In this view, it appears as if the electron does fall into the nucleus!īut it doesn't stay there! As you know, the potential energy of an electron becomes more negative as it moves toward the attractive field of the nucleus in fact, it approaches negative infinity. The per unit volume of space part is very important here as we consider radii closer to the nucleus, these volumes become very small, so the number of electrons per unit volume increases very rapidly. This is known as a probability density plot. This is confirmed by this plot which shows the quantity of electron charge per unit volume of space at various distances from the nucleus. Clearly, the electron is more likely to be found the closer we move toward the nucleus. If you had a magic camera that could take a sequence of pictures of the electron in the 1 s orbital of a hydrogen atom, and could combine the resulting dots in a single image, you would see something like this. The best we can do is specify the probability of its manifesting itself at any point in space. Quantum theory to the rescue!īy the 1920's, it became clear that a tiny object such as the electron cannot be treated as a classical particle having a definite position and velocity.
A revolving electron would transform the atom into a miniature radio station, the energy output of which would be at the cost of the potential energy of the electron according to classical mechanics, the electron would simply spiral into the nucleus and the atom would collapse. The proposal, first made in 1913, that the centrifugal force of the revolving electron just exactly balances the attractive force of the nucleus (in analogy with the centrifugal force of the moon in its orbit exactly counteracting the pull of the Earth's gravity) is a nice picture, but is simply untenable.Īn electron, unlike a planet or a satellite, is electrically charged, and it has been known since the mid-19th century that an electric charge that undergoes acceleration (changes velocity and direction) will emit electromagnetic radiation, losing energy in the process. The picture of electrons "orbiting" the nucleus like planets around the sun remains an enduring one, not only in popular images of the atom but also in the minds of many of us who know better.
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