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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Spin quantum number

The quantum number msm_s, either +12+\tfrac{1}{2} or −12-\tfrac{1}{2} ("up" or "down"), that describes an electron's spin, an intrinsic property that makes it behave like a tiny magnet. Two electrons in the same orbital must have opposite spins.

Helium: one orbital, two electrons of opposite spin.

Example

Helium's two electrons are (1,0,0,+12)(1, 0, 0, +\tfrac{1}{2}) and (1,0,0,−12)(1, 0, 0, -\tfrac{1}{2}); a third electron cannot enter 1s because no third value of msm_s exists.

See alsoQuantum numbersPauli exclusion principleParamagnetic