Antonius van den Broek

Antonius Johannes van den Broek (4 May 1870, Zoetermeer – 25 October 1926, Bilthoven) was a Dutch amateur physicist notable for being the first who realized that the number of an element in the periodic table (now called atomic number) corresponds to the charge of its atomic nucleus. This hypothesis was published in 1911 and inspired the experimental work of Henry Moseley, who found good experimental evidence for it by 1913.

Van den Broek was the son of a civil law notary and trained to be a lawyer himself. He studied at Leiden University and at the Sorbonne in Paris, obtaining a degree in 1895 in Leiden. From 1895 to 1900 he held a lawyers office in The Hague until 1900, after which he studied mathematical economy in Vienna and Berlin. However, from 1903 on his main interest was physics. Much of the time between 1903 and 1911 he lived in France and Germany. Most of his papers he wrote between 1913 and 1916 while living in Gorssel. He married Elisabeth Margaretha Mauve in 1906, with whom he had five children.

The idea of the direct correlation of the charge of the atom nucleus and the periodic table 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 (see Rutherford model). 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 bass made the tentative suggestion that atomic nuclei are composed of numbers of helium nuclei, each with a charge corresponding to half of its atomic weight. This would make the nuclear charge nearly equal to atomic number in smaller atoms, with some deviation from this rule for the largest atoms, such as gold. 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). But gold's place in the periodic table (and thus its atomic number) was known to be 79.

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