Leptons, like quarks, have half integer spin. Unlike quarks, leptons have integer charge, +1, 0, or -1. The most recognizable lepton is the electron, a first generation particle. It's anti-particle is the positron, also known as the anti-electron. The electron has a charge of -1, and the positron has a charge of +1. Since electrons have a negative charge, they are attracted to protons, and this allows complex configurations of matter to form on the macroscopic scale. The mass of both the electron and the positron are about 1/3 that of the up quark. The electron neutrino and electron antineutrino, both with a charge of 0, complete the first generation of leptons. The electron neutrino and electron antineutrino are each about a million times lighter than an up quark, though their mass has only been inferred indirectly, and have yet to be measured directly.
The second generation of leptons includes the muon (-1 charge) and its antiparticle (+1 charge), each about one hundred times more massive than an up quark, as well as the muon neutrino and the muon antineutrino which are about a tenth as massive as the up quark.
The third generation of leptons includes the tau lepton (-1 charge) and its antiparticle (+1 charge), nearly two thousand times as massive as the up quark. The third generation also includes the tau neutrino and the tau antineutrino which are nearly twenty times as massive as the up quark. All neutrinos and antineutrinos have a charge of 0.
Like the second and third generations of quarks, the second and third generation of leptons don't participate in the construction of everyday matter; they are produced in particle accelerators and in certain exotic situations in the universe.
