10-16 meters = 100 attometers
Until the 1960s, protons, neutrons, and electrons were considered elementary particles making up the atom. The nucleus of the atom contained the protons and neutrons, and the electrons orbited the nucleus in distinct energy bands. In the subsequent years, scores of higher energy, unstable particles were discovered in particle colliders throughout the world. Eventually, theories were developed that demoted the proton and neutron from the class of elementary particles. It has been determined that protons and neutrons are made up of more basic particles called quarks. Quarks, along with electrons and neutrinos, are now thought to be truly elementary, in that they have no internal structure.