 The 331 model in particle physics is an extension of the electroweak gauge symmetry from formula_2 to formula_3 with formula_4.In the 331 model, hypercharge is given by

and electric charge is given by

where formula_7 and formula_8 are the Gell-Mann matrices of SU(3) and formula_9 and formula_10 are parameters of the model.The 331 model offers an explanation of why there must be three families of quarks and leptons.