Ten years later, the British physicist Ernest Rutherford discovered that atoms have a very dense nucleus that contains protons. In 1932, another British physicist, James Chadwick, discovered the neutron, another particle located within the nucleus. With the electron, proton, and neutron, scientists thought they had found the smallest atomic building blocks. This changed in 1963 when American physicist Murray Gell-Mann proposed his quark theory. Physicists have learned a great deal over the past 100 years.
Neutrons have no charge.