra2+ radium CN─ cyanide MnO4─ permanganate Ag+ silver CrO42─ chromate OH─ hydroxide K+ potassium Al3+ aluminum Cr2O72─ dichromate ClO4─ perchlorate PO43─ phosphate NO3─ nitrate SO42─ sulfate Na+ sodium S2─ sulfide F─ 1,2. fluoride Ba2+ barium © 2011 www.ChemReview.Net v.n4 Page 134 Module 7 – Writing Names and Formulas 3. NO2─ 4. Ion name Ion Symbol Perbromate BrO4─ Bromate BrO3─ Bromite BrO2─ Hypobromite BrO─ * * * * * 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 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; • And as balanced, separated ions. Example: ammonium phosphate Example: (NH4)3PO4 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. 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. © 2011 www.ChemReview.Net v.n4 Page 135 Module 7 – Writing Names and Formulas 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 ion combinations, (Coefficient times charge of cation) must balance (coefficient times charge of anion). In balancing, you cannot change the symbol or the charge of an ion. In 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. * * * * * Step 1. Answer 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. © 2011 www.ChemReview.Net v.n4 Page 136 Module 7 – Writing Names and Formulas 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 produces electrical neutrality. 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+ 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 the 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 137 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 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 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. © 2011 www.ChemReview.Net v.n4 Page 138 Module 7 – Writing Names and Formulas 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─ K S 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. * * * * * 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─ S2─ © 2011 www.ChemReview.Net v.n4 Page 139 Module 7 – Writing Names and Formulas c. SO32─ + d. Sn4+ + 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 5. Write the solid formula. a. Tin(II) 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 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 © 2011 www.ChemReview.Net v.n4 Page 140 Module 7 – Writing Names and Formulas 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 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. © 2011 www.ChemReview.Net v.n4 Page 141 Module 7 – Writing Names and Formulas 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 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 most helpful in solving the complex 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 © 2011 www.ChemReview.Net v.n4 Page 142 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 . * * * * * 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 * * * * * © 2011 www.ChemReview.Net v.n4 Page 143 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 144 Module 7 – Writing Names and Formulas ANSWERS Pretest: 1. Lead(II) phosphate 2a. Sn(ClO3)4 2b. Ra(NO3)2 Practice A 3. 3 Cl─ + 1 Al3+ 4. 1 NH4+ + 1 CH3COO─ 1. 1 Na+ + 1 Cl─ 2. 1 Mg2+ + 1 SO 2─ 4 5. 1 Al3+ + 1 PO43─ 6. 3 HPO42─ + 2 In3+ Practice B 1 Na+ + 1 OH─ 3. Lead(II) phosphate 2 Rb+ + 1 SO32─ 4. Calcium perchlorate 1. Sodium hydroxide 2. Rubidium sulfite 3 Pb2+ + 2 PO43─ 1 Ca2+ + 2 ClO4─ 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 3d. 1 Sn4+ + 2 SO42─ (NH4)2S 4a. 2 NH4+ + 1 SO32─ 4c. 1 Ca2+ + 2 OCl─ (NH4)2SO3 4b. 1 K+ + 1 MnO4─ 4d. 1 Na+ + 1 HCO3─ KMnO4 3 Sn(SO4)2 Ca(ClO)2 NaHCO3 5. Write balanced, separated ions first. 1 Sn2+ + 2 F─ a. Tin(II) fluoride b. Calcium hydroxide c. Radium acetate SnF2 1 Ca2+ + 2 OH─ Ca(OH)2 1 Ra2+ + 2 CH3COO─ Ra(CH3COO)2 Practice D and E 1. a. PbCO3 b. Hg2SO4 1 Pb2+ + 1 CO32─ 1 Hg22+ + 1 SO42─ Part E: Lead(II) carbonate 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 © 2011 www.ChemReview.Net v.n4 Page 145 Module 7 – Writing Names and Formulas 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 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 Sn2+ + 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 146 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 147 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 148 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. 1c. Nitric acid by rule 3 from nitrate ion. 2a. 2c. Bromous acid must include bromite ion which is BrO2─, so the acid must be HBrO2(aq) . Sulfurous acid is memorized as H2SO3(aq) . Chromic acid must come from chromate ion which is CrO 2─, so the acid must be H CrO 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─ 2b. 1b. Hypoiodous acid by rule 3 from hypoiodite ion. 1d. Phosphoric acid by rule 1. 4 2 4(aq) . H3AsO4(aq) . Arsenate ion is the anion in arsenic acid. * * * * * © 2011 www.ChemReview.Net v.n4 Page 149 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 150 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 151 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 152 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 8b. Na+ and OH─ 9b. (NH4)3PO4 9c. Al(IO3)3 10a. Dibromine heptoxide (or heptaoxide) 9f. HBrO3 10b. Potassium hypochlorite 10d. Iron(III) sulfite = 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 153 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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This note was uploaded on 03/12/2012 for the course CHEMISTRY 131 taught by Professor Lacey during the Fall '11 term at SUNY Stony Brook.

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