Learn more physics!
Q:
Why doesn't the electron get sucked into the nucleus since the nucleus is positive and the electron is negative?
- matt (age 16)
mentor, oh, usa
A:
Matt -
That's a really great question!
The picture we often have of electrons as small objects circling a nucleus in well defined "orbits" is actually quite wrong. The positions of these electrons at any given time are not well-defined, but we CAN figure out the volume of space where we are likely to find a given electron if we do an experiment to look. For example, the electron in a hydrogen atom likes to occupy a spherical volume surrounding the proton. If you think of the proton as a grain of salt, then the electron is about equally likely to be found anywhere inside a ten foot radius sphere surrounding this grain, kind of like a cloud.
The weird thing about that cloud is that its spread in space is related to the spread of possible momenta (or velocities) of the electron. So here's the key point, which we won't pretend to explain here. The more squashed in the cloud gets, the more spread out the range of momenta has to get. That's called Heisenberg's uncertainty principle. Big momenta mean big kinetic energies. So the cloud can lower its potential energy by squishing in closer to the nucleus, but when it squishes in too far its kinetic energy goes up more than its potential energy goes down. So it settles at a happy medium, and that gives the cloud and thus the atom its size.
We've actually already answered a very similar question: try checking out
Why do Electrons Move? for some more details -Tamara
(published on 10/22/2007)
Follow-Up #1: Does the electron have a position?
Q:
But if we are saying that there is a probability of finding something here or there, this means that it must be somewhere at a definite place, it is just that we do not have the means to know without errors where is it. So if the position is definied but cant be determined, then how actually is the motion of the electron. I dont want to determine where it is, what is its momentum etc.
- Amol Bhave (age 16)
Jabalpur, Madhya Pradesh, India
A:
Your interpretation is what common sense would initially lead us to believe. However, we know that it isn't true. The electron is truly spread out. If these quantum variables (such as the electron position) that seem to be spread out had actual hidden values, then a set of experimental predictions known as the Bell Inequalities would be obeyed. In actual experiments the Bell Inequalities are consistently violated. Therefore the spread-out variables really are spread out.
The process of interacting with a large apparatus that's sensitive to where the electron is causes the formation of a state in which the electron's cloud has much less spread. This occurs via a quantum process called decoherence. There's no consensus about whether a single such state arises or a collection of states covering the whole range of possibilities.
Mike W.
(published on 12/05/11)
Follow-up on this answer.
