Relative AO Energies for MO Diagrams H He Li Be B C N O F Ne B C N O F Ne Na Mg Al Si P S Cl Ar Al Si P S Cl Ar 1s 2s 2p 3s 3p –19.4 eV –15.8 eV –32.4 eV –10.7 eV Photoelectron spectroscopy gives us a pretty good idea of the relative energies for AOs.