Valance bond theory

Although the valance bond theory can t be used to fully describe metals and was later replaced using molecular orbital theory (Chapter 6), its development was an important step in chemistry research nonetheless. 

The rules and principles of molecular geometry accurately predict the shapes of simple molecules such as methane (CH4), water (H2O), or ammonia (NH3). As molecules become increasingly complex, however, it becomes very difficult, but not impossible, to predict and describe complex geometric arrangements of atoms. The number of bonds between atoms, the types of bonds, and the presence of lone electron pairs on the central atom in the molecule critically influence the arrangement of atoms in a molecule. In addition, use of valance shell electron pair repulsion theory (VSEPR) allows chemists to predict the shape of a molecule. 

VSEPR therory—The valance shell electron pair repulsion theory (VSEPR) is a theory of electron spacing and distribution used to predict bond angles in a molecule. 

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