Philosophy of Chemistry

Dov M. Gabbay,Paul Thagard,John Woods

• Publisher: North Holland
• Year: 2011
• ISBN:
  9780080930763
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

Philosophy of Chemistry investigates the foundational concepts and methods of chemistry, the science of the nature of substances and their transformations. This groundbreaking collection, the most thorough treatment of the philosophy of chemistry ever published, brings together philosophers, scientists and historians to map out the central topics in the field. The 33 articles address the history of the philosophy of chemistry and the philosophical importance of some central figures in the history of chemistry; the nature of chemical substances; central chemical concepts and methods, including the chemical bond, the periodic table and reaction mechanisms; and chemistry's relationship to other disciplines such as physics, molecular biology, pharmacy and chemical engineering. This volume serves as a detailed introduction for those new to the field as well as a rich source of new insights and potential research agendas for those already engaged with the philosophy of chemistry.

• Provides a bridge between philosophy and current scientific findings
• Encourages multi-disciplinary dialogue
• Covers theory and applications

Introduction

Robin Findlay Hendry, Paul Needham and Andrea I. Woody

1. What is the Philosophy of Chemistry?

Chemistry is a scientific discipline with a particular subject matter and history of development, and these have endowed the science with a characteristic range of concepts, theories, and methods. Philosophy of chemistry is the systematic critical study of these concepts, theories, and methods, and of the inter-relations between them. This involves reflection on the ways in which they are related to, and potentially distinct from, the concepts, theories, and methods of other sciences.

Since the late eighteenth century, chemists have investigated the composition of chemical substances in terms of a growing list of elements, which constitute the building blocks of chemical composition. Yet elemental constitution is insufficient for composition, because isomers like ethanol (CH₃CH₂OH) and dimethyl ether (CH₃OCH₃) are distinct compounds that contain the same elements in the same proportions. The distinction between isomers demands a notion of chemical structure, and with the notion of structure comes the concept of the chemical bond. The chemical bond has been a central explanatory concept in chemistry for the last century. Bonds are invoked to account for the properties of substances, and the breaking and forming of bonds serve as the framework for making sense of transformation between substances. Yet serious questions remain for any satisfying metaphysics of the chemical bond. Although they are central explanatory devices within chemistry, chemical bonds are themselves explained by appeal to physical theory. Ionic bonding turns to theories of electric charge and covalent bonding turns to non-relativistic quantum mechanics. But as the essays in this volume will attest, the relationships between chemical theory and physical theory are complicated and certainly do not provide the neat reductive relation that has often been presupposed by philosophers and even many scientists. For example, it has been argued that according to quantum mechanics a molecule is not the sort of thing that has a determinate shape, let alone isolated chemical bonds. Philosophy of chemistry aims to provide robust analyses of chemical concepts and to characterize accurately the theoretical relations between chemistry and other sciences, and as a result, to challenge and refine philosophical accounts of, among others, theory reduction, emergent properties, and pluralism.

Philosophy of chemistry also includes investigations into the diverse methods of chemistry, especially those that derive from laboratory practice. The sophisticated methods of analytic chemistry, already evident in the precise techniques and specialized equipment of Lavoisier, have been joined in the twentieth century by powerful resources of spectroscopic instrumentation. Such reliance on sophisticated instrumentation raises a host of philosophical questions concerning the relations between data and theory in chemistry, and attendant issues concerning the role of observation and empiricism more generally. At the same time, the synthetic goals of chemistry, intertwined as they are with industrialization and Western capitalism, yield new methodological questions as chemists develop rational methods for producing new substances with specified properties, and explore automated search procedures to identify viable reaction pathways for chemical synthesis. Philosophy of chemistry encompasses all such issues. This volume presents significant work to date, but much more remains to be done.

2. History of the Philosophy of Chemistry

Philosophy of chemistry is a relatively new subdiscipline within contemporary philosophy of science. It lacks the long history and depth that characterizes twentieth-century philosophy of physics, and falls short of the energetic development of philosophy of biology during the past few decades. Yet throughout the history of philosophy, chemical concepts and theories have appeared in the work of philosophers, both as examples and as topics of discussion in their own right, and scientists themselves have often engaged with theoretical, conceptual and methodological issues that fall within what we would now recognize as philosophy of chemistry. Consider for instance Aristotle's discussion of mixtures and mixing, Frege's metaphorical use of the notion of unsaturatedness in explanation of his distinction between concept and object, or the late 19th-century debates about the status of atomism. In contemporary philosophy there are the extended discussions of ‘water’ stemming from Putnam's twin earth thought experiment, and Kripke's claim that it is necessary that gold has the atomic number 79. These traditions constitute the history of the philosophy of chemistry, and we have sought to provide glimpses of this history in Section 2 of this volume.

