The classical model of the molecule assumes that it has a definite shape and structure like a mechanical object in the world of possible experience. This study deals with this assumption so as to shed some light on the foundations of the model. Arguments based on Kant’s theory of transcendental idealism suggest that neither shape nor structure are attributes of the molecule, but are rather contributions of the subject. This claim has great relevance to the questions of whether or not (...) a quantum treatment of the molecule can derive structure without recourse to any approximation, and the possible existence of emergence and downward causation. The answer to the first question is in the negative, and to the second is that agnosticism is the only possible attitude to have toward this problem. We are creatures who can only imagine what is going on by observing phenomena. All that is accessible to us is the modal structure of the model. The causal structure of the real system is not. From the same point of view and taking the concept of the affordance into account, the adequacy of the concept of molecular structure will be argued. The point is to specify what objects the concept can legitimately be applied to. Also briefly discussed in relation to shape and structure is the idea that molecular chirality might be a probe to reveal the nature of space. (shrink)

Perhaps the hottest topic in the philosophy of chemistry is that of the relationship between chemistry and physics. The problem finds one of its main manifestations in the debate about the nature of molecular structure, given by the spatial arrangement of the nuclei in a molecule. The traditional strategy to address the problem is to consider chemical cases that challenge the definition of molecular structure in quantum–mechanical terms. Instead of taking that top-down strategy, in this paper we face the problem (...) of the reduction of molecular structure to quantum mechanics from a bottom-up perspective: our aim is to show how the theoretical peculiarities of quantum mechanics stand against the possibility of molecular structure, defined in terms of the spatial relations of the nuclei conceived as individual localized objects. We will argue that, according to the theory, quantum “particles” are not individuals that can be identified as different from others and that can be reidentified through time; therefore, they do not have the ontological stability necessary to maintain the relations that can lead to a spatially definite system with an identifiable shape. On the other hand, although quantum chemists use the resources supplied by quantum mechanics with successful results, this does no mean reduction: their “approximations” add certain assumptions that are not justified in the context of quantum mechanics or are even inconsistent with the very formal structure of the theory. (shrink)

Although during the last decades the philosophy of chemistry has greatly extended its thematic scope, the main difficulties appear in the attempt to link the chemical description of atoms and molecules and the description supplied by quantum mechanics. The aim of this paper is to analyze how the difficulties that threaten the continuous conceptual link between molecular chemistry and quantum mechanics can be overcome or, at least, moderated from the perspective of BM. With this purpose, in “The quantum-mechanical challenges” section (...) the foundational incompatibility between chemical and SQM descriptions will be briefly recalled. “Bohmian mechanics” section will be devoted to explain the main features of BM. In “Empirical equivalence and underdetermination” section, the consequences of the empirical equivalence between SQM and BM will be discussed. Finally, in the Conclusion, we will stress the scope of the obtained conclusions and the philosophical difficulties that still remain even after adopting BM for foundational purposes. (shrink)

Although during the last decades the philosophy of chemistry has greatly extended its thematic scope, the main difficulties appear in the attempt to link the chemical description of atoms and molecules and the description supplied by quantum mechanics. The aim of this paper is to analyze how the difficulties that threaten the continuous conceptual link between molecular chemistry and quantum mechanics can be overcome or, at least, moderated from the perspective of BM. With this purpose, in “The quantum-mechanical challenges” section (...) the foundational incompatibility between chemical and SQM descriptions will be briefly recalled. “Bohmian mechanics” section will be devoted to explain the main features of BM. In “Empirical equivalence and underdetermination” section, the consequences of the empirical equivalence between SQM and BM will be discussed. Finally, in the Conclusion, we will stress the scope of the obtained conclusions and the philosophical difficulties that still remain even after adopting BM for foundational purposes. (shrink)

Intra-molecular connectivity (that is, chemical structure) does not emerge from computations based on fundamental quantum-mechanical principles. In order to compute molecular electronic energies (of C 3 H 4 hydrocarbons, for instance) quantum chemists must insert intra-molecular connectivity “by hand.” Some take this as an indication that chemistry cannot be reduced to physics: others consider it as evidence that quantum chemistry needs new logical foundations. Such discussions are generally synchronic rather than diachronic —that is, they neglect ‘historical’ aspects. However, systems of (...) interest to chemists generally are metastable . In many cases chemical systems of a given elemental composition may exist in any one of several different metastable states depending on the history of the system. Molecular structure generally depends on contingent historical circumstances of synthesis and separation, rather than solely or mainly on relative energies of alternative stable states, those energies in turn determined by relationships among components. Chemical structure is usually ‘kinetically-determined’ rather than ‘thermodynamically-determined.’ For instance, cyclical hydrocarbon ring-systems (as in cyclopropene) are produced only in special circumstances. Adequate theoretical treatments must take account of the persistent effects of such contingent historical events whenever they are relevant—as they generally are in chemistry. (shrink)

