Henry Moseley (1914)

The Discovery of the Atomic Number (and what it means)

In 1913 Henry Moseley was working at the University of Manchester when he was observing and measuring the X-ray spectra of various chemical elements using different crystals when he discovered that wavelengths and atomic numbers has a systematic relationship. He realized that the X-rays that were emitted from bombardment by cathode rays could be used as a characteristic of identification for different elements and their charge on the atomic nucleus. This discovery led to the reorganization of the periodic table of elements via the atomic number. From left to right the atomic numbers on the periodic table go up thanks to Henry Moseley.