Some details of four previously-published quantum-chemistry formulae are redescribed. These formulae relate to (a) Bohr circular orbits and the atomic shell-structure formula 2n², (b) the separation of variables for a two-electron atom,  (c) atomic valencies for a diatomic one-electron bond, and (d) Hartree-Fock energy, ionization potentials and Hückel-like orbital energies. A fifth formula, the Wiberg valence formula for an electron-pair bond, is expressed as a sum of covalent spin-pairing and charge transfer contributions. A formula for an electron transfer matrix element is also presented.