Conditions for stability of oxidation states derived from photo‐electron spectra and inductive quantum chemistry

The 315 oxidation states in non‐metallic, non‐catenated compounds are arranged according to their Kossel number of electrons K in 81 isoelectronic series. The profound differences between the four categories (the 4f, the 5f and the d groups, and the other elements) are analyzed and compared with ionization energies I of loosely bound electrons obtained from photo‐electron spectra, and their slope (dI/dZ). It seems difficult, but not impossible, still to prepare a few new oxidation states. The examples argon(II), copper(IV), silver(V), thulium(IV), mercury(III) and francium(V) are discussed.