Hund's Rule and Orbital Filling

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

Element examples

Build the orbital diagram

Active subshell2p

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Electron configuration

Complete orbital diagram

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Hund's RuleReady

Learning objectives

Apply the Aufbau principle, Pauli exclusion principle, and Hund's Rule.
Distinguish orbitals from subshells.
Predict unpaired electrons and magnetic behavior.
Construct p and d orbital diagrams.

Three rules work together

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.

Suggested experiments

Build carbon, nitrogen, then oxygen one electron at a time.
Try pairing carbon's two p electrons in one orbital and observe the warning.
Compare nitrogen and oxygen's unpaired electrons.
Explore iron's five d orbitals.

7-question challenge

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