In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore resequenced the table by nuclear charge rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
Henry Moseley's discovery of the pattern of nuclear charge (the number of protons in the nucleus).
He discovered that each element has its own atomic number.In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore resequenced the table by nuclear charge rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
Researching around I would say discovery of the "atomic number" used for ordering the elements in the periodic table would probably be the answer. This is recorded as being in 1913.
Modern periodic table is invented by Henry Moseley.
Henry moseley
Henry Moseley in 1914
not much
Henry Moseley discovered a relation between the atomic number and the X-ray wavelength of a given chemical element; this was a physical confirmation of the periodic table and the order of elements in the table.
Henry Moseley sorted the chemical elements on the Periodic Table in order by their atomic numbers. Moseley was a British chemist who had studied under Rutherford.
Henry Moseley
In 1914 Henry Moseley found a relationship between an element's X-ray wavelength and its atomic number (Z), and therefore rearranged the table by nuclear charge / atomic number rather than atomic weight. Before this discovery, atomic numbers were just sequential numbers based on an element's atomic weight. Moseley's discovery showed that atomic numbers had an experimentally measurable basis.
In 1912, Henry Moseley, an English physicist showed that periodicity was a fucntion of the atomic number rather than of atomic mass. Our present periodic tables are now constructed using atomic number as the basis of arranging the elements and the periodic law being stated as, the physical and chemical properties of the element are periodic functions of their atomic numbers. This periodic recurrence of properties is emphasized by arranging the elements in a table such that elements with similar properties are aligned in a vertical column. This arrangement is called the Periodic Table.