Neutrons and protons are the components of the nuclei. Both have the same mass (1.67·10-27 kg) but neutrons are electrically neutral while protons have a positive charge. Usually but not always the number of neutrons in a nucleus is identical with the number of protons. Neutrons and protons together determine the mass of the atoms. This means that the heavier the atom, the more neutrons there are in the nucleus. Neutrons were discovered in 1932 by Sir James Chadwick.