Relating Bond Orders and Bond Energies to Ionization Energies and Electron Affinities: A Quantitative Approach

In General Chemistry, students are often asked to predict changes in bond energy based on changes in bond order when electrons are either added to or removed from a molecule. This gives a qualitative understanding of the correlation between bond order and bond energy, but it is not descriptive of the actual changes in the bond energies involved. In this paper, we present a quantitative approach to this prediction based on ionization energy, electron affinity, and conservation of energy (or Hess’ law). These are all concepts that are familiar to General Chemistry students. With this quantitative approach, we can more fully illustrate how bonding and antibonding electrons contribute to bond strength and better relate these to ionization energies and electron affinities. Multiple examples are given to illustrate a range of possibilities and to compare variations of bond energies.