is the atomic number, which coincides, as suggested by the Dutch
scientist Antonius Van den Broek, with the magnitude of the positive
charge on the nucleus of the atom, became the basis for classification
of chemical elements. In
1920 the English physicist James Chadwick experimentally determined
the nuclear charge of copper silver and platinum, obtaining for them
the values of 29.3, 46.3 and 77.4, respectively, which almost
coincided with their atomic numbers 29, 47 and 78.