ABSTRACT
The response to Rutherford's work was the so-called planetary model of the atom – electrons revolving around the massive small nucleus like planets around the sun. The implications of this model are manifold and require explanation. The planetary model clearly yields zero net charge for the atom and, by having a well-defined nucleus, also explains Rutherford's data on alpha particle scattering. It also opened a can of conceptual worms that could not be dealt with by the physics of the time. The radii and the energies of electrons in a Bohr atom can be presented in a somewhat different format from the two preceding figures. The innermost electrons of a heavy atom are held to the nucleus much more tightly than the electron of hydrogen because the polyelectronic atom's nucleus has a large positive charge. Ionization provides us with one consideration not associated with excitation: absorbed energy in excess of the ionization energy can be partitioned into electron kinetic energy.