Chapter 2.1, Jaap van Brakel's “Prehistory of the Philosophy of Chemistry,” offers a summary of the history of philosophy of chemistry since Kant, alongside a critical examination of why chemistry has been relegated to the sidelines so frequently in recent philosophy of science. This history offers a unique vantage point from which to consider the interests and assumptions, often implicit, that underlie 20th-century philosophy's view of what science is or perhaps should be. These include the inheritance of logical positivism and empiricism, with its particular focus on theories expressed in the language of mathematics and understood as axiomatic systems, and the widespread acceptance of reductionist views of theoretical explanation. Against this background, much of chemistry disappears. Being perhaps too grounded in laboratory and experimental practice, and often practical in its aims and correspondingly pragmatic in its methods, chemical science seldom resembles an orderly top-down enterprise from fundamental theoretical principles. Many of its central ‘theories,’ like molecular structure, are expressed in systems of visual representation rather than mathematical equations. Worse yet, once chemistry is ‘freed’ from such ‘defects,’ what remains can seem to the untutored eye like little more than borrowed physics. Recent work in philosophy of chemistry, as evidenced throughout this volume, brings into sharp relief the shortcomings of such a perspective. Understanding why these discussions are so recent is itself significant.

The remainder of Section 2, Chapters 2.2 to 2.15, is devoted to brief discussions of historical individuals, both chemists and philosophers, whose work is relevant for contemporary philosophy of chemistry. We could not hope for completeness: while we think that the significance of each individual included here cannot be denied, there are undoubtedly others whose contributions also merit serious attention by philosophers. This format is distinct among volumes in the Handbook series and is thus perhaps worthy of comment. As with all volumes in the Handbook series, one goal of this book is to encompass, in some appropriate manner, the significant projects within philosophy of chemistry. Given the relative scarcity of contemporary work, this goal could not be met in any reasonable way without covering the work of historical individuals, many who are scientists, some who are philosophers, and some who are clearly both. Another intended function for this volume is to encourage and support increased research within philosophy of chemistry. We hope that the historical resources in this volume are useful also in this way. Among these brief essays one can find conceptual articulations, methodological principles, and theoretical perspectives that contemporary philosophers might fruitfully mine for future work. A final reason for including the historical section is a shared belief that history of science is of central relevance to the philosophy of science, a belief based on the contemporary commitment to explore science not just in theory, or in the abstract, but also in practice and in detail. Doing so requires philosophers to be closely connected to the history and ongoing developments of particular sciences and to explore the philosophical implications of the modern multiplicity of scientific disciplines.

There is a corresponding caveat: our restriction to discussions of individuals somewhat obscures the deeply social nature of modern science. This restriction was a pragmatic one, based on practical constraints and our knowledge that (i) issues concerning the social nature of science would arise within several of the main philosophical essays in this volume, (ii) the discussions of historical individuals often mention the social contexts in which they were embedded, and (iii) social epistemology remains relatively underdeveloped within contemporary philosophy of science, making it unclear how best to offer historical resources for contemporary philosophical investigation along these lines. Nevertheless, much can be gained from research in the history of science that explores the development of cohesive research traditions, the formation and splintering of scientific disciplines, and the embedding of science in wider social and political contexts. Within chemistry, a plethora of philosophically relevant developments comes to mind: of atomism and energeticism in the nineteenth century, the interactions between chemistry and physics in the first half of the twentieth century, and the emergence of distinct subfields including organic chemistry, material science, and nanotechnology. (See, for example, [[Rocke, 1984], [Nye, 1993], [Servos, 1990] and [Baird et al, 2004]].)

