• The scientist who first of all, showed that the atomic number is a more fundamental property of an element than its atomic mass was Henry Moseley. He declared this concept in the Year, 1913. He is best known for the Moseley’s Law and contributions to Physics. Moseley is also associated with the publication of the very first Long Form or Modern periodic table that is used to date.
• Moseley performed experiments and studied the frequencies of the rays emitted from the elements. With these experiments, he concluded that the atomic number is a more fundamental property of an element than its atomic mass.
• The atomic number is a more fundamental property of an element than its atomic mass. On arranging elements in the increasing order of their atomic numbers, similarities appear in physical and chemical properties at regular intervals.

Source: NCERT