A rational reconstruction of the origin of the covalent bond and its implications for general chemistry textbooks

The main objectives of this study are: (i) development of a perspective based on history and philosophy of science considerations (rational reconstruction) in order to understand the postulation of the covalent bond by Lewis; (ii) formulation of four criteria based on the perspective; and (iii) evaluation of 27 textbooks based on the four criteria. Results obtained show that most textbooks lacked a history and philosophy of science perspective and did not deal adequately with the following aspects: (i) Lewis's postulation of the covalent bond in 1916 posed considerable conceptual difficulties; (ii) Lewis used the cubical atom (a hypothetical entity) in order to understand the sharing of electrons in the covalent bond (octet rule); (iii) sharing of electrons had to compete with the transfer of electrons (ionic bond) considered to be the dominant paradigm until about 1920; (iv) postulation of the covalent bond (octet rule) was not an inductive generalization based on stability of the noble gases and the high dissociation energy of the covalent bonds; and (v) Pauli exclusion principle provides a theoretical explanation of the sharing of electrons, just as the cubical atom did previously. It is concluded that the development of the covalent bond does not follow the inductivist process, viz. experimental observations lead to scientific laws which later facilitate the elaboration of explanatory theories.