Absolutely Small, Chapter 9: The Hydrogen Atom, The History

The hydrogen atom is the simplest atom. Its properties confounded physicists and chemists who tried to explain it with classical mechanics. This chapter discusses the early attempts to explain the hydrogen atom. What people saw that was confusing. For example, it describes how sunlight has some missing colors. This is caused by the absorption of light by hydrogen atoms in space. The fact that hydrogen only absorbs certain discrete colors could not be explained prior to the advent of quantum theory.