Collapsing AtomsIn 1898 Henri Becquerel had discovered an entirely new physical phenomenon - radioactivity. This growth area in physics rapidly led to the realisation that atoms were not simply inert billiard balls. On the contrary, they have an internal structure. By the end of the first decade of the 20th Century sufficient research had accumulated for physicists to be able to begin making models of this structure. It was clear that atoms had a very small, dense, positively charged nucleus surrounded by negatively charged electrons. Ernest Rutherford proposed a planetary model for the atom - electrons in orbit around a nucleus like planets around a star. The fly in the ointment was electromagnetism. An electric charge moving in a circle emits energy. If electrons are classical particles emitting energy in this way, they would very rapidly dissipate all their energy and fall into the nucleus. A solution was offered by a young Danish physicist, Niels Bohr (see model and metaphor). The key was the abandonment of continuity in favour of quantisation. Bohr simply ruled out the possibility of electrons occupying every possible orbit. Instead they are confined to certain discrete energy levels. Although outlandish, his suggestion had the added attraction that it explained another anomaly - the fact that the light emitted by hot gases is emitted only at certain frequencies (spectral lines).
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Christopher Southgate |
