Ionic
Lewis Dot Notation
Gilbert N. Lewis
American
1902
abbreviates valence e– configuration
ns1
ns2
IA
IIA
+
IIIA
IVA
VA
VIA
••
••
••
••
••
••
DH
=
lattice energy
DHlatt =
NaCl(s)
DHfo =
Born-Haber Cycle
Born-Haber Cycle
Similar to Hess’s Law:
Why MgCl2?
1/2 Cl2(g)
DHfo =
NaCl(s)
Mg(s)
+
Cl2(g)
DHfo = ?
DHlattice
Mg(g)
2+:1–
Cl(g)
vs
Mg+(g)
1+:1–
+
Cl–(g)
Mg2+(g)
DHfo =
Born-Haber Cycle
Why not NaCl2?
AlCl3
+
Cl2(g)
DHf = ?
NaCl2(s)
like MgCl2
DHlattice
–2180 kJ
Na(g)
2 Cl(g)
Na+(g)
DHfo =
2 Cl–(g)
+
Born-Haber Cycle
o
Na2+(g)
DHlatt NaCl
–788 kJ
DHfo =
DHfo
Na(s)
DHlattice
–2422 kJ
2 Cl(g)
EA
IE1
Na+(g)
MgCl2(s)
DHdissociation
DHsublimation
Na(g)
=
Max
Fritz
Born
Haber
German
1912
••
••
+
••
••
Na(s)
Cl– (g)
VIIA
•
•
••
••
••
•B• •C• •N• O• F•
•
•
•
••
••
••
••
•
•
•
• Al • • Si • • P • S • Cl •
Na • Mg •
•
•
•
••
••
••
••
2
6
•
• Ge • • As • Se • Br • ns np
K•
•
•
•• VIIIA
•
•
••
••
••
••
• Sn • • Sb • Te • I • Xe
not for transition metals
•
•
•
••
••
ΔH
+
½ Cl2(g)
ns2np1 ns2np2 ns2np3 ns2np4 ns2np5
•
Li • Be •
Na+ (g)
Na(s)
tool that describes molecular (mostly)
+
3/2 Cl2(g)
DHfo = ?
AlCl3(s)
Al(g)
Al+(g)
DHlatt NaCl
–788 kJ
+
Al(s)
3 Cl(g)
DHlattice
–5458 kJ
Al2+(g)
2 Cl–(g)
Al3+(g)
DHf
o
+
3 Cl–(g)
=
1
Some Lattice Types
CsCl
NaCl
Drawing Good Lewis Structures
MgCl2
CaF2
1. # valence e– in atoms (± charge) must = # e– in structure ; always
2. determine connectivity: most metallic usually central; avoid small rings;
H always terminal (1 e–)
1+ 1–
1+ 1–
2+ 1–
2+ 1–
–667 kJ/mole
–788 kJ/mole
–2422 kJ/mole
–2805 kJ/mole
ZnS
AlCl3
Al2O3
3. complete octet for each atom (except H); check against #1
4. remove/add required e– in pairs from/to central atom
5. if needed, move e– pairs from outside atoms to bond with central atom
to complete octet again
6. formal charge minimized as much as possible (# and mag.)
2+ 2–
3+ 1–
3+ 2–
–3526 kJ/mole
–5458 kJ/mole
–15270 kJ/mole
Formal Charge
ve–
assigned
formal charge
7
7
0
7
6
+1
••
7
7
0
••
6
6
0
••
••
••
••
••
7
7
0
••
•• •• + •• –
F F O
•• •• ••
•• •• ••
F O F
•• •• ••
6
7
–1
assign e– in molecule to each atom:
1. lone-pair e– belong to atom
2. bonding pairs split equally
compare with ve– in atom
6. formal charge minimized as much as possible (# and mag.)
2