Discovery of Subatomic Particles and the Bohr Atom

During the 50 years after the periodic tables of Mendeleev and Meyer were proposed, experimental advances came rapidly. Some of these discoveries are shown in Table 2-1. 

Parallel discoveries in atomic spectra showed that each element emits light of specific energies when excited by an electric discharge or heat. In 1885, Balmer showed that the energies of visible light emitted by the hydrogen atom are given by the equation 

1897 J. J. Thomson Showed that electrons have a negative charge, with charge/mass = 1.76 x lo C/kg 

1911 E. Rutherford Established the nuclear model of the atom (very small, heavy nucleus surrounded by mostly empty space) 

1913 H. G. J. Moseley Determined nuclear charges by X-ray emission, establishing atomic numbers as more fundamental than atomic masses 

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