systems, like molecules (for smaller molecules in practice, and for larger mol-
ecules at least in theory). Because this is far more than the classical theories of
chemistry and physics could provide, quantum mechanics is accepted as the
superior theory of the behavior of matter at the electronic level. The postulates
of quantum mechanics allow for some seemingly unusual and unexpected be-
havior—like tunneling, quantized angular momenta, and “fuzzy” electron or-
bitals. But so far, the predictions of quantum mechanics have been borne out
when examined experimentally. That is the true test of a theory.366 CHAPTER 11 Quantum Mechanics: Model Systems and the Hydrogen Atom