Steric
Number (SN) = (atoms
attached to central atom) + (lone pairs on central atom)
|
SN |
Electron
Pair Arrangement |
Molecular
Shapes |
Examples |
|
2 |
sp |
linear
180° |
AX2 linear |
BeCl2, CO2 |
|
3 |
sp2 |
trigonal planar
120° |
AX3 trigonal planar
AEX2 bent |
BCl3, CH3+
SnCl2, NO2- |
|
4 |
sp3 |
tetrahedral
109.5° |
AX4 tetrahedral
AEX3 pyramidal
AE2X2 bent |
CH4, PO43-
NH3, ClO3-
H2O, SeF2 |
|
5 |
sp3d |
trigonal
bipyramidal
120° & 90° |
AX5 trig bipyramidal
AEX4 "see saw"
AE2X3 T-shaped
AE3X2 linear |
PF5, SeCl5+
SF4, BrF4+
ClF3, XeO32-
XeF2, ICl2- |
|
6 |
sp3d2 |
octahedral
90° |
AX6 octahedral
AEX5 square pyramidal
AE2X4 square planar |
SF6, PCl6-
BrF5, SF5-
XeF4, IF4- |
(A = central atom, X = terminal
atom, E = lone pair)
In trigonal bipyramid structures, lone
e- pairs adopt equatorial positions (e).
Order of repulsions: Lp
- Lp > Lp - Bp >> Bp - Bp.
Combined with electronegativity
concept, VSEPR predicts polarity of molecules.
|
