Antonius Johannes van den Broek (4 May 1870 – 25 October 1926) was a Dutch mathematical economist and amateur physicist, notable for being the first who realized that the position of an element in the periodic table (now called atomic number) corresponds to the charge of its atomic nucleus.

The idea of the direct correlation of the charge of the atom nucleus and the periodic table was contained in his paper[1] published in Nature on 20 July 1911, just one month after Ernest Rutherford published the results of his experiments that showed the existence of a small charged nucleus in an atom (see Rutherford model).

For example, Rutherford found the charge on gold to be about 100 units and thought perhaps that it might be exactly 98 (which would be close to half its atomic weight).

It was not until the work of Henry Moseley working with the Bohr model of the atom with the explicit idea of testing Van den Broek's hypothesis, that it was realized that atomic number was indeed a purely physical property (the charge of the nucleus) which could be measured, and that Van den Broek's original guess had been correct, or very close to being correct.

Henry Moseley, in his paper on atomic number and X-ray emission, mentions only the models of Rutherford and Van den Broek.