Antonius van den Broek

Antonius van den Broek (May 4, 1870 - October 25, 1926) was a Dutch amateur physicist (a real estate lawyer by training). He is notable mostly for being the first who realized that the number of an element in the Periodic table corresponds to its total number of electrons and protons and therefore the charge of the atom nucleus.

This idea was contained in his paper published in "Nature" on July 20, 1911, just one month after Rutherford published the results of his experiments that showed the existence of a small charged nucleus in an atom. However, Rutherford's original paper noted only that the charge on the nucleus was large, on the order of about half of the atomic weight of the atom, in whole number units of hydrogen mass. Rutherford on this basis made the tentative suggestion that atomic nuclei are composed of numbers of helium nuclei, each with a charge corrsponding to half of its atomic weight. This would make the nuclear charge nearly equal to atomic number.

Rutherford did not actually go so far as to make the implied proposal that the number of charges in the nucleus of an atom might be "exactly" equal to its place on the periodic table (atomic number). This place or number at that time was not thought by most physicists to be a physical property, and it was not until the work of Henry Moseley that it was realized atomic number was indeed a physical property, and that Van den Broek's original guess had been correct.