CHAPTER 3 Ionic Compounds. General, Organic, & Biological Chemistry Janice Gorzynski Smith

Transcription

1 CHAPTER 3 Ionic Compounds General, Organic, & Biological Chemistry Janice Gorzynski Smith

2 CHAPTER 3: Ionic Compounds Learning Objectives: q Octet Rule & Predicting ionic Charges q Ionic Bonds q Formation of cations by metals q Formation of anions by nonmetals q Metals capable of forming multiple charges q Formation of electronically neutral ionic compounds q Polyatomic ions q Naming Ionic Compounds q Properties of Ionic Compounds q High Melting & Boiling Points q Conductive aqueous solutions 2

3 Bonding Definition Bonding is the joining of two atoms in a stable arrangement. Elements will gain, lose, or share electrons to reach the electron configuration of the noble gas closest to them in the periodic table. There are two different kinds of bonding: 1. Ionic bonds result from the transfer of electrons from one element to another. 2. Covalent bonds result from the sharing of electrons between two atoms. 3

4 Bonding Definition Li F 4

5 Bonding Ionic Bonds vs Covalent Bonds Ionic bonds form between: A metal (left side periodic table) A nonmetal (right side periodic table) Covalent bonds are formed when two nonmetals combine, or when a metalloid bonds to a nonmetal. 5

6 Ions Cations Cations are positively charged ions. A cation has fewer electrons (e ) than protons. the sodium atom the sodium ion 6

7 Ions Anions Anions are negatively charged ions. An anion has more e than protons. the chlorine atom the chlorine ion 7

8 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. octet = 8 valence e 8

9 Ions Charge as Determined by Periodic Group the cation charge = the group number group 1A: M 1 valence e M + + e group 2A: M 2 valence e M e group 3A: M 3 valence e M e 9

10 Ions Charge as Determined by Periodic Group the anion charge = 8 group number group 6A: X 6 valence e + 2e X 2 charge = 8 6 = 2 group 7A: X 7 valence e + e X charge = 8 7 = 1 10

11 Ions Main Group Ions 11

12 Ions Metals with Variable Charges 12

13 Ions Biologically Relevant Ions hkp:// 13

14 Ionic Compounds Definition & Solid Structure The sum of the charges in an ionic compound must be zero overall. Ions will arrange to maximize anion-cation attractions and minimize anion-anion and cation-cation repulsions 14

15 Ionic Compounds Charge Balance 15

16 Ionic Compounds Formula for Ionic Compounds HOW TO Write a Formula for an Ionic Compound Step [1] Step [2] Identify which element is the cation and which is the anion. Determine how many of each ion type is needed for an overall charge of zero. à When the cation and anion have different charges, use the ion charges to determine the number of ions of each needed. Step [3] To write the formula, place the cation first and then the anion, and omit charges. 16

17 Ionic Compounds Criss-Cross Rule Criss-cross rule Make magnitude of charge on one ion into subscript for other When doing this, make sure that subscripts are reduced to lowest whole number. Al 3+ O 2 Al 2 O 3 17

18 Naming Main Group Cations Main group cations are named for the element from which they are formed. Na + K + Ca 2+ Mg 2+ sodium potassium calcium magnesium 18

19 Naming Multiple Charge 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) Common name: Use suffix -ous for the cation with a smaller charge and suffix -ic for the cation with a higher charge. Fe 2+ Fe 3+ ferrous ferric 19

20 Naming Anions Anions are named by replacing the ending of the element name by the suffix -ide. 20

21 Naming Ionic Compounds Name the cation and then the anion. Do not specify the charge on the ion. 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 21

22 Naming Ionic Compounds HOW TO Name an Ionic Compound Step [1] Determine the charge on the cation. Step [2] Name the cation and the anion à If the cation could be multiple charges indicate the charge with roman numerals or with a ous / -ic suffix. Step [3] Write the name of the cation first then the name of the anion 22

23 Naming Ionic Compounds HOW TO Derive the Formula from the Name of an Ionic Compound Step [1] Identify the cation and the anion. Step [2] Step [3] Determine the charge on the cation and anion. Balance the charges. Step [4] Write the formula with the cation first and use subscripts to communicate charge balance. 23

24 Properties Physical Properties of Ionic Compounds Ionic compounds are crystalline solids with very high melting and boiling points. When ionic compounds dissolve in water, they separate into cations and anions, increasing the conductivity of the solution. + à NaCl water solution

25 Polyatomic Ions Definition A polyatomic ion is a cation or anion that contains more than one atom. The multiple atoms are held together with covalent bonds The molecule has an overall charge associated with it. 25

26 Polyatomic Ions Writing Formula 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 2 4 BaSO 4 zero overall charge 26

27 Polyatomic Ions Writing Formula 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 charge means 2 OH anions are needed. + OH Mg(OH) 2 1 charge means 1 Mg 2+ anion is needed. zero overall charge 27

28 Polyatomic Ions Naming Ionic Compounds The same rules are followed for naming standard ionic compounds: Name the cation and then the anion. Do not specify the charge on the ions. Do not specify how many ions of each type are needed to balance charge. Use ite suffix if 1 or less Oxygen atoms in anion Use ate suffix if more Oxygen atoms in anion Use bi- prefix or write hydrogen if H part of anion NaHCO 3 Al 2 (SO 4 ) 3 sodium bicarbonate aluminum sulfate 28