Henry Moseley quantitatively justified the concept of atomic number

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November 23, 1887, in Weymouth (United Kingdom) – August 10, 1915, in the Gallipoli Peninsula (Ottoman Empire)

Henry Gwyn Jeffreys Moseley entered in 1910 he graduated in Physics and Chemistry from Trinity College, Oxford University and then went to Oxford University to work with Ernest Rutherford. In principle, he taught more than he did research, however, a year later, he began to have more and more time to devote to science.

In 1914, he decided to return to Oxford with the intention of continuing his research career, but the First World War arose and he enlisted in the Royal Engineers division. He was posted to Gallipoli where, in 1915, he was shot in the head by a sniper while telegraphing an order. He died at the age of 27.

Historians agree that his work was already worthy of a Nobel Prize, however, it is only awarded to living researchers. There is speculation that Moseley's death is the reason the British government banned leading scientists from enlisting in the army during wartime.

His main contribution to science was, in advanced chemistry, providing fundamental support for the Bohr atomic model defined in detail by Rutherford and Antonius van den Broek, mentioning that atomic nuclei contain positive charges equal to their atomic number.

By indication of the latter, he studied the X-ray spectra of fifty elements and was able to quantitatively justify the concept of atomic number by means of Moseley's Law. Postulated in 1913, this empirical law states that the square root of the frequency of X-rays produced when an element is bombarded with cathode rays is proportional to the element's atomic number.

Until then, the atomic number was just the place an element occupied in the periodic table. This place had been associated to each element in a semi-arbitrary way by Mendeléiev and was quantitatively related to the properties of the elements and their atomic masses.

This is the basis of the periodic table and states that the physical and chemical properties of chemical elements tend to repeat themselves systematically as the atomic number increases.

In the opinion of many scientists, if he had lived longer, he could have contributed to more detailed knowledge of the structure of matter.

“It can be seen today that Rutherford's work on the atomic nucleus would not have been taken seriously. We wouldn't have understood it today either if we hadn't had Moseley's research." Niels Bohr (1962)

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