Periodic table from the Baruton perspective: Some anomalies and spin correlation effect

In this study, we have looked the periodic table from the Barut’s point of view and discussed the deviations from the Madelung rule. Expected, observed and computed total energies (Hartree-Fock and Gaussian) are given for two different (one for expected and the other one is observed) configurations of the Cr atom. The data shows that preferred electronic configuration for the Cr is 4s13d5 not 4s23d4 as dictated by the Madelung rule. This event may be due to the spin correlation effect which is closely related to the Hund’s rule.

Recent attempts to change the periodic table

The article concerns various proposals that have been made with the aim of improving the currently standard 18-column periodic table. We begin with a review of 8-, 18- and 32-column formats of the periodic table. This is followed by an examination of a possible, although rather impractical, 50-column table and how it could be used to consider the changes to the periodic table that have been predicted by Pyykkö in the domain of superheavy elements. Other topics reviewed include attempts to derive the Madelung rule as well as an analysis of what this rule actually provides. Finally, the notion of an ‘optimal’ periodic table is discussed in the context of recent work by philosophers of science who have examined the nature of classifications in general, as well as the notion of natural kinds. The article takes an unapologetically philosophical approach rather than focusing on specific data concerning the elements. Nevertheless, some pragmatic issues and educational aspects of the periodic table are also examined. This article is part of the theme issue ‘Mendeleev and the periodic table’.

Spin-orbital exclusion principle and the periodic system

Groups of electrons, radial with respect to the atomic nucleus and with the same value of the orbital quantum number and the same number on the subshell, are considered. A spin-orbital exclusion principle is established, regulating the spin value distribution on the subshells with the same value of the orbital number. According to this principle, all subshells are divided into positive and negative ones, depending on the direction of the spin of their first electron. It is found that, in the real sequence of the appearance of new subshells, a spin-orbital periodicity takes place, which develops in cycles consisting of two periods that are mirror-symmetric to each other in the direction of the spin of their electrons. Moreover, atomic number of any period is equal to the sum of the principal and orbital quantum numbers of its subshells, and this can serve as an explanation for the Madelung rule. It is demonstrated that Mendeleev’s chemical periodicity lags behind the spin-orbital periodicity by two elements and repeats its structure. From these positions, the absence of a pair in the first period of Mendeleev’s table and the pairing of all its other periods are explained. Based on the obtained results, an eight-period table of elements, the prototype of which being Janet’s left-step table, is compiled and briefly described.

On the Madelung Rule

Can chemistry be reduced to physics? Eric Scerri argues that philosophers of science have done chemistry a disservice in neglecting the field that pulls the sciences together.