33 Ionic Compounds Introduction to Bonding Bonding is the joining of two atoms in a stable arrangement. There are two different kinds of bonding: Elements will gain, lose, or share electrons to attain the electron configuration of the noble gas closest to them in the periodic table. Ionic bonds result from the transfer of electrons from one element to another. Covalent bonds result from the sharing of electrons between two atoms.
4 Sample Problem 3.1 Solution (a) Na = metal; I = nonmetal NaI = ionic (b) H and O = nonmetal H 2 O 2 = covalent Question Predict whether the bonds in the following compounds are ionic or covalent: (a) NaI (sodium iodide) (b) H 2 O 2 (hydrogen peroxide)
55 Ionic Compounds Ionic Bonding Ionic bonds form between: a metal on the left side of the periodic table a nonmetal on the right side of the periodic table Na+Cl 2 NaCl sodium metal chlorine gas sodium chloride crystals
66 Ionic Compounds Covalent Bonding Covalent bonds are formed when two nonmetals combine, or when a metalloid bonds to a nonmetal. A molecule is a discrete group of atoms that share electrons.
77 Ions Cations and Anions Ions are charged species in which the number of protons and electrons in an atom is unequal. Ionic compounds consist of oppositely charged ions that have a strong electrostatic attraction for each other. There are two types of ions—cations and anions.
88 Ions Cations and Anions Cations are positively charged ions. A cation has fewer electrons (e − ) than protons.
99 Ions Cations and Anions By losing one, two, or three e −, an atom forms a cation with a completely filled outer shell of e −.
10 Ions Cations and Anions Anions are negatively charged ions. An anion has more e − than protons.
11 Sample Problem 3.3 Question How many electrons are present in (a) Ca 2+ (b) O 2- Solution Ca atomic number = 20 Ca 2+ has 18 electrons O atomic number = 8 O 2- has 10 electrons
12 Ions The Octet Rule The octet rule: a main group element is especially stable when it possesses an octet of e − in its outer shell. By gaining one, two, or three electrons, an atom forms an anion with a completely filled outer shell of e −. octet = 8 valence e −
13 Ions Relating Group Number to Ionic Charge for Main Group Elements Elements in the same group form ions of similar charge. Metals form cations. For metals in groups 1A, 2A, and 3A, the group number = the charge on the cation. Nonmetals form anions. For nonmetals in Groups 6A and 7A, the anion charge = 8 – the group number.
14 Ions Relating Group Number to Ionic Charge for Groups 1A–3A group 1A: group 2A: group 3A: M 1 valence e − M + + e − M 2 valence e − M e − M 3 valence e − M e − the cation charge = the group number
15 Ions Relating Group Number to Ionic Charge for Groups 6A and 7A group 6A:X 6 valence e − + 2e − X 2− group 7A:X 7 valence e − + e − X − the anion charge = 8 – group number charge = 8 – 6 = 2 charge = 8 – 7 = 1
16 Table 3.1
17 Ions Ions Formed by the Main Group Elements
18 Ions Metals with Variable Charge
19 Sample Problem 3.4 Question Use the group number to determine the charge on an ion derived from each element: (a) barium (b) sulfur Solution (a)Barium (Ba) group 2A cation Ba 2+ (b)Sulfur (S) group 6A anion S 2-
20 Common Ions in the Human Body
21 Ionic Compounds Formulas for Ionic Compounds The sum of the charges in an ionic compound must be zero overall.
22 Ionic Compounds Formulas for Ionic Compounds
23 Ionic Compounds HOW TO Write a Formula for an Ionic Compound Step  Identify which element is the cation and which is the anion. Metals form cations and nonmetals form anions. Use the group number of a main group element to determine the charge. KClCaO metalnonmetal metal nonmetal group 1Agroup 7Agroup 2Agroup 6A K+K+ Cl − Ca 2+ O2−O2−
24 Ionic Compounds HOW TO Write a Formula for an Ionic Compound Step  Determine how many of each ion type is needed for an overall charge of zero. K+K+ Cl − Ca 2+ O2−O2− One of each ion is needed to balance charge. When the cation and anion have the same charge, only one of each is needed. +KCl +CaO zero charge
25 Ionic Compounds HOW TO Write a Formula for an Ionic Compound When the cation and anion have different charges, use the ion charges to determine the number of ions of each needed. Ca 2+ Cl − A +2 charge means 2 Cl − anions are needed. A -1 charge means 1 Ca 2+ cation is needed. Ca 2+ Cl − +CaCl 2 2 Cl − for each Ca 2+
26 Ionic Compounds HOW TO Write a Formula for an Ionic Compound Step  To write the formula, place the cation first and then the anion, and omit charges. KCl CaO CaCl 2 Use subscripts to show the number of each ion needed to have a zero overall charge. When no subscript is written, it is assumed to be “1.”
