Hund's third rule

Hund's third rule states that when electrons occupy orbitals with the same energy (degenerate orbitals), the atom's overall lowest energy state is achieved by maximizing the total angular momentum. Specifically, for electrons with parallel spins, the total angular momentum quantum number is as large as possible, which results in a more stable, lower-energy configuration. In simple terms, electrons prefer to occupy different orbitals with the same spin before pairing up, and their combined magnetic effects influence the atom's energy, favoring arrangements that enhance net magnetic properties and stability.