In 1913 the English scientist, Henry Moseley (1887-1915), determined the atomic number of each of the elements and modified the 'Periodic Law' accordingly. Moseley realised that when atoms were arranged according to increasing atomic number, the few problems with the periodic table which had been developed by Dimitri Mendeleev disappeared. Because of Henry Moseley's work, the modern periodic table is based on the atomic numbers of the elements.
Courtney, debate?