27 Naming Ionic Compounds Naming Cations Main group cations are named for the element from which they are formed. Na + K+K+ Ca 2+ Mg 2+ sodiumpotassium calcium magnesium
28 Naming Ionic Compounds Naming Cations Systematic name: Follow the name of the cation by a Roman numeral in parentheses to indicate its charge. Fe 2+ iron(II) Fe 3+ iron(III) Other cations can be named two ways: Common name: Use suffix “-ous” for the cation with a smaller charge and suffix “-ic” for the cation with a higher charge. ferrous ferric Fe 2+ Fe 3+
29 Naming Ionic Compounds
30 Naming Ionic Compounds Naming Anions Anions are named by replacing the ending of the element name by the suffix “-ide.”
31 Naming Ionic Compounds Compounds of Main Group Metals Name the cation and then the anion. Do not specify the charge on the cation. Do not specify how many ions of each type are needed to balance charge. Na + sodium F − fluoride NaF sodium fluoride + Mg 2+ magnesium Cl − chloride MgCl 2 magnesium chloride (not magnesium dichloride) +
32 Naming Ionic Compounds Compounds of Metals with a Variable Charge HOW TO Name an Ionic Compound That Contains a Metal with Variable Charge Example Step  Give the name for CuCl 2. Determine the charge on the cation. CuCl 2 2 Cl − anions = −2 total negative charge Cu cation must have a +2 charge to make the overall charge zero
33 Naming Ionic Compounds Compounds of Metals with a Variable Charge HOW TO Name an Ionic Compound That Contains a Metal with Variable Charge Step  Name the cation and the anion. SystematicCommon cation is named one of two possible ways: Cu 2+ copper(II) cupric anion changes ending of element name to “-ide” Cl − chloride
34 Naming Ionic Compounds Compounds of Metals with a Variable Charge HOW TO Name an Ionic Compound That Contains a Metal with Variable Charge Step  Write the name of the cation first, then the anion. Answer = copper(II) chloride or cupric chloride
35 Naming Ionic Compounds Writing a Formula from the Name HOW TO Derive a Formula from the Name of an Ionic Compound Example Write the formula for tin(IV) oxide. Step  Identify the cation and anion and determine their charges. tin(IV) oxide Sn 4+ O2−O2− Sn O
36 Naming Ionic Compounds Writing a Formula from the Name HOW TO Derive a Formula from the Name of an Ionic Compound Step  Balance charges. Sn 4+ O2−O2− Two −2 anions are needed for each +4 cation. Step  Write the formula with the cation first, and use subscripts to show how many of each ion is needed to have zero overall charge. final answer = SnO 2
38 Figure 3.4
39 Physical Properties of Ionic Compounds Ionic compounds are crystalline solids that have very high melting points (NaCl = 801 o C) and extremely high boiling points (NaCl = 1413 o C). When ionic compounds dissolve in water, they separate into cations and anions. The resulting aqueous solutions conduct an electric current. NaCl + water solution
40 Polyatomic Ions A polyatomic ion is a cation or anion that contains more than one atom.
41 Polyatomic Ions Writing Formulas for Ionic Compounds with Polyatomic Ions When a cation and anion of equal charge combine, only one of each ion is needed. Na + NO 2 − +NaNO 2 zero overall charge Ba 2+ SO 4 2− +BaSO 4 zero overall charge
42 Polyatomic Ions Writing Formulas for Ionic Compounds with Polyatomic Ions When a cation and anion of unequal charge combine, use the ionic charges to determine the relative number of each ion that is needed. Mg 2+ OH − +Mg(OH) 2 zero overall charge +2 charge means 2 OH − anions are needed. −1 charge means 1 Mg 2+ anion is needed.
43 Polyatomic Ions Naming Ionic Compounds with Polyatomic Ions Name the cation and then the anion. Do not specify the charge on the cation. Do not specify how many ions of each type are needed to balance charge. The same rules are followed for naming standard ionic compounds: NaHCO 3 Al 2 (SO 4 ) 3 sodium bicarbonate or sodium hydrogen carbonate aluminum sulfate
44 Normal bone Brittle bone Bone is composed largely of an ionic solid Ca 10 (PO 4 ) 6 (OH) 2 called hydroxyapatite.