How many quarks are in an electron?

An electron contains no quarks. It is classified as an elementary lepton in the Standard Model, while quarks are a separate class of elementary particles that combine to form composite particles such as protons and neutrons.

The electron was identified as a subatomic particle by J. J. Thomson in 1897. It carries one unit of negative electric charge and has a mass of about 0.511 MeV/c². Unlike a proton, it has no known smaller constituents.

A common mix-up is confusing the electron with the proton. A proton contains three valence quarks—two up quarks and one down quark—while a neutron contains one up quark and two down quarks. Electrons instead belong to the lepton family, alongside the muon, tau, and three neutrinos.

Physicists continue to test whether apparently elementary particles have deeper structure, but no quark content or internal substructure has been experimentally established for the electron.