Why don't electrons fall towards the nucleus?

Question

I remember my teacher saying the flaw with Rutherford's model was that it doesn't explain why atoms do not fall towards the center of an atom. Why don't they fall towards the center? I guess this may fall into "Why doesn't the earth fall towards the sun". This may be a common sense questions, but no one has ever given me a straight answer about it before...

Answer 1

This isn't going to be a straight answer either but I hope it at least points you in the right direction.

For one thing, it is not the same reason that the earth doesn't fall into the sun. That can be described by classical physics for objects in circular motion. To begin with, electrons don't go around the nucleus in a circle at all (or even an ellipse). They move through what is called an "orbital" (a key point, it is not in orbit but in an orbital. If you want to see what orbitals are thought to look like check wikipedia for "atomic orbital", it has some good images) which can only tell where an electron is likely to be at any one point. It is impossible to determine where an electron is at any one time (for a few reasons). In fact the only places it cannot be is on the nucleus itself or some infinite distance away from the nucleus. All of this is part of quantum mechanics, which is extremely complicated (but interesting) and if you'd like to learn more I suggest you take a class on it in college.

To be perfectly honest, I have yet to take one of these courses myself (although I plan to) so I'm not completely sure of the reason but I believe it has something to do with the electron itself having energy. I know that the reason the nucleus does not blow apart is because of something called the strong nuclear force, which has to do with interactions between quarks and gluons. A gluon is the messenger particle for the strong nuclear force (the strong nuclear force equivalent of a photon), which is named because it is the "glue" that holds the nucleus together.

Answer 2

For the same reason that the Earth does not fall toward the sun and the moon does not fall toward the Earth.

The laws of motion tell us an object will remain in the same straight-line motion unless it is acted upon by an outside force. The electrons are moving VERY FAST. The nuclear charge is an outside force that acts on the electrons. When you combine the straight-line path of the electron and the downward pull of the nuclear charge you get an "arc" or projectile motion path.

In essence the electron is constantly being pulled toward the nucleus, but the electron is moving so fast that as it falls toward the nucleus its curved path makes it just miss hitting the nucleus. It keeps falling, but missing the nucleus. This gives the orbit around the nucleus.

The Earth does not fall toward the sun for the same reason. The speed of the Earth in a straight-line combines with the gravitational pull of the sun toward the center to give a curved path. The Earth is always falling toward the sun, but the speed at which the Earth travels makes it move so fast that it misses the sun as it falls around the sun. An orbit of anything works on the same principles. Objects are always falling toward the body they orbit, but they travel so fast that they move away and around the body instead of crashing into it.

Answer 3

The speed at which the electrons are travelling is so great, that it keeps them in their "orbits" (electron shells), avoiding crashing into the nucleus.