VSEPR Theory

Valence Shell Electron Repulsion (VSEPR) Theory: a theory that the shape of a molecule is determined by the repulsion between electrons in the bonds and unshared pairs of the atoms.

Electrons are all negatively charged, so they repel each other. Valence electrons exist in two places:

  • unshared electrons (in pairs), attached to only one atom

  • as part of a covalent bond (shared pair of electrons) between two atoms

The VSEPR shape of the molecule is the shape that occurs when all of these “clouds” of electrons are as far apart as possible

The Lewis structure of a molecule represents the structure in 2 dimensions. The VSEPR shape is the 3-dimensional equivalent.

Table of VSEPR Shapes

Electron Clouds

Bond Atoms

Lone Pairs

Hybridization

Bond Angle

Picture

VSEPR Shape

4

4

0

sp3

109.5°

tetrahedral

4

3

1

sp3

107.5°

trigonal pyramidal

4

2

2

sp3

104.5°

bent

3

3

0

sp2

120°

trigonal planar

3

2

1

sp2

118°

bent

2

2

0

sp

180°

linear

/

*Note: Even though tetrahedral, trigonal pyramidal and bent can have four electron groups (tetrahedral EG), they experience different bond angles because unbonded pairs repel more strongly than bonded electrons.

Table of Expanded VSEPR Shapes

Electron Clouds

Bond Atoms

Lone Pairs

Hybridization

Bond Angle

Picture

VSEPR Shape

6

6

0

d2sp3

90°

octahedral

6

5

1

d2sp3

90° & 180°

square pyramidal

6

4

1

d2sp3

90° & 180°

square planar

6

3

3

d2sp3

90° & 180°

T-shaped

6

2

4

d2sp3

180°

linear

5

5

0

dsp3

90° & 120°

trigonal bipyramidal

5

4

1

dsp3

90° & 120°

seesaw

5

3

2

dsp3

90° & 180°

T-shaped

5

2

3

dsp3

180°

linear