Partial Ionic Character and Deformation

Partial Ionic Character and Deformation.—We have so far considered only structures for the hydrogen molecule in which the two 

One of the most important rules about resonance is that resonance can occur only among structures with the same number of unpaired electrons. Since the electrons in the negative hydrogen ion, occupying the same orbital, are paired and the electrons involved in a bond formed by structures I and II are paired, this condition is satisfied, and we expect structures III and IV as well as I and II to be of significance for the normal hydrogen molecule. 

At large internuclear distances the ionic structures III and IV are not of importance. The energy of the reaction 

James and A. S. Coolidge, /. Chem. Phye. 1, 825 (1933). Highly accurate calculations for the ground states of two-electron atoms from H to Nea+ have been made by C. L. Pekeris, Phye. Rev. 112, 1649 (1958). 

As a summary of the results reported above, the bond in the hydrogen molecule may be described as resulting in the main from the resonance of the two electrons between the two nuclei, this phenomenon contributing 80 percent of the total bond energy. An additional 5 percent is contributed by the ionic structures H H+ and H+H , which are of equal importance. The remaining 15 percent of the energy of the bond can be ascribed to complex interactions included under the term deformation.11 

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