Abstract
This paper investigates a well-known case of simultaneous discovery in
twentieth-century chemistry, the origins of the concept of hybridisation, in the
light of Kuhn's insights. There has been no ambiguity as to who discovered this
concept, when it was "rst in print, and how important it was. The full-#edged
form of the concept was published in 1931 independently by two American
scientists John C. Slater (1900}1976) and Linus Pauling (1901}1994), although
both of them had made their ideas public earlier: Slater at the American Physical
Society meetings in 1930, and Pauling in the Proceedings of the National
Academy of Sciences in 1928. Slater and Pauling both argued for the necessity of
using an s orbital as well as three p orbitals in the carbon atom in order to
explain carbon's four valences and the tetrahedral structure of methane. The
metaphor &hybridisation' for denoting this mix of s and p orbitals was "rst used
by Robert S. Mulliken and J. H. Van Vleck before gaining currency with the
scienti"c community around 1935.2 The concept of hybridisation was indeed
indispensable for extending the quantum-mechanical interpretation of the
chemical bond as an electron pairing from diatomic molecules to polyatomic
ones.
To be sure, the emergence of hybridisation attests to scientists' growing
interest in exploring the borderland between physics and chemistry, a trend that
led to the creation of physical chemistry in the late nineteenth century and of
chemical physics and quantum chemistry in the 1920s and 30s. Slater and
Pauling themselves experienced and on many occasions talked about the fruitfulness
of interdisciplinary research; and historians have legitimately illuminated
their works by examining them in this broad context.3 Yet the careful analysis of
their research notes and published papers reveals that Slater and Pauling were
working in quite disparate disciplinary traditions, with di!erent approaches, for
di!erent audiences, and towards di!erent goals. The aim of this paper is to
explore their di!erent routes to a common destination*hybridisation*and
thereby to explicate tensions existing between physics and chemistry amidst the
institutional and conceptual overlapping of the two disciplines.