Gilbert Lewis and the electronic period of radical chemistry

JUAN CAMILO MARTÍNEZ GONZÁLEZ; KLAUS RUTHENBERG

Leuven

Workshop; 2ND LEUVEN - BUENOS AIRES WORKSHOP ON PHILOSOPHY OF PHYSICS AND CHEMISTRY; 2018

KU Leuven

?Radical?, as a word with a conceptual meaning in chemistry, was introduced by Lavoisier in his Traité in 1789. He used this word for example to describe that water is made of components rather than to be an element. In the following, many influential chemists of the 19th century applied and developed this notion, like, for example Berzelius, Liebig, and Dumas. Berzelius, for instance, gave radicals the meaning of ?element imitators?, and the latter two proposed to consider organic chemistry as the science of ?complex radicals?, and inorganic chemistry as the science of ?simple radicals?.Although their definition has been shifted in modern chemistry, the contents of these early concepts of radicals (and types) are still vivid in chemistry, for example referring to the use of molecular fragments like the ?methyl group? or the ?hydroxyl group? in the talk about reactions and structures. Since the 1920s, radicals are defined as chemical species with at least one unpaired electron in the outer atomic shell (s. Lewis 1923). Hence, for a rough overview the history of chemical radicals might be put into three parts: the speculative, the synthetic, and the electronic period (Ruthenberg 2015). The present contribution will mainly refer to the synthetic period.From very early on the question whether or not radicals could be isolated (or synthesized) to yield manifest stuff portions was fascinating the chemists. However, the first successful ?preparation? of such a ?free radical? was reported by Moses Gomberg (1866 ? 1947) only in 1900. He came up with results which eventually ? that is after many years of critical discussion ? convinced the scientific community that certain free radicals can be assigned substantial existence (Gomberg 1914). About 30 years later Friedrich Paneth (1887 ? 1958) and his co-workers published empirical evidence for the existence of the quite unstable methyl- and ethyl radicals in sophisticated, ingenious experiments (s. Paneth and Hofeditz 1929).The present contribution is an attempt to come to terms with the settlement of the modern radical concept mainly with respect to the latter historical example. Some topics pertinent to the history and philosophy of chemistry shall be investigated in particular. For example, the relation of the substance (or stuff) notion and the radical concept will be analysed (cf. Timmermans 1940, van Brakel 2000), and critical reference will be made to the philosophy of experiment (cf. Hacking 1984, Heidelberger 1998, Chang 2005), and the concept of preparation (which recently has been refreshed in the framework of ?historical epistemology? by Rheinberger 2006). Moreover, the applicability of the actor-model to chemical radicals (and chemical substances in general) will be analysed (Latour 1999).