What Is Hund’s Rule
What Is Hund’s Rule?
Hund’s rule tells us how electrons fill the space around an atom.
It says that electrons spread out first before they pair up.
Imagine you’re sitting on a bus. You take an empty seat before sitting next to someone else, right?
Electrons act the same way — they like space.
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| What Is Hund’s Rule |
The Simple Definition
When electrons fill orbitals of the same energy, they go one by one before sharing a spot.
This way, electrons stay apart and reduce push between them. That makes the atom more stable.
How Hund’s Rule Works with Other Rules
Hund’s rule works with two other rules that describe how electrons fill orbitals:
Together, they explain how electrons fill atoms in the simplest way.
Why This Rule Is Important
Hund’s rule helps explain:
✅ Why atoms are stable.
✅ Why some materials are magnetic.
✅ How atoms bond with each other.
When electrons stay unpaired, atoms often show magnetism.
When all electrons are paired, the atom is non-magnetic.
Examples
Example 1: Carbon (6 electrons)
Configuration: 1s² 2s² 2p²
Filling order: ↑ ↑ _
Each 2p orbital gets one electron before any pairs form.
Example 2: Nitrogen (7 electrons)
Configuration: 1s² 2s² 2p³
Filling order: ↑ ↑ ↑
All three orbitals get one electron each, all with parallel spins.
Example 3: Oxygen (8 electrons)
Configuration: 1s² 2s² 2p⁴
Filling order: ↑↓ ↑ ↑
Here one orbital gets paired, but two still remain unpaired.
These examples show how Hund’s rule helps organize electrons to keep energy low and the atom stable.
How Hund’s Rule Explains Magnetism
Atoms with unpaired electrons → magnetic (paramagnetic)
Atoms with all paired electrons → non-magnetic (diamagnetic)
Example:
Nitrogen → 3 unpaired → Paramagnetic
Oxygen → 2 unpaired → Paramagnetic
Neon → 0 unpaired → Diamagnetic
Hund’s Rule in d and f Orbitals
The same rule works for d and f orbitals:
Iron (Fe): 4 unpaired electrons → magnetic
Manganese (Mn): 5 unpaired electrons → strongly magnetic
Nickel (Ni): 2 unpaired electrons → weakly magnetic
Hund’s rule explains all these cases in the same simple way — electrons fill singly first.
Exceptions to Hund’s Rule
Most atoms follow the rule, but some don’t.
These are usually transition metals where orbital energies shift slightly.
Example:
Chromium (Cr) – Expected: [Ar] 4s² 3d⁴ → Actual: [Ar] 4s¹ 3d⁵
Copper (Cu) – Expected: [Ar] 4s² 3d⁹ → Actual: [Ar] 4s¹ 3d¹⁰
Why?
Because a half-filled or fully-filled orbital is more stable.
How to Remember Hund’s Rule
Tip:
“Electrons hate company until there’s no choice.”
That’s Hund’s rule in one line.
Everyday Importance
Hund’s rule may sound tiny, but it affects our world:
🧲 Magnetism in metals and MRI machines
🌈 Colors in fireworks and chemical reactions
⚛️ Stability of elements in the periodic table
So this rule helps explain both science and the things we see every day.
Frequently Asked Questions (FAQ)
Q1. What is Hund’s rule in simple words?
➡ Electrons fill orbitals one at a time before pairing.
Q2. Why is it important?
➡ It keeps atoms stable and explains magnetism.
Q3. Who discovered it?
➡ German scientist Friedrich Hund in the 1920s.
Q4. Is Hund’s rule always true?
➡ Almost always, but some transition metals are exceptions.
Q5. What’s a real-world effect?
➡ It explains magnetic behavior and how atoms bond.
Conclusion
The Hund’s rule shows us a simple truth — electrons like space.
They stay apart until there’s no room left, helping atoms stay balanced and stable.
This rule links directly to magnetism, bonding, and atomic structure — the foundation of chemistry.
It’s a small rule with a big impact!
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