The periodic table of elementary particles, represented by the Standard Model, includes, as we saw in Chap.  2 , six particular elements, the leptons. Three of these are particles endowed with mass and charge, the electron (e), the muon (or mu) (μ), and the tau (τ); three others are their respective neutrinos, νe, νμ, ντ, without charge, with virtually negligible mass and spin 1/2. These particles have their equivalent in antimatter, so in total between leptons and antileptons there are twelve elements in the Standard Model. The electron in the table is placed in the first column and is thus a first-generation particle; the muon and tau, on the other hand, belong to the second and third generations, respectively. Each generation is completed by a pair of quarks. There are six quarks in all, plus the six antiquarks.