The Connections Between Electron Configuration and the Variations of the Oxidation State

Abstract

The ionization energy of gaseous ions, strongly increasing as a function of the charge, is compensated with a remarkable precision in compounds and aqua ions. The available oxidation states in aqueous solution correspond to actual ionization energies not below 30 kK and the electron affinity not above 50 kK (1 kK = 1000 cm^-1). The chemical transition groups start at a higher atomic number than the spectroscopic ones; the average oxidation number goes through a distinct maximum except in the case of the lanthanides. The effects of interelectronic repulsion, the polarisability and the back-bonding to the ligands are discussed, as well as the definition of the spectroscopic oxidation state as contrasted to fractional atomic charges.