Today in chemistry I learned about new principles relating to electrons. The Aufbau principle states that electrons occupy the orbitals of lowest energy first. Pauli Exclusion principle is an atomic orbital may describe at most two electrons. Hunds rule is that electrons occupy orbitals of the same energy in a way that makes the number of electrons with the same spin direction as large as possible. You should always put parallels spins before pairing electrons:
Spin is a quantum mechanical property of electrons and may be thought of as clockwise or counterclockwise.
I also learned that half-filled sub levels are not as stable as filled sublevels but are more used because they’re more stable than other configurations.