212
8 Models of Chemical Bonding and “Empirical” Methods
Table 8.3 Electron-pair arrangements and the geometry of AX n E m molecules a
Class a AX m E n Number of
pairs m +
n
Number
m of bonds
Arrangement Shape
Bond
angle
Examples
AX 2
2
2
Linear
Linear
180
CO 2 , HCN
AX 3
3
3
Equilateral
triangular
Triangle
120
BF 3
AX 2 E
3
2
V-shape
SO 2
AX 4
4
4
Tetrahedral
Tetrahedral
109°
28
CH 4
AX 3 E
4
3
Triangular
pyramidal
NH 3
AX 2 E 2
4
2
V-shape
H 2 O
AX 5
5
5
Trigonal
bipyramidal
Trigonal
bipyramid
120°
and 90°
PCl 5
AX 4 E
5
4
Disphenoidal
SF 4
AX 3 E 2
5
3
T-shaped
ClF 3
AX 2 E 3
5
2
Linear
XeF 2
AX 6
6
6
Octahedral
Octahedral
90°
SF 6
AX 5 E
6
5
Square
pyramidal
BrF 5
AX 4 E 2
6
4
Square planar
XeF 4
a A = central atom, X = ligand, E = lone pair
Fig. 8.2 Arrangements of the electron pairs on the surface of a sphere
8 Models of Chemical Bonding and “Empirical” Methods
Table 8.3 Electron-pair arrangements and the geometry of AX n E m molecules a
Class a AX m E n Number of
pairs m +
n
Number
m of bonds
Arrangement Shape
Bond
angle
Examples
AX 2
2
2
Linear
Linear
180
CO 2 , HCN
AX 3
3
3
Equilateral
triangular
Triangle
120
BF 3
AX 2 E
3
2
V-shape
SO 2
AX 4
4
4
Tetrahedral
Tetrahedral
109°
28
CH 4
AX 3 E
4
3
Triangular
pyramidal
NH 3
AX 2 E 2
4
2
V-shape
H 2 O
AX 5
5
5
Trigonal
bipyramidal
Trigonal
bipyramid
120°
and 90°
PCl 5
AX 4 E
5
4
Disphenoidal
SF 4
AX 3 E 2
5
3
T-shaped
ClF 3
AX 2 E 3
5
2
Linear
XeF 2
AX 6
6
6
Octahedral
Octahedral
90°
SF 6
AX 5 E
6
5
Square
pyramidal
BrF 5
AX 4 E 2
6
4
Square planar
XeF 4
a A = central atom, X = ligand, E = lone pair
Fig. 8.2 Arrangements of the electron pairs on the surface of a sphere