How is vsepr used to classify molecules?

1 Answer
Jan 1, 2014

VSEPR is used together with Lewis structures to determine the shapes of molecules.

The Lewis structure gives you the number of bonding electron pairs and lone pairs that surround a molecule's central atom. These determine the shape of the molecule according to the following principles:

  1. You must determine the steric number — the number of bonding pairs and lone pairs about the central atom. The repulsion between valence electron pairs on the central atom determines the shape of the molecule.
  2. Lone pairs repel more than bonding pairs.

Each steric number has its own electron pair geometry. The number of lone pairs then determines the molecular shape.