Trends in Bond Dissociation Energies for the Homolytic Cleavage of Successive Molecular Bonds

The students in our physical chemistry course pointed out an interesting trend in the bond dissociation energies (BDEs) of successive homolytic cleavages of hydrogens from methane and water. Namely, while there is an increase in BDE from CH4 to CH3, there is a decrease in BDE from H2O to OH. In order to explain this trend, we employed a theoretical approach that could be used in an undergraduate setting. We compare our theoretical results with experimental and highly accurate theoretical values readily available in the literature. Having validated our theoretical approach, we use equilibrium molecular structure as evidence of the change in dominating attraction and repulsion effects of the central atom nucleus and nonbonding electrons and explain the anomaly in BDEs in undergraduate chemistry terms.