Spin Quantum Number
The quantum number mₛ describing the intrinsic angular momentum of an electron, restricted to +½ or −½.
Formula / equation
mₛ = ±½
Unit
Dimensionless
In depth
Electron spin is a purely quantum property with no classical analogue, first demonstrated by the Stern–Gerlach experiment. Because only two spin states exist, an orbital can hold at most two electrons. Unpaired spins give rise to paramagnetism and to the signals detected in EPR and NMR spectroscopy.
Examples in the real world
Helium's two 1s electrons occupy the same orbital with opposite spins, written 1s².