Nowoczesne spojrzenie na konfiguracje elektronowe i układ okresowy pierwiastków, czyli o efektach relatywistycznych w chemii

The article describes in an accessible, conceptual way various types of relativistic effects, which are an important part of modern chemical education, practically absent in textbooks, however allowing for a better understanding of the properties of chemical elements and their compounds. This description was preceded by a concise non-relativistic characterization of electrons in multi-electron atoms, in terms of radial probability densities, in order to explain the dependence of electron energies on the principal (n) and orbital (l) quantum numbers. The results of recent quantum chemical calculations are discussed, which show the improved energy sequence of ns and (n-1)d orbitals in transition elements and explain the electron configurations of both neutral atoms and cations of the 3d and 4d block elements. The description of the relativistic effects begins with early Dirac concept of spin-orbit coupling as causing the splitting of the degenerate p, d and f orbitals for two sets of spinors. The role of this splitting in the stability of the respective oxidation states of the cations is discussed. Another important type of relativistic effects, confirmed only in the 1970s, operates in atoms of high nuclear charge (starting from 6. period) in which electrons move at a speed close to the speed of light. The resulting relativistic increase in the mass of the moving electron causes the stabilization of s and p orbitals, and destabilization of d and f orbitals. Representative examples of the influence of all relativistic effects on the properties of elements and their compounds are given (including mercury liquidity or the color of gold). In particular, relativistic effects specific for blocks 5d, 6p, 4f, 5f, 6d, and 7p were discussed. The possibilities of predicting further expansion of the periodic table with elements up to the atomic number of about 170 are outlined, based on taking into account both the relativistic effects for electrons and the stability of superheavy atomic nuclei. The article is addressed to chemists of all branches of this discipline.