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Valence
Shell
Electron
Pair
Repulsion
Theory
Planar triangular
Tetrahedral
Trigonal pyramidal
Bent
VSEPR theory assumes that the shape of a molecule is determined by the repulsion of electron pairs.
Molecular Shape
VSEPR Theory• Based on Electron Dot (Lewis structures)
• Theory predicts shapes of compounds• abbreviated VSEPR
• VSEPR (pronounced “vesper”) stands for Valence Shell Electron Pair Repulsion
• VSEPR predicts shapes based on electron pairs repelling (in bonds or by themselves)
• Electrons around central nucleus repel each other. So, structures have atoms maximally spread out
VSEPR overview• Each shape has a name
(you will have to know these)• Names of Shapes:
• tetrahedral
• trigonal pyramidal
• Bent
• Linear
• trigonal planar
Triangular PlanarTetrahedral
Trigonal pyramidalLinear
Bent
Models
NH H
H
C
H
H
H
H
Less repulsion between the bonding pairs of electrons
.
.ammoni
a
NH3
. ...
.
.
Trigonal Pyramidal
C H
H
H
H
CH
H
HH
CH
H
HH
Methane (CH4) simple hydrocarbon. Shape is not planar but tetrahedral.
tetrahedral
Molecule Lewis Structure Number of electron pairs
CH4
NH3
SHAPE
Tetrahedral
Trigonal Pyramidal
4
4
(3 shared
1 lone pair)
Molecule Lewis Structure Number of electron pairs
H2O
CO2
SHAPE
Bent
4
(2 shared 2 lone pairs)
4
Linear