Elena GHibaudi

In the present work, the notion of chemical element is analyzed from the perspective of chemical education. Chemists refer to elements either as the final term of chemical analysis (i.e., simple substances) or as what persists in a chemical change. This duality has deep historical roots and it is sanctioned by IUPAC’s definition of chemical element. Nevertheless, it is inherently contradictory and it may result in deep misunderstandings in the educational context. After discussing the problems raised by the identification of the element with any material body—either macroscopic or microscopic—we analyze a number of definitions of elements, proposed by chemists, epistemologists, and educators. After pointing out the strengths and weaknesses of such definitions, we argue that the chemical element is a unifying chemical concept that designates an abstract category, identified by the atomic number.

In recent years, the definition of mole, the unit of the amount of substance, has changed to have the base units of the International System defined by “explicit-constant” formulations. The old definition, by referring explicitly to both mass and elementary units, suggests that the mole is a bridge between the macroscopic and microscopic registers. Conversely, the new definition emphasizes the aspect of counting, referred to any kind of elementary unit. Paradoxically, this results in the disappearance of the notion of substance from the very unit of the quantity amount of substance. This change of definition elicited both positive and negative remarks from various authors, in relation to its epistemological, disciplinary, lexical and educational implications. In the present paper, we analyze some of these issues, highlighting the (conflicting) motivations of metrologists and chemists. We argue that the new definition of mole reflects a view of chemistry according to which the microscopic perspective prevails, possibly entailing the loss of reference to the macroscopic register; this could be related with the profound change undergone by the cognitive practices of chemistry along this last century.

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 concepts of molecular structure and molecular shape are ubiquitous in the chemical literature, where they are often taken as synonyms, with unavoidable drawbacks in chemistry teaching. A third concept, molecular topology, is less frequent but it is a reference term in molecular research domains such as Quantitative Structure–Activity Relationships. The present paper proposes an epistemological analysis of these three notions, aimed at clarifying the nature of their relationship, as well as the contiguities and differences between them. At first, we discuss the various acceptations of the terms molecular structure and molecular shape. Then, we examine some crucial milestones in the history of these concepts and we analyse the relationship between structure, shape and topology from an epistemological viewpoint. We point out the distinguishing features of each concept and we show that their semantic openness, that may be fruitful in a specialized context, turns into a source of incoherence and inaccuracy in the teaching context, fostered by the misleading use of these terms made by textbooks. Eventually, we propose a criterion fit to discriminate between the conceptual domains of molecular shape, molecular structure and molecular topology.

A chemical substance is instantiated in the material world by a number of quantities of such substance, placed in different locations. A change of location implies a change in the net of relationships entertained by the QCS with the region wherein it is found. This fact entails changes of the ontological status of the CS, as this is not fully determined by the inherent features of the CS and includes a relevant relational contribution. In order to demonstrate this thesis, we have chosen to analyse the status of quantities of a same CS that are synchronically located in different spacetime regions: a synthetic lab, a lab where the QCS is turned into a material, an industrial plant, the market where the QCS gets a price and a dump waste where the QCS is discarded, respectively: Chemical substance Open image in new window material Open image in new window product Open image in new window goods Open image in new window wasteThe use of first-order predicate logic, mereology and locative logic allows carrying out a regimentation process that highlights the ontological commitments implied by the formal expressions through which each element of the aforementioned series can be described. The presence of relational properties discloses the systemic nature of the CS instantiated within a spacetime region. The implications of such an aspect are discussed.

The present work is a comment of a recent paper by Fortin and coauthors in which the authors propose the introduction of Bohmian mechanics in the philosophy of chemistry and the use of standard quantum mechanics as a mere instrument of prediction. This way would allow overcoming the obstacles found in linking molecular chemistry and quantum mechanics. Starting from some remarks on the orbital concept, we highlight and discuss some general issues that need to be taken into account when two scientific theories coexist within the same investigation field, i.e. SQM and BM.