This morning I stumbled on a set of three videos of lectures given by the great 20th century physicist Hans Bethe. In the first lecture, which lasts about 50 minutes, he discusses the old quantum theory. This lecture covers Planck and his black body curve and ends with a discussion of the hydrogen atom as described by Neils Bohr.
In the second lecture, he discusses the development of modern quantum mechanics by Heisenberg and others.
In the third and final lecture, Bethe talks about some of the interesting results that have sprung up from quantum theory that make it so interesting, like the Heisenberg uncertainty principle and spooky action at a distance.