Then came a shock. On March 1 — two weeks after Pauling submitted his new work but a month before it was published — a paper appeared in the Physical Review that covered much of the same ground, including the idea of maximum overlapping of wave functions to create the most stable bonds; a discussion of the relationship between ionic and covalent bonds; a description of how, in compounds where there are several ways of drawing valence bonds, it was likely that "the real situation is . . . a combination of the various possibilities, and on account of resonance the energy is lower than it would otherwise be"; and, most important, an explanation of the tetrahedral bond in carbon. The author was John Slater, the young physicist whose work had helped to inspire Pauling's breakthrough.

It looked at first as though Slater had beaten Pauling. But after reading it several times, Pauling found some important differences in their work. Slater's paper, for one thing, was more descriptive than quantitative; it did not provide a way to get hard numbers for bond strengths and lengths. Pauling dashed off a note to the Physical Review calling readers' attention to his JACS paper's "very simple but powerful approximate quantitative treatment of bond strengths," briefly sketching his six rules, and stressing that it was he who had first put forward the quantum-mechanical approach to tetrahedral binding in 1928. (Slater had not referred to Pauling's earlier paper in his own work.) Pauling then quickly reviewed Slater's work and pointed out ways in which his own ideas went further.