Rol De Las Triadas

Found Chem (2010) 12:69–83 DOI 10.1007/s10698-010-9082-9

Explaining the periodic table, and the role of chemical triads
Eric Scerri

Published online: 28 January 2010 Ó Springer Science+Business Media B.V. 2010

Abstract Some recent work in mathematical chemistry is discussed. It is claimed that quantum mechanics does not provide a conclusive means of classifying certain elements likehydrogen and helium into their appropriate groups. An alternative approach using atomic number triads is proposed and the validity of this approach is defended in the light of some predictions made via an information theoretic approach that suggests a connection between nuclear structure and electronic structure of atoms. Keywords Chemistry Á Quantum mechanics Á Periodic table Á Information theory ÁChemical triads

Introduction Much work in the philosophy of chemistry has focused on the question of reduction (Bogaard 1978; Hendry 2008; Ramsey 2006; Scerri 1994). These authors consider the reduction of chemistry to quantum mechanics and seldom mention a broader sense of ‘reduction’ to numerical regularities in the absence of a physical theory. In chemistry the discovery of numericalregularities among groups of three elements such as lithium, ¨ sodium and potassium produced the concept of triads as first discussed by Dobereiner (1829). Many triads were then assembled together to produce some early periodic systems by Lothar Meyer and Mendeleev among others. At this point there was no explanatory theory to account for the existence of chemical periodicity. Such a theory becameavailable some time later, namely in the 1920s with the advent of quantum mechanics and the notion of electrons occupying shells around the nucleus of the atoms of the various elements. I suggest that the use of a triad approach may be considered as a form of reduction, broadly construed, although I will postpone arguing the case for a later paper.

E. Scerri (&) Department of Chemistry & Biochemistry,UCLA, Charles Young Drive East, Los Angeles, CA 90095, USA e-mail: scerri@chem.ucla.edu

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Turning to current developments, the field of mathematical chemistry has existed for several decades and yet it is never mentioned in the context of the reduction of chemistry.1 This is an unfortunate omission in my view. In a later section of the present paper a mathematicalapproach to the periodic table, due to Bonchev, will be discussed.

Reduction of the periodic table in particular Attempts to explain the periodic table have included reduction to quantum mechanics as well as approaches from mathematical chemistry. The latter work has been approached through various group theoretical schemes (Novaro 1973; Kibler 1989, 2007; Ostrovsky ´ 2005), similarity studies(Carbo-Dorca 1998, 2000; Restrepo and Pachon 2007; Sneath 2000), and other mathematical approaches (Scerri et al. 1998).2 The periodic table is an absolutely central concept in the study of chemistry and defies simple categorization, while at the same time being the supreme example of a scientific system of classification. In addition to being described as a system of classification the periodic table hasbeen described as a model, a theory, a representation and many things besides (Shapere 1974; Weisberg 2007). It is important theoretically as well as being of immense educational and practical value to working scientists. A seldom mentioned attribute of the periodic table is that it concerns a rather holistic and all-inclusive aspect of chemistry since it embodies all the elements and in additionhighlights layer upon layer of relationships among the elements. I would like to suggest that quantum mechanics provides a good means of reducing the properties of individual elements but is not quite so effective when it comes to capturing some of the more global aspects of the periodic table. By global property I intend, for example, the membership of elements to particular groups in the...