Ch. 13: Bonding Formation of Binary Ionic Compound

Lattice Energy  change in energy that takes place when separate gas ions come together to make an ionic solid M + (g) + X - (g)  MX(s)  always has a negative sign because it is an exothermic process

Lattice Energy  k depends on the structure of solid and electrons configuration  process becomes more exothermic as the ionic charges increase and as the distances between ions decrease

Formation of Ionic Solid 1. Sublimination of solid metal ∆H sub Li(s)  Li(g)161 kJ Li(s)  Li(g)161 kJ 2. Ionization of gaseous metal atoms 1 st Ionization Energy Li(g)  Li + (g) + e kJ Li(g)  Li + (g) + e kJ 3. Dissociation of nonmetal molecules Bond Energy ½F 2 (g)  F(g)77 kJ ½F 2 (g)  F(g)77 kJ

Formation of Ionic Solid 4. Formation of nonmetal ion Electron Affinity F(g) + e -  F - (g)-328 kJ F(g) + e -  F - (g)-328 kJ 5. Formation of solid from gaseous ions Lattice Energy Li + (g) + F - (g)  LiF(s)-1047 kJ Li + (g) + F - (g)  LiF(s)-1047 kJ Li(s) + ½F 2 (g)  LiF(s)-617 kJ

Formation of Ionic Solid  extremely exothermic because of the large lattice energy  ions are packed together so that attraction between oppositely charged ions is maximized attraction between oppositely charged ions is maximized repulsion between similarly charges ions is minimized repulsion between similarly charges ions is minimized

Example  Determine ∆H° for LiBr Li(s) + ½Br 2 (g)  LiBr(s)  Given: Ionization Energy of Li = 520 kJ/mol Ionization Energy of Li = 520 kJ/mol Electron Affinity for Br = -324 kJ/mol Electron Affinity for Br = -324 kJ/mol ∆H sub for Li = +161 kJ/mol ∆H sub for Li = +161 kJ/mol Lattice Energy = -787 kJ/mol Lattice Energy = -787 kJ/mol Bond Energy of Br 2 = 193 kJ/mol Bond Energy of Br 2 = 193 kJ/mol

Example 1. Sublimination of solid metal ∆H sub Li(s)  Li(g)161 kJ Li(s)  Li(g)161 kJ 2. Ionization of gaseous metal atoms 1 st Ionization Energy Li(g)  Li + (g) + e kJ Li(g)  Li + (g) + e kJ 3. Dissociation of nonmetal molecules Bond Energy ½Br 2 (g)  Br(g) ½(193 kJ) ½Br 2 (g)  Br(g) ½(193 kJ)

Example 4. Formation of nonmetal ion Electron Affinity Br(g) + e -  Br - (g)-324 kJ Br(g) + e -  Br - (g)-324 kJ 5. Formation of solid from gaseous ions Lattice Energy Li + (g) + Br - (g)  LiBr(s)-787 kJ Li + (g) + Br - (g)  LiBr(s)-787 kJ Li(s) + ½Br 2 (g)  LiBr(s)-334 kJ

Ch. 13 Bonding Partial Ionic Character of Covalent Bonds

Ionic Character  no completely (100%) ionic bonds  ionic character increases as difference in electronegativity increases

Ionic Compounds  > 50%  conducts electric current when melted  polyatomic ions contain covalent bonds contain covalent bonds form ionic bonds with other ions form ionic bonds with other ions

Example  Which compound in each of the pairs has the most exothermic lattice energy? NaCl, KCl NaCl, KCl LiF, LiCl LiF, LiCl Mg(OH) 2, MgO Mg(OH) 2, MgO Fe(OH) 2, Fe(OH) 3 Fe(OH) 2, Fe(OH) 3 NaCl, Na 2 O NaCl, Na 2 O MgO, BaS MgO, BaS size charge size