Beginner Topic 63 of 1102 Atomic Structure & Periodicity
Hund's Rule
Electrons occupy degenerate orbitals singly with parallel spins before pairing up.
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In-depth explanation of Hund's Rule
Hund's rule states that electrons occupy degenerate orbitals singly, with parallel spins, before any pairing occurs within the same orbital. This arrangement minimises electron-electron repulsion and maximises the exchange energy, which stabilises the atom. It explains why nitrogen has three unpaired electrons in its 2p subshell. It also determines the ground-state multiplicity and magnetic properties of atoms and ions. The rule applies to orbitals of equal energy within a subshell.
Going deeper: Hund's Rule
Key ideas: Within a subshell, electrons occupy separate orbitals with parallel spins before pairing (maximum multiplicity). For p3 (N), draw three up arrows in px, py, pz. This lowers repulsion and gains exchange energy. Unpaired electron count predicts paramagnetism: Fe with 4 unpaired electrons in 3d6.
Common mistakes and connections: Students pair electrons early in the p or d subshell, or put parallel spins in the same orbital (impossible due to Pauli). Hund's rule applies to degenerate orbitals only. It explains the high stability of half-filled subshells and the ionization energy dip from N to O.
Visualization of Hund's Rule
Electrons fill p orbitals singly first, so unpaired electrons peak at 3 for nitrogen (p3) before pairing reduces the count to 0 for neon. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Carbon has a 2p2 configuration, with its two p electrons in different orbitals and with parallel spins.
Frequently asked questions about Hund's Rule
What is Hund's Rule?
Electrons occupy degenerate orbitals singly with parallel spins before pairing up.
Is Hund's Rule a beginner, intermediate or advanced topic?
Hund's Rule is a beginner topic in Atomic Structure & Periodicity. It needs no earlier chemistry lessons and is a good starting point.
What should I learn before Hund's Rule?
Study these earlier topics in Atomic Structure & Periodicity first: Electron Shells and Subshells, Aufbau Principle, Pauli Exclusion Principle.
What comes after Hund's Rule?
The next topics in Atomic Structure & Periodicity are Madelung Rule and Electron Configuration.
Can I practise Hund's Rule with quizzes?
Yes. The interactive lesson includes a self-check question on Hund's Rule, and the Atomic Structure & Periodicity quiz draws on every topic in this area.
Where Hund's Rule fits in Atomic Structure & Periodicity
Hund's Rule is topic 63 of 115 in Atomic Structure & Periodicity.