What are the three rules that govern the filling of atomic orbitals by electrons

Rule 1. aufbau rule - energy levels filled so lowest energy level filled first.

Rule 2. pauli exclusion principle - maximum of 2 electrons may be placed in each energy level. Provided the spins of electrons are of opposite sign.

Rule 3. hunds rule - when energy levels are equal one electron is added to each energy level in turn with their spins unpaired until each energy level has one electron.