Hund’s Rule sounds like the kind of “small” fact you can postpone until later. Then an exam question appears, you draw three little boxes, and suddenly your brain tries to bargain with physics.
In IB Chemistry, that moment matters. Hund’s Rule quietly supports electron configuration, periodic trends, and magnetic properties. And because it’s both visual (orbital diagrams) and conceptual (stability), it’s exactly the kind of rule examiners like to test under time pressure.
Quick checklist for Hund’s Rule in IB Chemistry
Keep this on a sticky note for IB Chemistry revision:
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Hund’s Rule applies to degenerate orbitals (same energy) like p, d, and f.
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Electrons fill singly first across the set.
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Single electrons in separate orbitals have parallel spins.
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The pattern lowers energy by reducing electron-electron repulsion and increasing stability.
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The number of unpaired electrons helps predict magnetic behaviour.
If you want a bigger revision structure around this, borrow a weekly routine from The Ultimate Guide to Revision for IB Students.
What Hund’s Rule actually says (and what “degenerate” means)
Hund’s Rule states that electrons occupy orbitals of equal energy one at a time before any pairing happens, and those unpaired electrons have parallel spins.
In IB Chemistry, “degenerate” just means “same energy.” The classic examples are:
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the three 2p orbitals (p_x, p_y, p_z)
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the five 3d orbitals
So when you’re filling a p subshell, you don’t complete one box before touching the next. You “spread out” first.
For syllabus-aligned detail and examples, RevisionDojo’s notes on IB Chemistry S1.3.5 Orbital Configurations and Rules are a clean place to lock it in.
Why electrons spread out first (the stability story)
Two electrons in the same orbital must be close together and must have opposite spins. Close together means more repulsion. Pairing too early raises energy.
Hund’s Rule is the atom’s preference for a calmer arrangement: occupy separate, equal-energy orbitals first so electrons can keep their distance. The payoff is a more stable configuration.
This is why IB Chemistry questions about nitrogen and oxygen tend to show up:
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Nitrogen ends 2p³: three orbitals, three electrons, all unpaired.
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Oxygen ends 2p⁴: one orbital becomes paired, two remain unpaired.
If your electron configurations feel shaky, use the bigger topic hub IB Chemistry S1.3 Electron configurations and then reinforce it with targeted practice.
Hund’s Rule in orbital diagrams (common exam traps)
Orbital diagrams are where IB Chemistry becomes very literal: marks are often lost for a single misplaced arrow.
The exam-safe method
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Draw one box per orbital.
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Place one ↑ in each box before adding any ↓.
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Only then start pairing with ↓ (opposite spin).
Typical mistakes examiners love
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Pairing in the first orbital while the other degenerate orbitals are empty.
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Forgetting that paired electrons must have opposite spins.
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Confusing filling order rules: Aufbau decides which subshell first, Hund decides how to fill within a subshell.
To train this properly, do short bursts of exam-style questions instead of re-reading. RevisionDojo’s S1.3 Electron configurations Questionbank is built for exactly these patterns.
Hund’s Rule and magnetism in IB Chemistry
Magnetism questions feel like they came from nowhere until you remember one phrase: unpaired electrons.
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Paramagnetic substances have unpaired electrons and are weakly attracted to a magnetic field.
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Diamagnetic substances have all electrons paired and are weakly repelled.
In IB Chemistry, you’re often asked to justify the behaviour using an orbital diagram. It’s not about sounding advanced. It’s about being specific: “There are two unpaired electrons, therefore paramagnetic.”
For the “electron configuration meets periodic trends” side of this, S3.1.2 Electron configuration and group trends helps connect the dots the way exam questions do.
A simple way to revise Hund’s Rule without burning time
Hund’s Rule is small enough to revise daily, but important enough to keep returning to.
A good IB Chemistry loop:
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Study Notes: read one tight explanation (2-5 minutes).
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Flashcards: one card for the rule, one for “degenerate orbitals,” one for “paramagnetic vs diamagnetic.”
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Questionbank: 10 quick configuration/orbital diagram questions.
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AI Chat: ask why your diagram loses marks, then retry immediately.
If the bigger IB workload is the real problem, How to Study for IB Exams: Step-by-Step Guide is a solid reset.
Conclusion: the quiet rule that saves marks in IB Chemistry
Hund’s Rule is simple, but it isn’t trivial. In IB Chemistry, it’s one of those rules that turns confusion into a repeatable method: fill degenerate orbitals singly, keep spins parallel, then pair. Once you can do that automatically, electron configurations, orbital diagrams, and magnetic property questions become predictable instead of stressful.
If you want to make that predictability your default, build a loop inside RevisionDojo: learn with Study Notes, drill with Flashcards, apply with the Questionbank, get unstuck with AI Chat, and pressure-test with Mock Exams and Predicted Papers. Add the Grading tools for written explanations, and the Coursework Library plus Tutors when you want examples or a human walkthrough. That’s how IB Chemistry stops being a pile of facts and becomes a system you can run on exam day.