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Which force seperates the electrons and nucleus and causes the electrons to orbit?

  1. Apr 3, 2005 #1
    which force seperates the electrons and nucleus and causes the electrons to orbit???

    a freind told me that the size of the electron means that the nuclei cannot absorb it, but i am still confused and not sure if he knew what i meant in my question.
  2. jcsd
  3. Apr 3, 2005 #2


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    The same reason why the Moon does not fall on Earth: kinetic energy!
  4. Apr 3, 2005 #3


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    That's sort of partly true, but not exactly. Really, the properties that will tell you whether an orbiting object will crash into that which it's orbiting are both the angular momentum and energy. The moon could have the same kinetic energy and distance, but still crash into the earth if its angular momentum were small. These arguments don't really apply to electrons around nuclei, though, so I don't think it answers the OP's question.

    The most straightforward answer to the question is that the electrostatic force keeps the electron bound to the nucleus. Is that what you're looking for, hexhunter?
  5. Apr 3, 2005 #4
    i understand that EM stops it from running away, but as the nucleus is +ve and the electron -ve, there is no possibility in my mind that the wouldn't just sink straight into the nucleus, unless if it is just chance that when the nuclei and electrons met, that the electrons where quickly enough forced into the neuclei at their conceivment to make orbit around the nucleus without the EM being too powerful for the electrons to avoid.

    though any theory like this would surely suggest that all atoms will neutralise, or do whatever is meant to happen in this event, like a time bomb, not like any of the other 'end of the universe' theories that i have heard of...
  6. Apr 3, 2005 #5


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    Remember that at the quantum level, there's no friction, gravity, air resitance, etc. to impede it's momentum. Also, it can only reduce it's orbit in discrete steps. In order to move closer to the nucleus, the electron has to spit out a photon to drop into the next energy state (orbital).
  7. Apr 3, 2005 #6
    What your friend was probably talking about was that the nulceus is too small to contain an electron from a quantum perspective.

    A nucleus is an extremely tiny thing (diameter aprox 10^18cm), and if there was an electron inside it then we would know its location almost exactly. According to the uncertainty principle, the electron would then have a very large (but uncertain) kinetic energy, which would cause it to break out of the nucleus. So electrons reach a compromise, depending on their energy they orbit the nucleus in shells of "surface area" dictated by this rule.
  8. Apr 3, 2005 #7
    here is what you sound like:

    "i understand that gravity holds the earth to the sun, but since gravity is attractive, there is no possibility in my mind that the earth wouldn't just sink straight in to the sun".

    Think of swinging a pail above your head. The pail is orbitting you, and you are holding it by a rope. The only force you exert on the pail to make it orbit you, is pulling the rope in towards yourself!
  9. Apr 3, 2005 #8
    so the Kinetic energy of the electron is enough to avoid the EM attraction, but keep the orbit, and the electron will never slow, because of the vacuum? but while there is no gravity, there still is the EM from the interaction between the charges.

    also, is the orbit round???
  10. Apr 3, 2005 #9
    acording, are you talking about the electrons in the s, p, d, or f orbits
    The ones in the s orbit are spherical
    the p are kinda dumbell shaped
    the d are two dumbell crossing at X,Y,or Z axis besides the d5 (5 should be subsized) which is a dumbell with a ring aroud it :confused: (that is what the text book showed)
    the f are for the most part 3 dumbell, but there are some weird ones as well
  11. Apr 3, 2005 #10
    that's it!

    however one difficulty in this is that it is sometimes hard to understand how the uncertaincy principle can force an electron to behave in this or that way...
  12. Apr 3, 2005 #11


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    Alright, there seem to be two points of confusion here, one classical and one quantum. If we could treat atoms as mini solar systems then Crosson's explanation would end the story. That is, the electron would be pulled inwards by the attraction of the proton, but by Newton's first law, its momentum would want to keep carrying it in some other direction. Some balance would be achieved between these two effects that would allow the electron to continue in an orbit around the nucleus, just as happens with the planets around the sun.

    However, this is not a good description of atoms. It turns out that, at these scales, the laws of quantum mechanics begin to become apparent and the electron begins to behave in ways that make no sense in the description I gave above. For this, locke gave a good answer. The electron cannot be treated as a simple object with definite position and momentum, but instead as a sort of probability wave that can exist in a series of states. These were partially described by lawtonfogle.
  13. Apr 3, 2005 #12


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    Yeah. I learned to consider the area around the nucleus as an electron orbital cloud. A haze of varying probabilities, and somewhere in that cloud the probability of an electron being there is high enough that it really is.
  14. Apr 3, 2005 #13


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    Keep in mind that the "cloud" and the probability distribution function are one and the same. Your description is a sort of semi-classical way of thinking about it, but I think the Copenhagen interpretation implies that the probability "cloud" is the most fundamental physical reality.
  15. Apr 3, 2005 #14


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    Yeah, that's what I meant. Bad choice of phrasing on my part. I'm used to dealing with people who have no knowledge of science whatsoever, so I sometimes translate sloppily.
  16. Aug 10, 2011 #15
    Re: which force seperates the electrons and nucleus and causes the electrons to orbit

    Correct me if I sound dumb, but the 'most fundamental physical reality' is uncertainty?
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