From Substances to Atoms: Electronegativity Reconsidered

JUAN CAMILO MARTÍNEZ GONZÁLEZ; KLAUS RUTHENBERG

Chicago

Congreso; Philosophy of Science Association Biennal Meeting 2014; 2014

PHILOSOPHY OF SCIENCE ASSOCIATION

The concept of electronegativity is one of the most relevant concepts in chemistry, since used to explain many aspects of reactivity. This concept has a long existence in the knowledge of chemists but it was only defined qualitatively with the advent of the theories of bonding as ?the power of an atom in a molecule to attract electrons to itself? (Pauling 1932). However, the concept of electronegativity itself is far from being precisely determined, and this problem is mainly due to the fact that electronegativity cannot be measured by direct means, and must be inferred on the basis of other properties that can be directly measured. There are two main methods of computing electronegativity: (i) a spectroscopic method, based on the ionization potential I of the isolated atom, and (ii) a thermodynamic method, which uses the enthalpy ΔH° of formation of the molecule. Although usually presented as two ways of measuring a single property, these two methods lead to different concepts. According to the spectroscopic method, electronegativity is an intrinsic property of the atoms. The thermodynamic method considers the atoms in the context of the molecules and, as a consequence, electronegativity is conceived as a relational property. The purpose of the present work is to discuss the problem of the concept of electronegativity from two opposite philosophical perspectives. In the first place, according to a strong reductionist position, the incompatibility between the two views of electronegativity, the intrinsic and the relational views, is only apparent, and will be solved by finding the unification in the quantum realm. But this reductionist hope has to face two difficulties. The first one is that the thermodynamical description of electronegativity trough ΔH° is independent of the quantum-mechanical domain. Second, the difficulties inherent to quantum-chemistry itself, with the coexistence of several models and methods to approach bonding (EV, OM, DFT, QTAiM): the ways in which the measurable property (I) is related with electronegativity is different in the contexts of the different quantum-chemical models of bonding. On the other hand, according to the scientific perspectivism of Giere (2006), scientific descriptions are all perspectival, that is, dependent on the context, the agent and the purpose: scientific representations are four-place relation of the form: ?S uses X to represent W for purposes P?. The difficulty with this proposal is that it presupposes the existence of a single item W to be represented form different perspectives. In the case of electronegativity, on the contrary, we do not know yet if there is a single property in the ontological domain or if ?electronegativity? is a word that subsumes different properties correlated to each other.