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Why would the atoms collapse?

  1. Sep 6, 2003 #1
    I've heard many times that one of the major faults of the classical model of an atom is that it would collapse. In other words, the electrons wouldn't stay orbiting the nucleus for very long before they hit into it.
    Although I've heard this many times, I don't think Ive ever heard the reason why. Anyone mind explaining this for me?
  2. jcsd
  3. Sep 6, 2003 #2


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    According to Maxwell's equations, anytime a charged particle accelerates it emits electromagnetic radiation.

    In order to stay in orbit, an electron must always be accelerating (because its direction is ever-changing). Thus, the electron is always emitting electromagnetic energy.

    Because the radiated energy keeps going up, some other sort of energy must keep going down. The only candidates I can imagine are electric potential energy and kinetic energy, and a continual decrease in either would cause the electron to fall into the nucleus.
  4. Sep 8, 2003 #3
    Hi Rocky,
    Hurkyl said it correctly. The QED people refer to a stable quantum orbital as a "standing-wave" which means it is not radiating which implies that any radiation from the orbital would deminish the required energy at which time the electrons would fall into the nucleus. Cheers, Jim
  5. Sep 9, 2003 #4
    Honestly that alone doesn't seem to be enough to rule out the orbiting hypothesis. Seems to me that at the atomic scale there could be so many possible complex mechanisms for keeping an electron in orbit. For example, an orbiting electron would cause the nucleus to vibrate (accelerate), couldn't the EM radiation from the accelerating nucleus possibly work with the oribiting electron to keep it in oribit? I must say that I havn't actually diagramed that thought out to see how much sense it makes. But To make a point, it just seems like there could be endless possibilities like that one that could enable the orbiting hypothesis to stand.
    Also Hurkly, if we consider an electron in an atom to be in motion, doesn't it need to accelerate in some manner to stay around the nuclues. So Wouldn't it have to radiate EM and lose energy no matter what? How is this explained these days?

    I can't really picture an electron as a "standing wave". Plus I don't see how an electron being a "standing wave" would prevent it from radiating EM. Maybe you could clarify?

    Wish I had the self control to wait till morning to post this, but I don't. Im tired, so excuse if it seems rambling. Thanks,Goodnight![zz)]
  6. Sep 9, 2003 #5
    Why should it? What forces are acting on the nucleus, from the electron, to make it vibrate. For vibration you need to increase kinetic energy, that would come from the electron so it looses energy and falls. Bear in mind the nucleus is hugely more massive than the electron as well. Plus the only forces are EM forces and these want to push the electron away.

    Any 'mechanism' you invent has to get around those problems.

    That would break conservation of energy, as above.

    The hardest thing to realise in QM is that waves and particles are the same thing. An electron acts as a wave so can form a standing wave. It actually goes through the nucleus as well.
  7. Sep 9, 2003 #6


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    So, why don't free electons run into the nucleus? What is the probabliity that a few manage to get through?
  8. Sep 9, 2003 #7
    Different situation. The electrons caught inside the potential well of an atom obey one set of probability functions, the standing waves if you will. Those outside obey a different set and will be repelled by the potential difference between the nucleus and electron.

    There is a small, but finite chance, the electron could tunnel through but it is very unlikely.
  9. Sep 9, 2003 #8
    Non radiant quantum orbital!

    Hi again Rocky,
    Sorry I confused you. The "standing wave" is not my model but that label is a patch that the QED people use because with them the whole monte involves only electricity and therefore only waves. The real model explaining the non radiating aspect of each quantum orbital is in the loop behavior. Knowledge of vector cross products is quite valuable here since it tells why there is a magnetic dipole perpendicular to the plane of the looping charge and alone it is strong enough to radiate aplenty. However, remember that the charge on each electron is intrinsicly welded to a unit mass which is also looping and which forms a cross product dipole called torque that exactly counters the magnetic dipole. Nature is so very clever, don't you think? Cheers, Jim
  10. Sep 9, 2003 #9
    quantum electrons never penetrate the nucleus!

    Hi Thed,
    Not just unlikely but impossible. The only way a quantum electron interacts with the nucleus is not a "penetration" but a so-called k-capture whereby only the weakest 1s electron nearest the nucleus is captured; particularly if the nucleus is proton rich isotope.
    I'm reminded of pictures in a chemistry text which showed balloons that represented the probability of the position of a non coupled valence electron. My students imagined that the two balloons 180 degrees apart and pointed to the nucleus somehow meant that the electron traveled at high speed from balloon to balloon and through the nucleus many times. My students were wrong. It is for these uncoupled electrons that the Heisinberg UP is indicated pictorially. Cheers, Jim
  11. Sep 9, 2003 #10
    Hey Neo,
    Thanks for clearing up the standing waves bit.

    Now I'm gana need a bit of help with this. By this it sounds like we're back where we started. I can't imagine any possible electron loop where there is no acceleration thus no radiation. So how is the radiation prevented?
  12. Sep 9, 2003 #11
    Most quantum orbitals become "dark Matter"

    Hi Rocky,
    The thing to remember is that the slightest iota of radiation comes at the expense of the natural stability of the quantum orbital; IOW if the electrons slow down they no longer possess the kinetic energy that that particular quantum orbital is designed to require. Of course the valence electrons in a stable molecule are in quantum orbitals that are called molecular bonds that are easily broken. With sufficient excitation, quantum electrons can be removed from their stable residence in their atomic kernel. In general though, it is very difficult to destroy an atom e.g., when I have a nose bleed the iron, when the hemoglobin finally decomoses, remains as an iron atom that does not decompose but may become rust and so forth; finally it becomes Dark Matter. Cheers, Jim
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