A historical reconstruction of the concept of isotope and its educational value

This paper offers a historically grounded reconstruction of the emergence of the concept of isotope, highlighting its novelty as a major redefinition of atomic identity rather than a simple empirical addition to atomic theory. It shows that isotopy emerged through the convergence of rare-earth chemistry, radioactivity, and spectroscopy, and was consolidated by Soddy, Thomson, and Bohr. Beyond its historical significance, this case illustrates key aspects of the nature of science, including the role of anomalies, conceptual change, and model-building. Incorporating this development into teaching can promote scientific literacy and a deeper understanding of how scientific knowledge evolves.