What is an element? What is the periodic table? And what does quantum mechanics contribute to the question?

Abstract

This article considers two important traditions concerning the chemical elements. The first is the meaning of the term ''element'' including the distinctions between element as basic substance, as simple substance and as combined simple substance. In addition to briefly tracing the historical development of these distinctions, I make comments on the recent attempts to clarify the fundamental notion of element as basic substance for which I believe the term ''element'' is best reserved. This discussion has focused on the writings of Fritz Paneth which are here analyzed from a new perspective. The other tradition concerns the reduction of chemistry to quantum mechanics and an understanding of chemical elements through their microscopic components such as protons, neutrons and electrons. I claim that the use of electronic configurations has still not yet settled the question of the placement of several elements and discuss an alternative criterion based on maximizing triads of elements. I also point out another possible limitation to the reductive approach, namely the failure, up to now, to obtain a derivation of the Madelung rule. Mention is made of some recent similarity studies which could be used to clarify the nature of 'elements'. Although it has been suggested that the notion of element as basic substance should be considered in terms of fundamental particles like protons and electrons, I resist this move and conclude that the quantum mechanical tradition has not had much impact on the question of what is an element which remains an essentially philosophical issue.Let me start with the first question, what is an element? We think we all know what elements are. They are things like hydrogen, oxygen, mercury, gold and uranium from which all compounds and consequently all substances are made. They are the building blocks of the whole universe. Of course all this is true but I want to dig a little deeper. I

Why much of Chemistry may be indisputably non-bonded?

“…The state-of-the-art of the non-covalent interaction world was revisited. Among the eighteen groups of the periodic table (CHAVERRI, 1953;GIUNTA;MAINZ;GIROLAMI, 2021;SCERRI, 2012), it is known that elements of ten of these ones can form intermolecular models, whose definitions were reviewed at the light of the most modern quantum computational approaches. On the basis in the energetic context, the strength of these interactions is broadly varied with distinct contributions of electrostatic, induction, and in some cases, the repulsive exchange energy.…”

The value of vague ideas in the development of the periodic system of chemical elements

“…Exact triads based on atomic numbers are strong proxies for chemical periodicity introduced by chemical similarity and are still being discussed today: there is a triad Y, Lu, Lr that is currently being used as evidence in efforts to decide which elements should be listed in group 3 (Scerri 2015). Scerri (Scerri 2012) correctly dispels the notion that electronic configurations of elements settle the position of elements in the PTE 17 and proposes instead the maximization of triads of elements. The fact that initially only four elemental triads were found by Döbereiner did not prevent further developments by Gmelin, Dumas, and Lenssen, who in 1857 arranged the 58 known elements into 20 triads and explored relationships between triads (Scerri 2007e).…”

“…Quantum mechanics did not and cannot derive the periodic system of elements, nor the concepts of chemical bonding found in molecular and extended structures. The different lengths of the periods in PTE are not derived from ab-initio quantum mechanical calculations (Scerri 2012). Instead in a subfield of chemistry, quantum chemistry, we apply quantum mechanical tools to chemical systems (Schummer 1998), similar to how we approach superconducting materials.…”

Formal structure of periodic system of elements

“…Despite the relevance of similarity and order for the periodic system [22], 2 they are considered as separate aspects of it, with some emphasis on classification [24][25][26][27] 3 caused by the, taken for granted, ordering of the elements based upon atomic number. Whereas the possibilities for classifying are multiple given the huge number of properties chemical elements have, an exceptional example stressing ordering over similarity for the case of the table is the definition from Wikipedia: 'The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configurations, and recurring chemical properties' [29].…”