Discussion of Pauli exclusion principle, and the connection of quantum mechanics to the periodic table and chemistry. Fermions obey the exclusion principle.
Fermions are spin odd half integer, bosons are integer spin.
Comes from antisymmetry of fermion wave function, symmetry of boson wave function. An example of using wave functions, and an introduction to an important concept. Let's see how to modify the ground state energy of hydrogen, based on the knowledge that the nucleus is not really a point, it has a finite size. We could try to start from scratch, with the modified potential, taking into account that the charge of the nucleus is not at a point. Instead, we'll make a sequence of approximations, and get a very decent guess.