Eric Scerri

Since 1969, the international chemistry community has only held conferences on the topic of the Periodic Table three times, and the 2012 conference in Cusco, Peru was the first in almost a decade. The conference was highly interdisciplinary, featuring papers on geology, physics, mathematical and theoretical chemistry, the history and philosophy of chemistry, and chemical education, from the most reputable Periodic Table scholars across the world. Eric Scerri and Guillermo Restrepo have collected fifteen of the strongest papers presented at this conference, from the most notable Periodic Table scholars. The collected volume will contain pieces on chemistry, philosophy of science, applied mathematics, and science education.

The term “element” is typically used in two distinct senses. First it is taken to mean isolated simple substances such as the green gas chlorine or the yellow solid sulphur. In some languages, including English, it is also used to denote an underlying abstract concept that subsumes simple substances but possesses no properties as such. The allotropes and isotopes of carbon, for example, all represent elements in the sense of simple substances. However, the unique position for the element carbon in the periodic table refers to the abstract sense of “element.” The dual definition of elements proposed by the International Union for Pure and Applied Chemistry contrasts an abstract meaning and an operational one. Nevertheless, the philosophical aspects of this notion are not fully captured by the IUPAC definition, despite the fact that they were crucial for the construction of the periodic table. This pivotal chemical notion remains ambiguous and such ambiguity raises problems at the epistemic, logical, and educational levels. These aspects are discussed throughout the book, from different perspectives. This collective book provides an overview of the current state of the debate on the notion of chemical element. Its authors are historians of chemistry, philosophers of chemistry, and chemists with epistemological and educational concerns.

The article begins by asking whether contemporary chemists accept the dual meaning of the term “element” that has been discussed at various stages in the development of chemistry. It proceeds to review the key ideas in the contemporary philosophical debate, including the views of Mendeleev and Paneth and whether a microscopic interpretation of the distinction can be upheld. Regardless of any interpretation, the abstract sense of “element” is then used to resolve the specific question of what elements belong to group 3 of the periodic table. The article concludes with a brief examination of several remaining open questions that need further clarification.

The philosophy of chemistry has emerged in recent years as a new and autonomous field within the Anglo-American philosophical tradition. With the development of this new discipline, Eric Scerri and Grant Fisher's "Essays in the Philosophy of Chemistry" is a timely and definitive guide to all current thought in this field. This edited volume will serve to map out the distinctive features of the field and its connections to the philosophies of the natural sciences and general philosophy of science more broadly. It will be a reference for students and professional alike. Both the philosophy of chemistry and philosophies of scientific practice alike reflect the splitting of analytical and continental scholastic traditions, and some philosophers are turning for inspiration from the familiar resources of analytical philosophy to influences from the continental tradition and pragmatism. While philosophy of chemistry is practiced very much within the familiar analytical tradition, it is also capable of trail-blazing new philosophical approaches. In such a way, the seemingly disparate disciplines such as the "hard sciences" and philosophy become much more linked.

After briefly reviewing the meaning and recent literature on structural realism in general, the authors propose that the periodic system provides an example of structural realism in chemistry, a subject that has received very little attention. The dual meaning of the term element is discussed, as previously described by Mendeleev and Paneth. It is argued that the structure of the periodic system, which concerns the abstract elements, is ‘more real’ than the elements in the sense of simple substances. The challenges that the periodic system has faced since its discovery are reviewed, as are the evolving theoretical explanations for the periodic system, in order to illustrate its resilience. It is also proposed that considering elements as abstract basic substances, as they were called by Paneth, can serve to settle various ongoing debates regarding the placement of certain elements in the periodic table.

The article sets out to clarify a number of confusions that exist in connection with the Born–Oppenheimer approximation (BOA) (Born-Oppenheimer, 1927). It is generally claimed that chemistry cannot be reduced to quantum mechanics because of the nature of this commonly used approximation in quantum chemistry, that is popularly believed to require a ‘clamping’ of the nuclei. It is also claimed that the notion of molecular structure, which is so central to chemistry, cannot be recovered from the quantum mechanical description of molecules and that it must be imposed by hand through the BOA. Such an alleged failure of reduction is then taken to open the door to concepts such as emergence and downward causation. Another mistaken view is that chemists have no choice but to use the BOA whereas there is an entire sub-discipline which involves non-Born Oppenheimer calculations, and which regularly and successfully calculates many chemical and biochemical properties of molecules. Yet another misconception, according to the present author, is the view that the application of the BOA represents a violation of the Heisenberg Uncertainty Principle. Many of the claims made in the philosophy of chemistry community are based on the highly technical papers of authors such as Sutcliffe and Wooley, many of which date from about 50 years ago. While these authors remained skeptical of the possibility of recovering molecular structure from quantum mechanics, others maintained that it would eventually possible to do so. Significant progress has now been made in this direction. For example, whereas it is claimed that the full, or Coulombic Hamiltonian, for a molecule precludes the existence of molecular dipoles, some recent calculations have succeeded in obtaining the exact value of dipole moment of the LiH molecule. Even more significantly, a group in Norway has now succeeded in recovering the structure of the D3 + molecule in a completely ab initio manner without applying the BOA, but through the use of a Monte Carlo approach.

