An introduction to the fundamental principles and applications of quantum physics. The semester begins with a review of the experimental evidence for the quantization of energy, the particle and wave properties of matter, and the early quantum picture of the atom as discussed in Physics III (Modern Essentials). Wave mechanics is then developed in an elementary way, but in sufficient detail to provide a semiquantitative description of the structure and spectra of one-electron atoms and other single particle systems. These methods are extended to the description of many-electron atoms and molecules. Many-particle systems are described using both classical and quantum statistics.