AP: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)
kJ/mol
+161
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)
kJ/mol
+161
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
1. Li (s)  Li (g)
kJ/mol
+161
Li must be ionized (ionization
energy)
F molecules need to be broken into
atoms
2. Li (g)  Li+ (g)+e- +520kJ/mol
3. 1/2F2 (g)  F (g)
kJ/mol
+77
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)
kJ/mol
+161
2. Li (g)  Li+ (g)+e- +520kJ/mol
3. 1/2F2 (g)  F (g)
kJ/mol
4. F (g) + e-  F- (g)
+77
-328 kJ/mol
LiF…….An ionic compound between
lithium and fluorine
Li (s) + ½ F2 (g)  LiF (s)
1. Li (s)
Li must be ionized (ionization energy)
2. Li (g)  Li+ (g)+e- +520kJ/mol
Li must be converted to a gas
F molecules need to be broken into
atoms
Form F ions (electron affinity)
The ions are highly attracted to each
other…Lattice energy
 Li (g)
+161 kJ/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.
2.
3.
4.
5.
161
520
77
-328
-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.
2.
3.
4.
5.
161
520
77
-328
-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.
2.
3.
4.
5.
161
520
77
-328
-1047
- 617 kJ/mol of LiF
formed
Born-Haber Cycle
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)
FCl- 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 -  Lattice Energies of Alkali
1047 kJ/mol….it
Metals Halides (kJ/mol)
dissolves in water
FCl- 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 -  Lattice Energies of Alkali
1047 kJ/mol….it
Metals Halides (kJ/mol)
dissolves in water
FCl- Br- I Li+ 1047 853 807 757
+ 923
Na
787 747 704
• Lattice energy for MgO
+ 821

K
715 682 649
is -3916 kJ/mol… it
+ 785
Rb
689 660 630
does not dissolve in
+ 740
Cs
659 631 604
water
 Lattice energy for LiF is  Lattice Energies of Alkali
-1047 kJ/mol….it
Metals Halides (kJ/mol)
dissolves in water
FCl- Br- I Li+ 1047 853 807 757
 Lattice energy for MgO
Na+ 923 787 747 704
is -3916 kJ/mol… it
 K+ 821 715 682 649
does not dissolve in
Rb+ 785 689 660 630
water
Cs+ 740 659 631 604
 Lattice energy for NaF
 -923kJ/mol
Size of Ions
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.
(Q1Q 2 )
E 
d
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.
Lattice Energy
• 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)
k(Q1Q2 )
U=
d
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