The article contrasts the way that laws are regarded by some philosophers of science with the way that they are regarded by scientists and science educators. After a brief review of the Humean and necessitarian views of scienfic laws, I highlight difference between scientists who regard laws as being merely descriptive and philosophers who generally regard them as being explanatory and, in some cases, as being necessary. I also discuss the views of two prominent philosophers of science who deny any role for scienfic laws. I conclude that science educators should be wary of adopng the necessitarian view of scienfic laws.

In this article I examine several related views expressed by Robin Hendry concerning molecular structure, emergence and chemical bonding. There is a long-standing problem in the philosophy of chemistry arising from the fact that molecular structure cannot be strictly derived from quantum mechanics. Two or more compounds which share a molecular formula, but which differ with respect to their structures, have identical Hamiltonian operators within the quantum mechanical formalism. As a consequence, the properties of all such isomers yield precisely the same calculated quantities such as their energies, dipole moments etc. The only means through which the difference between the isomers can be recovered is to build their structures into the quantum mechanical calculations, something that is carried out by the application of the Born-Oppenheimer approximation. Consequently, it has been argued by many authors that molecular structure is written in ‘by hand’ rather than derived. Robin Hendry is one such author, but he goes a great deal further by proposing that this situation implies the existence of emergence and downward causation. In the current article I argue that there are alternative explanations which render emergence and downward causation redundant. Such an alternative lies in the notion of quantum decoherence and the appeal to work in the foundations of physics, which posits that the various isomers exist as a superposition until their wavefunctions are collapsed either by observation or by interacting with their environment. Hendry also alludes to a debate among chemists as to whether chemical bonds are real or not, in the sense of directional connections between two or more nuclei in any given molecule. I reject this view and propose that the structural and energetic views of chemical bonding, that have been discussed by some philosophers of chemistry including Hendry, do not refer to any essential ontological differences. I agree that chemists view bonding in a more realistic fashion and may consider bonds to be in some senses real, while physicists may consider bonding in more abstract energetic terms. However, I do not believe that such differences in scientific practice and attitudes should be considered to offer a window as to the ontological status of bonding or whether bonding is real. Finally, I discuss the kinetic energy school of chemical bonding which would seem to challenge any notion of bonds as directional entities, since bonding is no longer regarded as being primarily due to the build-up of electron density between nuclei.

This chapter provides a detailed account of how John Nicholson’s atomic theory of the early 20th century was spectacularly successful in accommodating as well as predicting some spectral lines in the solar corona and in the nebula in Orion’s Belt. The theory was soon shown to be completely mistaken in several respects, and yet it served to introduce the notion of the quantization of angular momentum of electrons in any atom. Armed with this key idea, Bohr was able to develop the first successful model of the hydrogen atom and to initiate the quantum theory of atomic physics. This example is used to argue for an evolutionary and “organic” view of the manner in which scientific theories develop and to dispute Kuhn’s notion of scientific revolutions, while agreeing, nevertheless, with the later Kuhn’s insistence on the evolutionary development of scientific concepts and his denial that science approaches a pre-existing and exterior “truth.”

Robin Hendry has presented an account of two equally valid ways of understanding the nature of chemical bonding, consisting of what the terms the structural and the energetic views respectively. In response, Weisberg has issued a “challenge to the structural view”, thus implying that the energetic view is the more correct of the two conceptions. In doing so Weisberg identifies the delocalization of electrons as the one robust feature that underlies the increasingly accurate quantum mechanical calculations starting with the Heitler-London method and moving on to such approaches as the valence bond and molecular orbital theories of chemical bonding. The present article provides a critical evaluation of Weisberg’s article and concludes that he fails to characterize the nature of chemical bonding in several respects. I claim that Hendry’s structural and energetic views remain as equally viable ways of understanding chemical bonding. Whereas the structural view is more appropriate for chemists, the energetic view is preferable to physicists. Neither view is more correct unless one subscribes to the naively reductionist view of considering that the more physical energetic view is the more correct one.

The article begins with a response to a recent contribution by Jensen, in which he has criticized several aspects of the use of triads of elements, including Döbereiner’s original introduction of the concept and the modern use of atomic number triads by some authors including myself. Such triads are groups of three elements, one of which has approximately the average atomic weight of the other two elements, as well as having intermediate chemical reactivity. I also examine Jensen’s attempted reconstruction Mendeleev’s use of triads in predicting the atomic weights of three hitherto unknown elements, that were subsequently named gallium, germanium and scandium. The present article then considers the use of atomic number triads, in conjunction with the phenomenon of first member anomaly, in order to offer support for Janet’s left-step periodic table, in which helium is relocated into group 2 of the table. Such a table features triads in which the 2nd and third elements of each group, without fail, fall into periods of equal length, a feature that is absent in the conventional 18-column or the conventional 32-column table. The dual sense of the term element, which is the source of much discussion in the philosophy of chemistry, is alluded to in further support of such a relocation of helium that may at first appear to contradict chemical intuition.