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

C

H

H

H

H methane, CH4

Bonds are all evenly spaced electrons

109.5°

C

H

H

H

H

Tetrahedral

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 NH H

H

OH H.. ..

..

109.5° (109.5°) 109.5° (107°) 109.5° (105°)

water, H2O

C

H

H

H

H NH H

H

OH H.. ..

..

H

CH H

HN

H HH

OH H

Bent

2 unshared pairs of e’s at top of O repel bonds and force them to bend

molecular geometry.

H2CO

H

H

C O

molecular geometry.

H2CO C O

H

H

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

Molecule Lewis Structure Number of electron pairs

BeCl2

BF3

SHAPE

2

3

Linear

Trigonal Planar

SL Content

HL Content

HL Content