Hund's rule
The key idea
Hund’s rule describes the lowest-energy filling pattern within a set of degenerate orbitals: electrons occupy different orbitals with parallel spins before pairing, in the usual atomic model.
Why it matters
It helps explain ground-state electron configurations and magnetic behaviour, but it belongs to a broader quantum-mechanical energy picture.
A picture to remember
It helps explain ground-state electron configurations and magnetic behaviour, but it belongs to a broader quantum-mechanical energy picture.