Speedy Electron
Most recent answer: 10/22/2007
- Dana Bahr (age 49)
Sch Dist 885, Albertville,MN,US
Hi Dana,
That�s a great question, and the answer may surprise you.
The picture we often have of electrons as small objects circling a nucleus in well defined "orbits" is actually quite wrong. The electrons really aren't at any particular place. However, we CAN figure out the volume of space where we are likely to find a given electron if we look, since that "measurement" somehow causes the electron to be found in a small region. 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 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 for some more details -Tamara
(published on 10/22/2007)
Follow-Up #1: Electron around a nucleus
- Brian Matt
American Gnostic sch, Yelm, WA
The picture we sometimes see of electrons making orderly circular orbits around a nucleus (like little planets in a micro solar system) is clearly wrong, nevertheless it helps picture part of what is going on. We know the electron and the nucleus are attracted to each other by the electromagnetic force, and are somehow "bound together" (just like the earth and the moon are).
The thing that is a little harder to visualize is the way the electron "orbits" the nucleus. The mathematics of quantum mechanics, (which allows us to study atoms the same way that Newtons F=ma allows us to study big objects), tells us that the electron is more like a cloud that surrounds the nucleus. In other words, the position of the electron is not at all well defined (like a little planet) but rather it is smeared out over a large volume all around the nucleus. Picture the nucleus as a tiny grain of sand that lives at the middle of a puff of smoke, which is the electron.
The shape of the electron "cloud" or "smoke" depends on how many other electrons are caught by the nucleus, how much energy the electron has, and other more subtle things as well. Sometimes the cloud will be spherical, sometimes it will be shaped like a doughnut, sometimes like a dumbbell etc.
If you look in a high-school chemistry book, or a college level modern-physics book you can find out more.
MS
(published on 10/22/2007)
Follow-Up #2: Between the nucleus and an electron?
- Narmeen (age 16)
London
Mike W.
(published on 10/22/2007)
Follow-Up #3: quantum peculiarity
- Noel Khan (age 31)
Victorville, CA
point one: Yes, to be more precise what's left is a new cloud, more localized than the first one. Good point.
point two. Once again I wrote a little sloppily. The only way the cloud can squish in more is if something does work to squeeze it in. Otherwise, as you say, energy wouldn't be conserved.
point three: No, in the simple case of low-energy hydrogen the cloud isn't spinning at all. (Higher energy states can spin.) The kinetic energy term actually comes from the range of possible radial velocities implicit in the electronic state. However, this cloud is not changing in time. Imagine a classical standing wave, say on a string. The wave is a mixture of waves traveling left and right but overall does not move. The electron wave is a little similar, but in 3-d. I know this sounds very mysterious.
point 4: Electromagnetic waves are a subset of electromagnetic fields, just ones that actually carry energy around. There's energy in the static field from a charge, but it isn't going anywhere.
I hope this helps.
Mike W.
(published on 10/08/2009)
Follow-Up #4: How long does an electron orbit take?
- r.s. (age 48)
Canada
You could make an electron state that looks more like a small blob actually orbiting the nucleus, but it would have to be a combination of states with different energies and those energies would have to be near the value at which the electron would escape from the nucleus. The time that packet would take to make an orbit would depend on what ingredient single-energy states went into it. There's no maximum time, but the minimum time would be about 10-14 seconds. If you'd settle for a big blob that doesn't quite resemble an orbiting object but does rotate around the atom, the minimum rotation time is about 4.055*10-16 s for a hydrogen atom. That would be a combination of 1s and 2p states.
Mike W.
p.s. Those orbits won't last very long, since they radiate electromagnetic energy in about a billionth of a second.
(published on 02/11/2011)