Molecular Shapes from Electron Pairs

Molecular shape can be predicted from the way electron pairs arrange around a central atom. Valence shell electron-pair repulsion theory, or VSEPR theory, uses a Lewis structure to count bonding pairs and lone electron pairs. The main idea is simple: electron pairs spread out as far as possible to reduce repulsion.

The valence shell electron-pair repulsion, or VSEPR, theory assumes that electron groups involved in single bonds, multiple bonds, or lone pairs repel each other and try to stay at the maximum possible distance from each other.  

The molecular geometry is dictated by the arrangement of various electron groups around the central atom.