We are finally ready to discuss molecules. As we did for atoms, we will consider first the simplest cases to derive some results on which to build. From these we will generalize to obtain rules to be used in the more complicated cases, for which we will not explicitly carry out calculations. The simplest cases are H2+(two protons and one electron) and H2 (two protons and two electrons). Our main goal is to find out what makes these molecules stable, that is, why the energy of H2 is less than the energy of two separated hydrogen atoms. We will then be interested in discussing what determines interatomic (bond) distances, what makes some bonds stronger than others, and so on.
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