High Quality Content by WIKIPEDIA articles! The proton is a subatomic particle with an electric charge of +1 elementary charge. It is found in the nucleus of each atom, along with neutrons, but is also stable by itself and has a second identity as the hydrogen ion, H+. It is composed of three fundamental particles: two up quarks and one down quark.Protons are spin- fermions and are composed of three quarks, making them baryons. The two up quarks and one down quark of the proton are held together by the strong force, mediated by gluons. The proton has an approximately exponentially decaying positive charge distribution with a mean square radius of about 0.8 fm.