Orbital Hybridization and Repulsion in Structural Analogies and Fallacies

The Valence Shell Electron Pair Repulsion (VSEPR) theory is one of the most successful of the elementary ways to explain molecular geometry and deviations from the bond angles predicted for hybrid orbitals. However, it is necessary to invoke other factors to explain in a satisfactory manner the fact that the bond angle in NH 3 is 107.3o whereas that in PH3 is only 93.3o and the greatly different basicity of the molecules. Moreover, there are other simple molecules for which additional influences are involved, and they must be considered in order to explain structural features. In this report, electron repulsion and orbital hybridization are considered in explaining bond angles in hydride molecules having formulas EHn (n = 2−4) and other molecules such as X2C=O (where X = F, Cl, Br, or H). Bond strengths and other features related to molecular structure are also considered.