The concept of atomic numbers was developed by the British chemist Henry Moseley. In the early 20th century, Moseley conducted experiments that involved bombarding various elements with X-rays. By measuring the wavelengths of the X-rays emitted during these experiments, he discovered a pattern in the X-ray spectra that correlated with the atomic numbers of the elements.
Moseley's work demonstrated that the properties of elements were better organized by their atomic numbers (which correspond to the number of protons in an atom's nucleus) rather than their atomic masses. He arranged the elements in order of increasing atomic number and found that this arrangement aligned with other periodic trends, such as the periodicity of chemical properties.
Moseley's discovery of the relationship between X-ray spectra and atomic numbers played a crucial role in establishing the modern understanding of the periodic table and the organization of elements based on atomic number. Tragically, Moseley's promising scientific career was cut short when he was killed in action during World War I. However, his contributions to the understanding of atomic structure and the concept of atomic numbers continue to be recognized and appreciated.