" Z " was the number known as a physical characteristic of atoms after what year ?
Moseley was able to show that the frequencies of certain characteristic X-rays emitted from chemical elements are proportional to the square of a number which was close to the element 's atomic number ; a finding which supported van den Broek and Bohr 's model of the atom in which the atomic number is the same as the number of positive charges in the nucleus of the atom .