Understanding Periodic and Non-periodic Chemistry in Periodic Tables

Abstract

The chemical elements are the “conserved principles” or “kernels” of chemistry that are retained when substances are altered. Comprehensive overviews of the chemistry of the elements and their compounds are needed in chemical science. To this end, a graphical display of the chemical properties of the elements, in the form of a Periodic Table, is the helpful tool. Such tables have been designed with the aim of either classifying real chemical substances or emphasizing formal and aesthetic concepts. Simplified, artistic, or economic tables are relevant to educational and cultural fields, while practicing chemists profit more from “chemical tables of chemical elements.” Such tables should incorporate four aspects: (i) typical valence electron configurations of bonded atoms in chemical compounds (instead of the common but chemically atypical ground states of free atoms in physical vacuum); (ii) at least three basic chemical properties (valence number, size, and energy of the valence shells), their joint variation across the elements showing principal and secondary periodicity; (iii) elements in which the (sp)8, (d)10, and (f)14valence shells become closed and inert under ambient chemical conditions, thereby determining the “fix-points” of chemical periodicity; (iv)peculiar elements at the top and at the bottom of the Periodic Table. While it is essential that Periodic Tables display important trends in element chemistry we need to keep our eyes open for unexpected chemical behavior in ambient, near ambient, or unusual conditions. The combination of experimental data and theoretical insight supports a more nuanced understanding of complex periodic trends and non-periodic phenomena.

Electronic Structure and Spectroscopic Properties of Group-7 Tri-Oxo-Halides MO3X (M = Mn–Bh, X = F–Ts)

“…The highest OS of the atoms in the periodic tables varies in a wavy manner, with two maxima along periods of 18 elements (namely, near the middle and the end of the periods) and with two minima in between . The intermediate minimum at OS = +2 occurs in group 12 for the zinc elements (Zn, Cd, Hg). , Hg and Eka-Hg = Cn are border cases with higher OS values being possible under more or less exotic conditions, thereby breaking the periodic rule at the bottom of the table. , The highest OS of an element depends on two points: the number of valence-active electrons available energetically above the chemically inactive core shells, and the conditions to activate the electrons and transfer them (partially) to the ligands. The covalent electron sharing or the ionic charge transfer depends also on the core and valence orbital radii, i.e., on the overlap options. − …”

“…Oxidation state (OS) is one of the most basic and useful, though fuzzy, concepts in the chemistry of elements and a fundamental criterion for their classification into similarity groups. − The highest OS values were the primary parameters for the arrangement of the elements in the early periodic tables, designed by Meyer and by Mendeleev in the 1860s. − The OS of an atom (or a group of atoms) in a compound is defined through the combination of experimental observations and theoretical model descriptions; namely, first, one draws a Lewis formula that should realistically describe the most important electronic aspects of chemical bonding in this compound, and then, the bonding pairs between two different atoms are assigned to the more electronegative one. , Obviously, the definition of OS must not be mixed up with the definition of effective charges …”

“…15,16 Hg and Eka-Hg = Cn are border cases with higher OS values being possible under more or less exotic conditions, thereby breaking the periodic rule at the bottom of the table. 11,17 The highest OS of an element depends on two points: the number of valence-active electrons available energetically above the chemically inactive core shells, and the conditions to activate the electrons and transfer them (partially) to the ligands. The covalent electron sharing or the ionic charge transfer depends also on the core and valence orbital radii, i.e., on the overlap options.…”

Ba with Unusual Oxidation States in Ba Chalcogenides under Pressure

“…At high pressure, alkali-earth metals experience complex orbital hybridizations (e.g., s-p and s-d) and structural transitions, and part of their valence electrons might even become localized at the interstitials, forming electrides. , Additionally, some of them even become good superconductors under pressure . Among them, barium (Ba), with electron configuration of [Xe]­6s 2 , is the heaviest member stable to radioactive decay, and shows the strongest reactive activity . Under pressure, the reactions of Ba with other main-group elements form unusual stoichiometric compounds (e.g., BaSi 5 , BaGe 3 , , BaF 5 , BaH 6 , and BaH 12 ) with exotic properties, indicating that stable compositions and structures are also strongly related to the characteristics of the other element and synthetic conditions.…”

“…14 Among them, barium (Ba), with electron configuration of [Xe]6s 2 , is the heaviest member stable to radioactive decay, and shows the strongest reactive activity. 15 Under pressure, the reactions of Ba with other main-group elements form unusual stoichiometric compounds (e.g., BaSi 5 , 16 BaGe 3 , 17,18 BaF 5 , 19 BaH 6 , 20 and BaH 12 21 ) with exotic properties, indicating that stable compositions and structures are also strongly related to the characteristics of the other element and synthetic conditions. More interestingly, Ba in pressure-induced fluorides shows the attribute of 5p-elements.…”