Henry Moseley (jan 1, 1913 – jan 1, 1913)

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Henry Moseley was an English physicist discovered that the atomic number is the most fundamental property of an element, not its atomic mass.

To address the limitations in Mendeleev's chart, Moseley organized the elements in the periodic table in ascending order of atomic number. For example, hydrogen has atomic number of 1 and helium has atomic number of 2.

Through the use of X-ray spectroscopy, he was able to determine the atomic numbers of each element. He measured the wavelength of the X-rays produced by firing samples of the elements with the recently invented X-ray gun. He was able to determine each element's atomic number by applying the law he created, Moseley's law. In addition, Moseley's work suggested the existence of four newly found chemical elements, supporting his idea regarding the arrangement of atomic numbers.

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