‘Quantum mechanics’ shows how Bohr’s quantum theory was a stepping stone for the development of quantum mechanics. Bohr’s quantum theory worked well in single electron systems, but not in multi-electron systems. Quantum mechanics allowed the development of Schrödinger’s equation, which could theoretically predict the determination of electron energy levels in any system. The advantage of quantum mechanics over quantum theory lies in its treatment of electrons as waves. This allowed Schrödinger to apply mathematical boundary conditions to his equation and quantize the energy levels of electrons. Further work by Heisenberg showed that electrons are spread around a spherical shell. New developments on atomic configurations by Eugen Schwarz are also discussed.