Fermions and Bosons Particles can be divided into two classes on the basis of their spins. Bosons are particles with integer spin in h-bar units. You may be familiar with this type of rule for electrons in atoms. Bosons do not follow such a rule and, in a certain sense, favor states with many particles in the same state. Baryons are made from odd numbers of quarks and so are fermions.
Mesons also are bosons.