Do we know the chemical bond? A case for the ethical teaching of undefined paradigms

Abstract The chemical bond is the biggest paradigm in chemistry. But at the same time it is notoriously complex to define it. Under the assumption that knowing what we do not know makes better students and lecturers, we succinctly describe three approaches to define the bond (energetic, structural, and orbital), their advantages and especially their failures. We propose that these definitions, including their theoretical, practical and even philosophical issues, should be taught to advanced undergraduate chemistry students as an essential introduction to the chemical bond module of quantum chemistry courses. This is a controversial topic due to the lack of consensus in the chemical bond community over this heavily disputed topic and the conflicting pedagogical approach; however, and maybe because of this controversy, the teaching of the definitions of the chemical bond including their open questions and challenges can be positively instructive. Moreover, we propose that teaching the uncertainties of chemistry, especially in relation to the paradigmatic chemical bond, is an ethical matter.