1914 Manchester, England

‘Moseley’s law – the principle outlining the link between the X-ray frequency of an element and its atomic number’

Working with ERNEST RUTHERFORD’s team in Manchester trying to better understand radiation, particularly of radium, Moseley became interested in X-rays and learning new techniques to measure their frequencies.
A technique had been devised using crystals to diffract the emitted radiation, which had a wavelength specific to the element being experimented upon.

In 1913, Moseley recorded the frequencies of the X-ray spectra of over thirty metallic elements and deduced that the frequencies of the radiation emitted were related to the squares of certain incremental whole numbers. These integers were indicative of the atomic number of the elements, and therefore their position in the periodic table. In addition, this number was the same as the positive charge of the nucleus of an atom (and by implication also the number of electrons with corresponding negative charge in an atom).

By uniting the charge in the nucleus with the atomic number, and therefore the element’s position in the periodic table, a vital link had been found between the physical atomic make up of an element and its chemical properties, as indicated by its position in the periodic table.
This meant that the properties of an element were now considered in terms of atomic number rather than atomic weight, as had previously been the case – certain inconsistencies in the MENDELEEV version of the periodic table could be ironed out. In addition, the atomic numbers and weights of several missing elements could be predicted and other properties deduced from their expected position in the table.

picture of the Nobel medal - link to nobelprize.org