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Oxidation States and Elements’ Periodicity A View from the 7th Row on the Periodic Table

By W. H. Eugen Schwarz
Physical and Theoretical Chemistry, University of Siegen, 57068 Germany
Theoretical Chemistry Center,  Tsinghua University, 100084 Beijing, China

We draw various conclusions from results of relativistically corrected computations at density-functional up to RAS-SCF-PT2-SI/SO levels on heavy atomic systems such as [UCl6]2−, AnO4, Sg@Au12, [Sg6O19]2−, Rg2, etc. Concerning in particular the periodic table of chemical elements, we stress the fact that the Usual Order of Effective Valence Orbital Energies of Atoms in Compounds for all groups 3-18 is

1s<<  2s<2p<<  3s<3p<<  3d<4s<4p<<  4d<5s<5p<< 4f<5d<6s<6p< 5f<6d<7s<7p< …..

The large energy gaps above the np shells are the result of the orbital energy order for given nns<np<nd<<nf, which is caused by the nuclear shielding of the core electrons, and by the valence electrons’ centrifugal force ~ ℓ2. The gaps above np  pin the periodicity of the elements through the neighboring, but chemically so different groups of the halogens, noble-gases and alkali-metals. Owing to the “d and f orbital collapses” upon increasing nuclear charge and ionic charge of the atoms, the ‘true’ orbital order differs so much from the textbook order, which holds for some of the groups 1-2 elements.