VValencealence

SShellhell

EElectronlectron

PPairair

RRepulsionepulsion

TheoryTheory

Planar triangular

Tetrahedral

Trigonal pyramidal

Bent

VSEPR theory assumes that the shape of a VSEPR theory assumes that the shape of a molecule is determined by the molecule is determined by the repulsion repulsion of of electron pairs.electron pairs.

Molecular ShapeMolecular Shape

VSEPRVSEPR Theory 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 overviewVSEPR 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 or V

Models

methane, CHmethane, CH44

Bonds are all evenly spaced Bonds are all evenly spaced electrons electrons

109.5°109.5°

TetrahedralTetrahedral

Less repulsion between the bonding pairs of electronsLess repulsion between the bonding pairs of electrons

.. ammoniammoniaa

NHNH33..

..

..

Trigonal Trigonal PyramidalPyramidal

.. ....

109.5° (109.5° (109.5109.5°)°) 109.5° (109.5° (107107°)°) 109.5° (109.5° (104.5°)104.5°)

water, Hwater, H22OO

.. ....

Bent or VBent or V

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

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 or V

4

(2 shared 2 lone pairs)

2

Linear

Molecule Lewis Structure Number of electron pairs

BeCl2

BF3

SHAPE

2

3

Linear

Trigonal Planar