The electron (
e −
or
β −
) is a subatomic particle with a negative one elementary electric charge.
Electrons belong to the first generation of the lepton particle family, and
are generally thought to be elementary particles because they have no known
components or substructure. The electron's mass is approximately 1/1836 that
of the proton. Quantum mechanical properties of the electron include an
intrinsic angular momentum (spin) of a half-integer value, expressed in units
of the reduced Planck constant, ħ. Being fermions, no two electrons can occupy
the same quantum state, per the Pauli exclusion principle.