spin quantum number

The spin quantum number is a fundamental property of subatomic particles, representing their intrinsic angular momentum. Introduced in 1925 by Samuel Goudsmit and George Uhlenbeck, it was initially proposed to explain atomic spectra.12

Electrons, for instance, possess a spin quantum number that can have one of two values: -1/2 or +1/2. This intrinsic spin causes electrons to behave like tiny spinning charges, each generating a magnetic field and magnetic moment. This internal magnet can align either parallel or antiparallel to an external magnetic field, resulting in these two quantized states.1

The concept of spin is crucial for classifying particles into two main groups: fermions, which have half-integer spin values (like 1/2), and bosons, which have integer spin values (like 0 or 1). Matter particles such as quarks and leptons are fermions, while force-carrying particles like photons are bosons.1