Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Charge attraction inside an atom

  1. Oct 5, 2011 #1
    If the electrons in an atom are negatively charged, and the nucleus is positively charged, what keeps them from coming together? I know that the old model of an atom as a tiny solar system is long obsolete, but still, there is supposed to be some discrete space between the electron structure (whatever it may conceived to be) and the nucleus. How come they don't collapse together attracting each another?
  2. jcsd
  3. Oct 5, 2011 #2


    User Avatar
    Science Advisor

    Frequently Asked Question #37! :smile: They do come together. An electron in an S orbital (L = 0) has a nonzero probability of being at the origin. Crudely speaking that means it spends part of its time inside the nucleus. Normally it just passes through and continues on its way, but that's just because of energy considerations.

    In a hydrogen atom, for example, you might think that the electron and proton might coalesce and form a neutron. But the neutron's mass is greater than electron and proton put together, so for that reason it just can't happen. For certain other nuclei, however, a reaction is energetically possible, and does happen. This is called 'electron capture' or 'K capture'. See the "Electron capture" page on Wikipedia for examples.
  4. Oct 5, 2011 #3
    Yeah, once atoms was described as small 'Solar systems', and the reason why they didn't fall into the nucleus was their angular momentum. Ernest Rutherford explained is as 'their velocity is sufficient to exactly balance the attraction exerted, and so they maintain orbits.'

    Today the view is different. Instead of 'particles' per se you have a 'probability cloud' 'orbitaling' instead, not orbiting as a planet does. The 'orbitals' are defined from their quantization, or 'energy', that comes in certain defined values. That one comes from Max Planck and Albert Einstein (black body radiation and photoelectric effect).

    Niels Bohr was the guy first suggesting that it was this phenomena that made them stay in place, and so the idea of pinpointing a 'electron' became very tricky in that Heisenberg's uncertainty principle doesn't allow you to fixate all properties of it.

    The closer you define it to some specific space (position) the more uncertain it momentum (velocity, sort of) becomes, and so it behaves more as a 'cloud' than as a particle. You can squeeze the cloud 'smaller', but then its momentum goes up and so it becomes uncertain again.

    Now you might wonder the same as I do. If it is a fault created by us measuring, interfering with its former state, creating this? Or if it is a principle more resembling some 'constant', just as 'c' that never change its invariant speed in a vacuum (locally), no matter what speed I find myself to have relative some third party as I measure that speed. That is, if it is some sort of 'border' for SpaceTime. I think it's a QM 'border', but I can't define how it really works.

    And that's the model we use today, as I understand it. Then you also have 'forces' acting between those particles building a atom too, photons, pions, gluons etc, that act as 'force carriers', as well as 'quarks' that are some smallest 'building blocks'.

    Maybe a 'electron' is more of a bubble created by the 'forces' acting on it, than really there?
    :) maybe..
    Last edited: Oct 5, 2011
  5. Oct 5, 2011 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Please start by reading the FAQ subforum in the General Physics forum.

  6. Oct 5, 2011 #5
    Nice one.
    What happens when a different angular orbit is considered with just one electron in it? In this case, the node (pt of min probability) is coincident with the core, would you conjecture that the electron can overcome the mass of the core, penetrate it and then escape it? Or, is the electron trapped within the 1/2 space of the orbit (probability cloud)?
  7. Oct 5, 2011 #6
    Mathew, I think you want a roadmap that is classical there? A causality chain that we can follow. QM doesn't really fit such a map, or maybe it is me that can't see it? When I think of QM it's indeterminacy that I see first, causality chains after. We use statistics to define what's probable there, and all statistics must build on histories, at least as I know? Can you use statistics without having a history to build it on? I'm not sure there?

    The really surprising thing is that statistics works as well at a QM scale as macroscopically, or maybe it's not surprising at all thinking of it :)
  8. Oct 6, 2011 #7
    Ah, yes.

    And you find them sufficient?

    Statistics is always about histories, isn't it? Or could you use it on something never seen in our universe, a universe where things don't follow our definitions and constants? That's one thing I'm wondering about. If it is so that you need a 'history' first to define a probability, then statistics always will be one of the strongest tools there is, and probably also one of the most accurate.

    Are there principles in statistics that we can use on that universe too, or would we have to build a 'history' to define the probability? Weird thing to wonder, but it got on my mind.
  9. Oct 6, 2011 #8
    one of your quotes didnt take
  10. Oct 9, 2011 #9
    My two scence lol; In agreement with yoron I believe the carriers together act as a tensor represented in a multi-functional array of numerical values that carry an equal opposite attraction. However; I may be wrong. Someone please correct if so.
  11. Oct 9, 2011 #10


    User Avatar
    Homework Helper
    Gold Member

    The important thing here is to understand how quantum physics change our whole understanding regarding what particle is and what it does.

    The old classical understanding where a particle is a small ball of localized mass that has a definite orbit which is affected by the forces acting on it via newton's 2nd law F=ma is simply wrong or inadequate in quantum physics. In quantum physics a particle though it might still be some localized mass it is viewed as a particle-wave, it does NOT have a definite orbit, it rather has an orbital which is defined by the particle's wave function which in turn is affected by the total energy the particle has. Schrodinger's wave equation plays the role that F=ma plays in classical particles.

    So a question like why the electron doesnt spiral into the nucleus is kind of "invalid" question for quantum physics. Electrons simply cant have a definite spiral orbit neither any kind of classical orbit. Electrons can only have orbitals and wave functions, a valid question for quantum physics would be why the electron's wave function has a minimum or a maximum at the point where the nucleus is.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook