3.8 Aufbau Principle
The Aufbau principal guides on how electrons fill orbital shells. It states that when electrons are filling shells, they will fill the lowest energy orbitals first. The principal quantum number describes the energy associated with the orbital shells, with the lowest principal quantum number having the lowest energy level. Within a shell, each shape of orbital also has an energy associated with it, due to electron repulsion forces. The s shaped orbitals (l = 0) have the lowest energy associated, with the p shaped orbitals (l = 1) having the next highest energy, the d shaped orbitals (l = 2) having the next highest, and for the purpose of this class, the highest-level shape is the f shaped orbitals (l = 3).