CHM 401

 

VSEPR : Valence Shell Electron Pair Repulsion model

VSEPR uses Lewis dot structures and a simple electrostatic model to predict molecular geometries

1. Write the Lewis dot structure with the lowest possible formal charges.

2. Determine the total number of bonds+lone pairs around the center of interest.

(note : sb = db = tb in this count)

3. Distribute these electrons according to the following scheme (based on minimizing repulsion):

count

distribution geometry

shape

2

linear

3

trigonal

4

tetrahedral

5

trigonal bipyramid

6

octahedral

4. Add in atoms and assign lone pairs to minimize total repulsions

lp-lp > lp-bp > bp-bp (tb > db > sb)