(1) Rutherford model faced some serious problems when subjected to the demands of electromagnetic theory. According to classical electromagnetic theory an accelerated charge particle must emit electromagnetic radiation. Now an electron moving in a circular orbit around the nucleus must experience centripetal acceleration and hence in accordance with the demands of electromagnetic radiation will lose energy in the form of electromagnetic radiation. This energy loss will come from the atomic system itself. As a consequence the electron will be continuously pulled towards the nucleus. Hence an electron can not remain in an orbit of radius r but moves along a spiral path as shown in figure.
As the electron goes nearer the nucleus, its speed increases continuously, the centripetal acceleration it experience also becomes more and it must emit more radiations. The net result of all this is that the electron crashes into nucleus after following a spiral path (in about 10-8 s). Hence Rutherford model cannot give us a stable atom.
(2) Since electron in orbit losses energy continuously the spectrum of the atom should be a continuous spectrum. However atoms exhibit a characterstic line spectrum. This fact is also ‘not in tune’ with the Rutherford model. However the idea of a planetary atom was hard to discard. Efforts were made to overcome this difficulty which was ultimately successfully explained by Neil Bohr in 1913.
However before Bohr’s published his theory a lot of experimental work was already available in the field of spectroscopy. It was established that emission of electromagnetic radiations in the form of spectral lines was the fundamental characterstics of the atoms. With the development in the experimental techniques, the wavelength of emitted spectral lines could be determined very accurately.
