Scientist Discovery Electron J.J. Thomson Proton Ernest Rutherford Neutron James Chadwick Atomic Nucleus Ernest Rutherford The nucleus of a cell Robert Brown Note: J J Thomson discovered cathode rays, known as electrons, experimentally and Goldstein discovered positive rays, which were named as protons by Rutherford. In 1932, James Chadwick discovered the charge less particles called neutrons. Presently, a large number of elementary particles like photon, meson, positron and neutrino have been discovered. In 1911, the British scientist, Ernest Rutherford explained that the mass of an atom is concentrated in its central part called Nucleus.