Some recent work in mathematical chemistry is discussed. It is claimed that quantum mechanics does not provide a conclusive means of classifying certain elements like hydrogen 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.

The placement of hydrogen in the periodic table has unique implications for fundamental questions of chemical behavior. Recent arguments in favor of placing hydrogen either separately at the top of the table or as a member of the carbon family are shown to have serious defects. A Coulombic model, in which all compounds of hydrogen are treated as hydrides, places hydrogen exclusively as the first member of the halogen family and forms the basis for reconsideration of fundamental concepts in bonding (...) and structures. The model provides excellent descriptive and predictive ability for structures and reactivities of a wide range of substances. (shrink)

Electronegativity is a quantified, typical chemical concept, which correlates the ability of chemical species to attract electrons during their contact with other species with measurable quantities such as dissociation energies, dipole moments, ionic radii, ionization potentials, electron affinities and spectroscopic data. It is applied to the description and explanation of chemical polarity, reaction mechanisms, other concepts such as acidity and oxidation, the estimation of types of chemical compounds and periodicity. Although this concept is very successful and widely used, and in (...) spite of the fact that it is still subject to scientific investigations, neither a more than intuitive definition nor a generally accepted, logically clear and standardized quantification model has been developed. In the present work, electronegativity is presented and discussed with respect to its main conceptual and operational continuities and discontinuities. We try to analyze the epistemological status of electronegativity, conceived as a typical notion of chemical sciences. Under ‘epistemological status’ we subsume the issues of its reference, its historical persistence, and the relationship between its measurement and quantification. (shrink)

Diagonal relationships in the periodic table were recognized by both Mendeléev and Newlands. More appropriately called isodiagonal relationships, the same three examples of lithium with magnesium, beryllium with aluminum, and boron with silicon, are commonly cited. Here, these three pairs of elements are discussed in detail, together with evidence of isodiagonal linkages elsewhere in the periodic table. General criteria for defining isodiagonality are proposed.

Electronegativity, described by Linus Pauling described as “The power of an atom in a molecule to attract electrons to itself” (Pauling in The nature of the chemical bond, 3rd edn, Cornell University Press, Ithaca, p 88, 1960), is used to predict bond polarity. There are dozens of methods for empirically quantifying electronegativity including: the original thermochemical technique (Pauling in J Am Chem Soc 54:3570–3582, 1932), numerical averaging of the ionisation potential and electron affinity (Mulliken in J Chem Phys 2:782–784, 1934), (...) effective nuclear charge and covalent radius analysis (Sanderson in J Chem Phys 23:2467, 1955) and the averaged successive ionisation energies of an element’s valence electrons (Martynov and Batsanov in Zhurnal Neorganicheskoi Khimii 5:3171–3175, 1980), etc. Indeed, there are such strong correlations between numerous atomic parameters—physical and chemical—that the term “electronegativity” integrates them into a single dimensionless number between 0.78 and 4.00 that can be used to predict/describe/model much of an element’s physical character and chemical behaviour. The design of the common and popular medium form of the periodic table is in large part determined by four quantum numbers and four associated rules. However, adding electronegativity completes the construction so that it displays the multi-parameter periodic law operating in two dimensions, down the groups and across the periods, with minimal ambiguity. (shrink)

This article updates the author’s 1982 argument that lutetium and lawrencium, rather than lanthanum and actinium, should be assigned to the d-block as the heavier analogs of scandium and yttrium, whereas lanthanum and actinium should be considered as the first members of the f-block with irregular configurations. This update is embedded within a detailed analysis of Lavelle’s abortive 2008 attempt to discredit this suggestion.

A modification of the regular medium-form periodic table is presented in which certain elements are placed in more than one position. H is included at the top of both the alkali metals and the halogens; He is above Be and above Ne. The column of noble gases is duplicated as Groups O and 18. The elements of the second and third periods are duplicated above the transition metals. This arrangement displays more patterns and connections between the elements than are seen (...) in the regular format. It fits more facts and so gives better guidance to useful predictions. (shrink)