Lewis's Covalent Bond: From Transfer of Electrons to Sharing of Electrons

Lewis (1916) is generally considered to have presented the first satisfactory model of the covalent (shared pair) bond based on the cubic atom in 1916. It is important to note that the genesis of the cubic atom can be traced to an unpublished memorandum written by Lewis in 1902 and recounted by him in the following terms:

In the year 1902 (while I was attempting to explain to an elementary class in chemistry some of the ideas involved in the periodic law) becoming interested in the new theory of the electron (Thomson's discovery of the electron in 1897), and combining this idea with those which are implied in the periodic classification, I formed an idea of the inner structure of the atom (model of the cubic atom) which, although it contained crudities, I have ever since regarded as representing essentially the arrangement of the electrons in the atom. (Lewis, 1923, pp. 29–30, emphasis added)