Leptons and quarks constitute the smallest particles of matter, based on contemporary evidence in the field of particle physics. Traditionally, the atom was considered as the indivisible form of matter.
Atoms were once believed to be comprised of only three subatomic particles: protons, electrons and neutrons. However, in the 1960s, several other particles were discovered. The quarks are involved in strong interactions, while the leptons are unaffected by the strong force. The different types of quarks are called top, bottom, up, down, strange and charm, while the leptons are classified into electron neutrino, muon neutrino, tau neutrino, electron, muon and tau. The atom also consists of force-carrier particles known as photon, gluon, W boson and Z boson.