Seifert, V. (2019)

The role of idealisations in describing an isolated molecule

In this paper, I argue that there is an idealisation made in chemistry and in quantum mechanics which has not been identified as such. Specifically, when chemistry and quantum mechanics each describe an isolated molecule they each assume that the molecule is stable and has structure. This is an idealisation because (i) stability and structure are partially determined by factors that concern the context in which a molecule is considered (namely thermodynamic conditions, time-range of experiment, environment, etc.); and, (ii) the stability and structure of a molecule can only be empirically identified with reference to those factors. Identifying this assumption as an idealisation can be particularly useful to the investigation of the relation between chemistry and quantum mechanics, as existing philosophical positions on this issue focus on how successfully (or not) the two theories describe the structure of stable isolated molecules. Moreover, this idealisation can inform one’s understanding of the nature of stability and structure, as well as of the function of idealisations in chemistry and in quantum mechanics. The structure of the paper is as follows. First, I briefly present how idealisations are broadly construed and examined in philosophy and I outline the main philosophical questions that have been investigated with respect to idealisations. I then present how stability and structure are described and empirically identified in chemistry and in quantum mechanics. Based on this analysis, I argue that assuming an isolated molecule as being stable and having structure is an idealisation. Lastly, I investigate how this particular idealisation can inform our understanding of different philosophical issues, including the question of the nature of chemical properties as well as the relation between chemistry and quantum mechanics. 


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Foundations of Chemistry

Foundations of Chemistry is an international journal is an interdisciplinary forum in which chemists, biochemists, philosophers, historians, educators and sociologists discuss conceptual and fundamental issues which relate to the `central science' of chemistry  Coverage includes the autonomous role of chemistry between physics and biology and the question of the reduction of chemistry to quantum mechanics.