Energy Effects in Binary Ionic Compounds and Lattice Energy

Consider Ionic Compounds

Consider Ionic Compounds Not molecules

Consider Ionic Compounds Not molecules Have an arrangement of several ions all interacting with each other.

Consider Ionic Compounds Not molecules Have an arrangement of several ions all interacting with each other. The solid is a regular arranged pattern of ions called a crystal lattice.

LiF…….An ionic compound between lithium and fluorine

LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas 1. Li (s)  Li (g) +161 kJ/mol

LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas Li must be ionized (ionization energy) 1. Li (s)  Li (g) +161 kJ/mol 2. Li (g)  Li+ (g)+e- +520kJ/mol

LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas Li must be ionized (ionization energy) F molecules need to be broken into atoms 1. Li (s)  Li (g) +161 kJ/mol 2. Li (g)  Li+ (g)+e- +520kJ/mol 3. 1/2F2 (g)  F (g) +77 kJ/mol

LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas Li must be ionized (ionization energy) F molecules need to be broken into atoms Form F ions 1. Li (s)  Li (g) +161 kJ/mol 2. Li (g)  Li+ (g)+e- +520kJ/mol 3. 1/2F2 (g)  F (g) +77 kJ/mol 4. F (g) + e-  F- (g) -328 kJ/mol

LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas Li must be ionized (ionization energy) F molecules need to be broken into atoms Form F ions (electron affinity) The ions are highly attracted to each other…Lattice energy 1. Li (s)  Li (g) +161 kJ/mol 2. Li (g)  Li+ (g)+e- +520kJ/mol 3. 1/2F2 (g)  F (g) +77 kJ/mol 4. F (g) + e-  F- (g) -328 kJ/mol 5. Li+ + F-  LiF -1047kJ/mol

An ionic compound forms between a metal and a nonmetal Net change: kj/mol

An ionic compound forms between a metal and a nonmetal Net change: kj/mol 1. 161 2. 520 3. 77 4. -328 5. -1047 - 617 kJ/mol of LiF formed

An ionic compound forms between a metal and a nonmetal The solid formed is a regular arranged pattern of ions called a crystal lattice Net change: kj/mol 1. 161 2. 520 3. 77 4. -328 5. -1047 - 617 kJ/mol of LiF formed

An ionic compound forms between a metal and a nonmetal The solid formed is a regular arranged pattern of ions called a crystal lattice Lattice energy of LiF is -1047 kJ/mol Net change: kj/mol 1. 161 2. 520 3. 77 4. -328 5. -1047 - 617 kJ/mol of LiF formed

As LiF (or another ionic compound dissolves in water………….

As LiF (or another ionic compound dissolves in water…………. Energy must be released to pull ions apart

As LiF (or another ionic compound dissolves in water…………. Energy must be released to pull ions apart The quantity of energy released must be > or = to the lattice energy

As LiF (or another ionic compound dissolves in water…………. Energy must be released to pull ions apart The quantity of energy released must be > or = to the lattice energy Energy of hydration

Hydration of ion..dissolving Requires and interaction with the polar water molecule General rule of solubility…”Like dissolves like” Nonpolar molecules require nonpolar solvents

Lattice Energies of Alkali Metals Halides (kJ/mol) F- Cl- Br- I- Li+ 1047 853 807 757 Na+ 923 787 747 704 K+ 821 715 682 649 Rb+ 785 689 660 630 Cs+ 740 659 631 604

Lattice energy for LiF is -1047 kJ/mol….it dissolves in water Lattice Energies of Alkali Metals Halides (kJ/mol) F- Cl- Br- I- Li+ 1047 853 807 757 Na+ 923 787 747 704 K+ 821 715 682 649 Rb+ 785 689 660 630 Cs+ 740 659 631 604

Lattice energy for LiF is -1047 kJ/mol….it dissolves in water Lattice energy for MgO is -3916 kJ/mol… it does not dissolve in water Lattice Energies of Alkali Metals Halides (kJ/mol) F- Cl- Br- I- Li+ 1047 853 807 757 Na+ 923 787 747 704 K+ 821 715 682 649 Rb+ 785 689 660 630 Cs+ 740 659 631 604

Lattice energy for LiF is -1047 kJ/mol….it dissolves in water Lattice energy for MgO is -3916 kJ/mol… it does not dissolve in water Lattice energy for NaF -923kJ/mol Lattice Energies of Alkali Metals Halides (kJ/mol) F- Cl- Br- I- Li+ 1047 853 807 757 Na+ 923 787 747 704 K+ 821 715 682 649 Rb+ 785 689 660 630 Cs+ 740 659 631 604

Ion-Ion Interactions Coulomb’s law states that the energy (E) of the interaction between two ions is directly proportional to the product of the charges of the two ions (Q1 and Q2) and inversely proportional to the distance (d) between them.

Predicting Forces of Attraction Coulombs Law indicates the increases in the charges of ions will cause an increase in the force of attraction between a cation and an anion. Increases in the distance between ions will decrease the force of attraction between them.

Size of Ions

Lattice Energy M+(g) + X-(g) ---> MX(s) The lattice energy (U) of an ionic compound is the energy released when one mole of the ionic compound forms from its free ions in the gas phase. M+(g) + X-(g) ---> MX(s)

Comparing Lattice Energies Lattice Energies of Common Ionic Compounds Compound U(kJ/mol) LiF -1047 LiCl -864 NaCl -790 KCl -720 KBr -691 MgCl2 -2540 MgO -3791

Practice Determine which salt has the greater lattice energy. MgO and NaF MgO and MgS

Lattice Energy Using Hess’s Law

Electron Affinity Cl(g) + e-(g) ---> Cl-(g) Electron affinity is the energy change occurring when one mole of electrons combines with one mole of atoms or ion in the gas phase. Step 4 in diagram on the last slide. Cl(g) + e-(g) ---> Cl-(g) ΔHEa = -349 kj/mole

Calculating U Na+(g) + e-(g) ---> Na(g) -HIE1 Na(g) ---> Na(s) -Hsub Cl-(g) ---> Cl(g) + e-(g) -HEA Cl(g) ---> 1/2Cl2(g) -1/2HBE Na(s) + 1/2Cl2(g) ---> NaCl(s) Hf Na+(g) + Cl-(g) ---> NaCl(s) U U = Hf - 1/2HBE - HEA - Hsub - HIE1

Lattice energy for NaCl.