VSEPR – Valence-shell Electron-pair Repulsion Theory
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Shows 3-D shapes of molecules.
Uses the fact that bonding and non-bonding electron pairs repel each other.
Electron pairs are placed as far as possible from each other.
Non-bonding pairs are larger than bonding pairs.
Electron pairs are called Electron Domains.
Single, double or triple bonds are counted as only 1 Electron Domain.
We have to count the number of Electron Domains in the Lewis structure.
Electron
Domains
Electron-domain
Geometry
Bonding
Domains
Non-bonding
Domains
Molecular
Geometry
Bond
Angle
Examples
2
Linear
2
0
Linear
180o
CO2 , BeCl2, HgCl2
3
Trigonal
planar
3
0
Trigonal
planar
120o
BF3 , SO3
2
1
Bent
104.5o
NO2-1 , SO2 , O3
4
0
Terahedral
109.5o
CH4 , TiCl4, XeO4
3
1
Trigonal
pyramidal
107o
NH3 , PCl3
2
2
Bent
<107o
H2O , OF2
5
0
Trigonal
bipyramidal
90o & 120o
PCl5
4
1
Seesaw
90o & <120o
SF4
3
2
T-shaped
90o & <120o
ClF3 , BrF3
2
3
Linear
180o
XeF2
6
0
Octahedral
90o & 180o
SF6 , WCl6
5
1
Square
Pyramidal
4
2
Square planar
4
5
6
Tetrahedral
Trigonal
Bipyramidal
Octahedral
>90o & 180o
90o
BrF5 , XeOF4
XeF4