3. Chemical Substances

Chemical substances are the central kinds of chemistry and are as important to understanding chemistry as the species concept—or concepts—is to understanding the biological sciences. There are three long-standing questions about substances: (i) What makes something a sample of the chemical substance that it is? (ii) What kinds of change can an exemplification of that substance survive? (iii) What is the difference between pure compound substances and mixtures? Indeed can such a distinction be drawn at either the microscopic or the macroscopic level?

Turning to the first question, philosophers of language who allude to this issue have taken the work of Kripke and Putnam in the 1970s as their starting point. An outline of their basic moves is given in §4 of Chapter 3.3, Paul Needham's “Modality, Mereology and Substance,” which also provides an introduction to the elements of modal logic and mereology and discusses how they bear on these issues. Kripke and Putnam suggested that the identity of a substance is determined by its microstructure. Applied to the elements, this seems unproblematic. As Robin Hendry argues in Chapter 3.4, “Elements”, the nuclear charge of the constituent atoms is both impervious to chemical change, and also determines (to a large extent) the chemical behaviour of elements and their compounds. Hence it is natural, though not without difficulty, to see nuclear charge as determining the identities of the elements. Compound substances are less tractable. Kripke and Putnam were understandably vague about what they meant by claiming that microstructure (or ‘chemical structure’) determines the identity of a compound substance. Elemental composition is insufficient, because different substances (isomers) may share elemental composition. Elemental composition also fails to distinguish hydrogen chloride (HCl) gas from a mixture of hydrogen and chlorine gases in the corresponding proportions. Moreover, if a compound substance is required to be homogeneous at the molecular level, then pure liquid water will fail the test. Pure liquid water consists of complex congeries of different species like H₃O⁺, OH⁻ and hydrogen-bonded oligomolecular structures, rather than collections of H₂O molecules, and this molecular heterogeneity is responsible for its characteristic properties. This suggests that an adequate account of the relationship between molecular species and chemical substances might require a relation of chemical composition which is consistent with the disappearance of some of the ‘constituent’ molecules in the formation of a sample of the substance. But if the relationship between molecules and substances is this complex, the notion of ‘substance’ may need to be understood independently of molecular constitution.

Simple macroscopic criteria can accomplish some of this work. For example, a compound and a mixture of the constitutive elements in the same mole (mass) proportions will exhibit radically different behaviour under the same conditions of temperature and pressure. At room temperature and pressure, water is liquid but the mixture of hydrogen and oxygen is gas, and under conditions when both are gaseous, the compound is two-thirds the volume of the same mass of the mixture. Thermodynamics, which systematises such features, divides the mass of a system to which it applies into amounts of distinct substances and suggests more theoretically grounded criteria based on Gibbs' phase rule (discussed in several chapters: 3.2. “Substance: The Ontology of Chemistry”, 3.3 “Modality, Mereology and Substance”, 3.5 “Compounds and Mixtures” and 5.4 “Thermodynamics in Chemistry”) or the entropy of mixing. But these call for some interpretation, and do not always draw distinctions that coincide with the boundaries between substances as classically conceived in chemistry. For instance, thermodynamics would seem to view the different isotopes of oxygen (¹⁶O, ¹⁷O and ¹⁸O) as different substances, because mixing pure samples of the different isotopes gives rise to measurable entropy changes. However, as Hendry argues in Chapter 3.4, “Elements”, chemical properties (i.e. dispositions to undergo chemical change) are determined overwhelmingly by nuclear charge, which the different isotopes share, rather than atomic mass, with respect to which they differ.

Mixed substances pose a related set of problems concerning the persistence conditions of substance identity, as Jaap van Brakel discusses in Chapter 3.2, “Substances”. When common salt (NaCl) dissolves in water, the ionic lattice breaks down, and the sodium and chloride ions form complexes with H₂O molecules. Is salt present in brine? If not, what essential property of salt has been lost? If it is the lattice structure that is essential, then molten sodium chloride is no longer salt. On the other hand, if salt is said to be present, what should we say when salt dissolves in a solution already containing sodium hydroxide and potassium chloride? That solution already contains sodium and chloride ions, qualitatively identical to the new arrivals. Hence if the newly added salt survives the dissolution, causal history, as well as microstructure, must be playing a part in substance identity. This would conflict with the plausible view that constitution, rather than causal history, is what determines chemical identity. Two responses offer themselves. One might deny that there is a fact of the matter which sodium and chloride ions belong to which substances...