Molybdenum (Mo) exists with the electron confirguration (Kr]5544d5 , this is not the ground state configuration. This is similar to what we studied with chromium. Why. does a configuration like this sometimes seem to be preferred? It is more stable because it leaves 5s almost empty. It is more stable because the orbitals in the valence shell are all half full. An electron is promoted from 5 to 4d because 4d is lower in energy. It is an excited state and only exists for a short amount of time