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Pauli exclusion principle
Intermediate
No two fermions share the same quantum state.
No two identical fermions can occupy the same quantum state. It builds atomic shells and prevents the collapse of white dwarfs and neutron stars.
Helium's two electrons have opposite spins.
Only for identical fermions.
In more detail
The Pauli exclusion principle states that no two identical fermions can occupy the same quantum state. It explains the structure of atoms and the stability of matter.
Real-world uses
- It determines the electron configurations of atoms and the periodic table.
- It keeps white dwarfs and neutron stars from collapsing.
- Chemists use the Pauli principle to explain why electrons fill shells in a particular order and why matter is solid.
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Frequently asked questions
Does it apply to all particles?
It applies to fermions such as electrons, protons and neutrons, not bosons.
Why is it so important?
Without it, all electrons would collapse into the lowest orbital.
Why do electrons not all fall to the lowest level?
Each quantum state can hold only one electron, so electrons must occupy higher states once the lower ones are filled.
Related topics in Quantum Mechanics
Atomic orbitals · Electron spin · Stern–Gerlach experiment · Fermions and bosons · Identical particles · Angular momentum in QM