atoms behaved in the manner described by Newton, and they don’t. Individual
electrons and atoms require a different model to explain their behavior.
Most basic quantum mechanics was developed by 1930. However, the de-
velopment of quantum mechanics as applied to electrons also led to new the-
ories of the nucleus, all of which today inherently contain quantum assump-
tions. Today, quantum mechanics encompasses the entire behavior of the
atom. Because chemistry starts with atoms, quantum mechanics provides the
very basis of modern chemical science.270 CHAPTER 9 Pre-Quantum Mechanics