Moseley contribution was; the atomic number should be the organizing principle for the periodic table. Mosely worked on Mendeleev's periodic table to try to correct some disadvantages of Mendeleev's table. Mendeleev arranged the elements in his table according to their atomic masses, not atomic numbers which made some disturbances at his table. Moosely arranged the elements according to their atomic number, not an atomic mass; an important step that helps in the building of the modern periodic table.
