Images of orbitals in twentieth-century General Chemistry textbooks: a semiotic analysis

Abstract

This paper aims at investigating how the images of orbitals were presented in undergraduate General Chemistry textbooks throughout the twentieth century. Special attention was given to ontological and epistemological aspects related to such images. Images of orbitals from twenty-six textbooks used in Brazilian universities were analyzed according to Peircean semiotics, in order to assess: the nature of the orbital; what is the relation between representation and the represented object; what aspects of the object are highlighted by means of the representation; what are the limits and potentialities of the representation. It is observed that the images of orbitals in the textbooks are generally described as representations of maximum probability density and identified as limit surfaces. Such images present orbitals as possessing well defined sizes, shapes and directional nature. There is not sufficient information in most textbooks on the meaning of such images, especially regarding: the object of which representation takes place; how the images were produced; what aspects of the object the representation highlight; and what are the similarities and differences between the several images related to an orbital. Teaching difficulties arising from the features discussed here may be overcome by means of explicit discussion on the production, use and meaning of the representations, supported by Peircean semiotics.