Hund's Rule and Orbital Filling

Fill equal-energy orbitals singly with parallel spins before pairing electrons.

Element examples

Active subshell2p

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Hund's RuleReady

Aufbau: lower-energy orbitals fill first.

Pauli: one orbital holds at most two electrons, and paired electrons have opposite spins.

Hund: equal-energy orbitals receive one electron each with parallel spins before any pairing begins.

Think of electrons choosing empty seats in a row before sharing a seat.

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