We explained away doubts about the stability of Rutherford’s nuclear atom by stating, simply, that the electron must orbit the nucleus like the moon about Earth. We confess now to telling you only half the story. By setting the electron in motion about the nucleus, we actually doomed it to an even grimmer fate.
The moon is a poor model of the electron, not only because the electron is so much smaller, but because unlike the moon, an electron has an electric charge. You recall that any time a charged particle changes speed or direction (i.e., accelerates), it emits electromagnetic radiation. This was the basis for the light emitted from our heated fireplace poker as well as the radio waves in Hertz’s lab.
An electron in orbit about a nucleus will be constantly changing direction in order to stay on its circular path. This means that it will be constantly accelerating which, of course, means that it will be constantly radiating. However, energy must be conserved, so as it radiates, its velocity will slow. As it slows down, it will begin falling into the nucleus. In no time at all, the electron will have spiraled haplessly into the positively charged nucleus never to be seen again. The atom will have collapsed.
Maxwell’s classical theory allows us to calculate just how long this will take: just about 1 × 10-12 seconds. The fact that you’re still sitting there, and that your atoms have yet to collapse, should convince you that Rutherford’s model for the atom was missing a little something.
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