The Lewis occupancy is the total number of electrons residing in the orbitals (core, bonds, lone pairs) of the Lewis structure. The non-Lewis occupancy is the remaining amount of electron density that occupies Rydberg (RY*) and antibonding (BD*) orbitals. In this methylamine calculation, the electron density is well d escribed by the Lewis structure, failing to represent only 0.050 of 18 electrons.