11.7: The Big Picture

In this part of the course, we’ve discussed now how the basics of quantum mechanics apply to molecular systems. In particular we’ve found that no one knows how to solve the Schrödinger equation analytically for any molecule, but have introduced several approximations that help us get a handle on how chemical bonding and molecular structure come about. We’ve discussed brute-force ab-initio methods of solving the Schrödinger equation, and discussed some of the tradeoffs inherent in calculations. Finally, we talked about a couple approximate methods, hybridization and Hückel theory, that can give us quick ideas about structure and energetics in special cases, at the expense of accuracy and (sometimes) fidelity to reality. Armed with all of these tools, we now have a conceptual understanding of the electronic structure of molecules and how chemical bonding works. We have not yet looked at the internal degrees of freedom for molecules, so we don’t know anything about molecular vibration or rotation in polyatomic molecules. We will study those later as we learn more about spectroscopy, because those topics are intimately linked. But first, we will take a look at the connection between symmetry and quantum mechanics, which will in turn lead naturally to spectroscopy.

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