The Molecule as an Epistemic Object: An Ontosemiotic Perspective on Its Historical Emergence

This article presents an epistemological and historical analysis of the emergence and evolution of the concept of molecule, using the Ontosemiotic Approach to knowledge and instruction as its theoretical framework. From this perspective, the meaning of the term ‘molecule’ is understood not as a fixed definition but pragmatically: as a system of operative and discursive practices directed towards solving specific problems in historically situated contexts. Through a diachronic study, the paper identifies and characterizes a series of partial meanings of the concept, from Dalton’s compound particles and the Avogadro–Cannizzaro distinction between atoms and molecules to the structural representations of organic chemistry and contemporary quantum-mechanical treatments, together with the hybrid configurations that connect the last two. It then examines how these partial meanings are articulated into a holistic meaning of the concept, bringing out the discontinuities, semiotic mediations and shifts in ontological commitments that have shaped its development. The study thus shows how the Ontosemiotic Approach can be used to analyse the plurality of meanings of chemical concepts and their coexistence in practice, and it suggests hypotheses for teaching the concept of molecule that remain to be tested empirically.