Chemical translators: Pauling, Wheland and their strategies for teaching the theory of resonance

It was well said by Clerk Maxwell: ‘For the sake of persons of different types of mind scientific truth should be presented in different forms, and should be regarded as equally scientific whether it appears in the robust form and colouring of a physical illustration, or in the tenuity and paleness of a symbolical expression.’From N. V. Sidgwick's Presidential Address to the Chemical Society, London, 1937During the years between 1930 and 1950, chemistry underwent a transformation that affected both research and education. New subdisciplines like chemical physics and physical organic chemistry emerged, encouraging an influx of ideas and experimental techniques from physics. X-ray crystallography and other spectroscopic methods became indispensable for determining structures of atoms, molecules and crystals; such chemical concepts as valence and bond were refined within a new explanatory framework based on principles of physics; and the study of reaction mechanisms and rates became closely intertwined with that of structures and properties of chemical compounds. In conjunction with these changes, introductory chemical textbooks began to shift their emphasis from thermodynamic equations and solution theories to three-dimensional arrangements of atoms in molecules and types of chemical bonds. There is no doubt that the most important impetus behind this transformation was the development of quantum mechanics in the mid-1920s, and the most prominent among those who applied it to chemistry was Linus Pauling. And in Pauling's view, ‘the principal contribution of quantum mechanics to chemistry’ was the concept of resonance.The entry of resonance into chemistry, or the reception of the theory of resonance in the chemical community, has drawn considerable attention from historians of science. In particular, they have noted Pauling's flamboyant yet effective style of exposition, which became a factor in the early popularity of the resonance theory in comparison to the molecular orbital theory, another way of applying quantum mechanics to chemical problems. To be sure, the non-mathematical presentation of the resonance theory by Pauling and his collaborator, George Wheland, helped to facilitate the reception; but this presentation was vulnerable to the confusion that arose among chemists owing to the similarity between resonance and tautomerism, or between foreign and indigenous concepts. The reception occurred at the expense of serious misunderstandings about resonance. This paper investigates the ways in which Pauling and Wheland taught, and taught about, the theory of resonance, especially their ways of coping with the difficulties of translating a quantum-mechanical concept into chemical language. Their different strategies for teaching resonance theory deserve a thorough examination, not only because the strategies had to do with their solutions of the philosophical question whether resonance is a real phenomenon or not, and whether the theory of resonance is a chemical theory or a mathematical method of approximation, but also because this examination will illuminate the role of chemical translators in the transmission of knowledge across disciplinary boundaries.