Antonius Van den Broek
Antonius Johannes van den Broek (4 May 1870, Zoetermeer
Zoetermeer is a city in the western Netherlands, in the province of South Holland. The municipality covers an area of 37.06 km² . A small village until the late 1960s, it had 6,392 inhabitants in 1950...

 - 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
Periodic table
The periodic table of the chemical elements is a tabular display of the 118 known chemical elements organized by selected properties of their atomic structures. Elements are presented by increasing atomic number, the number of protons in an atom's atomic nucleus...

 corresponds to the charge of its atomic nucleus.


Van den Broek was the son of a civil law notary
Civil law notary
Civil-law notaries, or Latin notaries, are lawyers of noncontentious private civil law who draft, take, and record legal instruments for private parties, provide legal advice and give attendance in person, and are vested as public officers with the authentication power of the State...

 and trained to be a lawyer himself. He studied at Leiden University
Leiden University
Leiden University , located in the city of Leiden, is the oldest university in the Netherlands. The university was founded in 1575 by William, Prince of Orange, leader of the Dutch Revolt in the Eighty Years' War. The royal Dutch House of Orange-Nassau and Leiden University still have a close...

 and at the Sorbonne
University of Paris
The University of Paris was a university located in Paris, France and one of the earliest to be established in Europe. It was founded in the mid 12th century, and officially recognized as a university probably between 1160 and 1250...

 in Paris
Paris is the capital and largest city in France, situated on the river Seine, in northern France, at the heart of the Île-de-France region...

, obtaining a degree in 1895 in Leiden. From 1895 to 1900 he held a lawyers office in The Hague
The Hague
The Hague is the capital city of the province of South Holland in the Netherlands. With a population of 500,000 inhabitants , it is the third largest city of the Netherlands, after Amsterdam and Rotterdam...

 until 1900, after which he studied mathematical economy in Vienna
Vienna is the capital and largest city of the Republic of Austria and one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.723 million , and is by far the largest city in Austria, as well as its cultural, economic, and political centre...

 and Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...

. 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
Gorssel is a village in the Dutch province of Gelderland. It is located in the municipality of Lochem, about 6 km southeast of Deventer.Gorssel was a separate municipality until 2005, when it was merged with Lochem....

. He married Elisabeth Margaretha Mauve in 1906, with whom he had five children.

Major contribution to science

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
Nature (journal)
Nature, first published on 4 November 1869, is ranked the world's most cited interdisciplinary scientific journal by the Science Edition of the 2010 Journal Citation Reports...

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
Rutherford model
The Rutherford model or planetary model is a model of the atom devised by Ernest Rutherford. Rutherford directed the famous Geiger-Marsden experiment in 1909, which suggested on Rutherford's 1911 analysis that the so-called "plum pudding model" of J. J. Thomson of the atom was incorrect...

). 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 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.

Thus Rutherford did not make the 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 is the idea put forward by van den Broek. The number of the place of an element in the periodic table (or atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...

) at that time was not thought by most physicists to be a physical property. It was not until the work of Henry Moseley
Henry Moseley
Henry Gwyn Jeffreys Moseley was an English physicist. Moseley's outstanding contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic number. This stemmed from his development of Moseley's law in X-ray spectra...

 working with the Bohr model
Bohr model
In atomic physics, the Bohr model, introduced by Niels Bohr in 1913, depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus—similar in structure to the solar system, but with electrostatic forces providing attraction,...

 of the atom with the explicit idea of testing van den Broek's theory, 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 correct. Moseley's work actually found (see Moseley's law
Moseley's law
Moseley's law is an empirical law concerning the characteristic x-rays that are emitted by atoms. The law was discovered and published by the English physicist Henry Moseley in 1913...

) the nuclear charge best described by the Bohr equation and a charge of Z-1, where Z is the atomic number
Atomic number
In chemistry and physics, the atomic number is the number of protons found in the nucleus of an atom and therefore identical to the charge number of the nucleus. It is conventionally represented by the symbol Z. The atomic number uniquely identifies a chemical element...


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


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