Editing Atomic number (section)

=== The Rutherford-Bohr model and van den Broek ===

[[Image:Bohr atom model.svg|thumb|right|300px|The Rutherford–Bohr model of the [[hydrogen atom]] ({{nowrap|''Z'' {{=}} 1}}) or a hydrogen-like ion ({{nowrap|1=''Z'' > 1}}). In this model, it is an essential feature that the photon energy (or frequency) of the electromagnetic radiation emitted (shown) when an electron jumps from one orbital to another be proportional to the mathematical square of atomic charge ({{nowrap|''Z<sup>2</sup>''}}). Experimental measurements by [[Henry Moseley]] of this radiation for many elements (from {{nowrap|''Z'' {{=}} 13 to 92}}) showed the results as predicted by Bohr. Both the concept of atomic number and the Bohr model were thereby given scientific credence.]]

In 1911, [[Ernest Rutherford]] gave a [[Rutherford model|model]] of the atom in which a central nucleus held most of the atom's mass and a positive charge which, in units of the electron's charge, was to be approximately equal to half of the atom's atomic weight, expressed in numbers of hydrogen atoms. This central charge would thus be approximately half the atomic weight (though it was almost 25% different from the atomic number of gold {{nowrap|1=(''Z'' = 79}}, {{nowrap|1=''A'' = 197}}), the single element from which Rutherford made his guess). Nevertheless, in spite of Rutherford's estimation that gold had a central charge of about 100 (but was element {{nowrap|1=''Z'' = 79}} on the periodic table), a month after Rutherford's paper appeared, [[Antonius van den Broek]] first formally suggested that the central charge and number of electrons in an atom were ''exactly'' equal to its place in the periodic table (also known as element number, atomic number, and symbolized ''Z''). This eventually proved to be the case.