A new chronology is introduced to address the history of chemistry, with educational purposes, particularly for the end of the twentieth century and here identified as the fifth chemical revolution. Each revolution are considered in terms of the Kuhnian notion of ‘exemplar,’ rather than ‘paradigm.’ This approach enables the incorporation of instruments, as well as concepts and the rise of new subdisciplines into the revolutionary process and provides a more adequate representation of such periods of development and consolidation. The fifth (...) revolution developed from 1973 to 1999 and is characterized by a deep transformation in the very heart of chemistry. That is to say, the size and type of objects, the way in which they must be done and the time in which they are transformed. In one way or another, chemistry’ limits had been set out. (shrink)

Science makes extensive use of models, i.e. simplified or idealized representations of the systems found in the physical world. Models fall into at least two categories: mathematical and physical models. In this paper, we focus attention mainly on the latter, trying to show that they are essential tools not only of the scientific description of the world ‘out there’, but of man’s cognition of things, especially things not directly accessible to the senses. The spring-and-ball model of chemistry is a most (...) instructive example of a physical model. In other disciplines, from cosmology to physiology, models are used that are of the same kind or play the same role. It is concluded that physical models are objects which belong to the world accessible to man’s direct experience, often constructed ad hoc and possibly idealized. They serve as referents for analogies, which appear to be indispensable in most aspects of scientific theorizing, especially for the understanding of the submicroscopic levels of reality. (shrink)

Molecular structure (MS) has been treated as a convention or an epiphenomenon by physicists and quantum chemists interpreting the mathematical formalism of quantum mechanics as the essential reality criterion in the submicroscopic world (R2 world). This paper argues that, (a) even in the R2 world there is a class of entities which are real per se, even though they cannot be separated from their material support, and MS may belong to that class; (b) MS actualizes a particular molecule from the (...) many potentialities of a given set of nuclei and electrons, all present in the same Schroedinger equation; (c) MS is a fact established in the XIXth century, albeit as a result of circumstantial evidence (because of its belonging to the R2 world); (d) the fact that MS is known, as all objects of the atomic world, in terms of analogies with macroscopic models, is not valid grounds for questioning its reality; (e) MS is a set of topological as well as geometrical relations. All along the discussion, observability according to Bohr, Heisenberg, Feynman is taken as the essential criterion of reality in the R2 world. On its basis, quantum mechanics is by no means in conflict with the reality of molecular structure and shape. On the other hand, the question of the minimum lifetime required for a MS proper to exist should be left open, pending a detailed analysis of measurement techniques. (shrink)

Molecular structure has been treated as a convention or an epiphenomenon by physicists and quantum chemists interpreting the mathematical formalism of quantum mechanics as the essential reality criterion in the submicroscopic world . This paper argues that, even in the R2 world there is a class of entities which are real per se, even though they cannot be separated from their material support, and MS may belong to that class; MS actualizes a particular molecule from the many potentialities of a (...) given set of nuclei and electrons, all present in the same Schrödinger equation; MS is a fact established in the XIXth century, albeit as a result of circumstantial evidence ; the fact that MS is known, as all objects of the atomic world, in terms of analogies with macroscopic models, is not valid grounds for questioning its reality; MS is a set of topological as well as geometrical relations. All along the discussion, observability according to Bohr, Heisenberg, Feynman is taken as the essential criterion of reality in the R2 world. On its basis, quantum mechanics is by no means in conflict with the reality of molecular structure and shape. On the other hand, the question of the minimum lifetime required for a MS proper to exist should be left open, pending a detailed analysis of measurement techniques. (shrink)

For many decades, chemists regarded rigid models of molecular structure as representing structures of real molecules as their attributes. However, new experimental data required a new theoretical conceptualization. The rigid model has been replaced with a dynamic model in which molecular structure is changed under the influence of environmental conditions. The above case shows some problems connected with recognizing theoretical models as structural representations of real empirical systems. Owing to the fact that theoretical models of molecular structure obtain local interpretations (...) with a procedural character, they can be carriers of specific information about structures of real molecules. Finally, I argue that, although theoretical models can be well corroborated empirically, they cannot be treated as representations of real empirical systems but can play a very important role in experimental practice. (shrink)