Chemistry 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):

countdistribution geometryshape

 

 

2linear

 

 

3trigonal

 

 

 

 

4tetrahedral

 

 

 

 

5trigonal bipyramidal

 

 

 

 

 

6octahedral

 

 

 

 

 

 

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

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

Structure Prediction using VSEPR

PF₅

TeF₄

BrF₃