Henry Gwyn-Jeffreys Moseley, was an important chemist and physicist, born in 1887 in Weimouth, England. It was he who proposed the atomic number of the atoms of the elements. He worked together with Ernest Rutherford. Studied at Oxford and became Rector of Physics at Cambridge University. It was at this university that he collaborated with Rutherford.

He conducted studies on X-ray spectroscopy. In 1900, Moseley studied X-ray emission from atoms that had been bombarded by an electron beam. It concluded that this emission was linked to an integer value of positive charges in the atomic nucleus.

He found that atoms of different elements have different numbers of positive charge in the nucleus. The value of this charge is the known atomic number, which characterizes the chemical elements.

Around 1903, it determined the wavelengths of alpha radiations of various elements and obtained a relationship between the wavelengths of the considered radiation and the atomic numbers of the elements that emit them.
Moseley's discovery was important for the periodic classification of the elements.

Moseley showed the existence of gaps that should be filled in the periodic table. The current table has the same configuration as Moseley's time. Moseley died in a World War I combat in Turkey in 1915.