Resonance between valence configurations or mesomerism

The concept of resonance was developed above as the basis for the atomic bond. In so doing the wave function, which must describe the electrons in H2+ and H2, was constructed by the combination of functions that describe separate configurations, which are distinguished from each other by place exchange (H2+) or exchange (H2) of electrons. 

Now this multiplicity of the electron configuration occurs not only in the bonding between two atoms but also in many cases in which one can compose for the whole molecule more than one electron formula, which thus represent different electron configurations. 

We use here throughout the term configurations as far as different arrangements of electrons are concerned, while by the term structure a spatial arrangement of the atomic nuclei is indicated. Contrary to the latter, the separate configuration has no real physical meaning. 

It may again be emphasized that neither resonance nor the separate configurations possess any physical significance (p. 130). Thus it is also incorrect to speak here of an equilibrium between two or more forms of molecule, or to imagine that the molecule occurs now in the one, now in the other configuration. This is the distinction with tautomerism, in which the struc- 

Resonance is furthermore only possible, at any rate of significance for the energy, between electron configurations of the same spatial nuclear structure. As shown (p. 128) the split- 

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