what stops electrons colapsing

Discussion in 'Physics & Math' started by Asguard, Jun 6, 2002.

  1. Asguard Kiss my dark side Valued Senior Member

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    Ok, surpringly enough this is inspired by a question TS asked

    i forget exacty what he asked but it got me thinking

    what stops electons sticking to the nucleus of an atom

    i mean i know they (mostly) can't just flote away but what puts them (and holds them) in orbit?
     
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  3. thed IT Gopher Registered Senior Member

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    Now this gets messy

    In classical physics the positive and negative charges of the protons and electrons should provide an attractive force causing the atom to collapse rapidly. Obviously they do not so what's going on?

    The basic tenet of Quantum Mechanics is that particles can behave as waves and that wave is interpreted to be a probability function. That is, it describes the probability of a particle being 'here' rather than 'there'. This wave is called Schroedingers Wave equation. It can be used, solved, in a variety of ways. The particular set of properties a particle has, and the associated wave, is better referred to as a state function and a particle is referred to as being in a given state or a superposition of states. What's interesting here is that the 'wave' equation also includes a term from matrix theory, the Hamiltonian, so you can solve Shroedingers Equation using matrix maths. Hence where the states come from in Quantum Mechanics and you can do tricks like 'rotate' the wave and find it's Jacobian.

    Any way, in an atom, the electric field generated by the particles acts as a 'potential well' constraining their behaviour. When you solve the Schroedinger wave equation for electrons in a potential well you find that they are only allowed to take unique values (they are quantised) for spin, angular momentum and energy. Fiddle around a little more and you find that no two electrons are allowed to have the exact same 'state functions'. This is Einstein-Fermi statistics and why electrons are called Fermions. Fiddle around a little more and you plot the positions of the electrons. You find that they exist in clouds rather than distinct orbits.

    In short, the state function (toal energy)of the electron determines it's position in the atom. If the electron gains enough energy it can escape the potential well it is in.

    For what it's worth, you can only solve this exactly for the Hydrogen atom. Anything more complex requires you to make approximations.

    So, it's a quantum mechanical effect that keeps the electron bound to the nucleus.

    Is that clear? No! Don't worry, it takes some understanding. I always understood it best after copious amounts of alcohol. Problem is no one could read my handwriting afterwards

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  5. thed IT Gopher Registered Senior Member

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  7. Asguard Kiss my dark side Valued Senior Member

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    i only did physics to year 12, not university level so my grasp is rather basic

    i rember hearing somewhere that the conventional drawing for the atom was wrong and that they don't really orbit like that

    so is what your saying that they don't stick because they are to excited? or because the positive field is general?

    sorry alot of the higher physics goes over my head even if it IS interesting
     
  8. Asguard Kiss my dark side Valued Senior Member

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    23,049
    AH

    thank you

    that third link was very helpfull
     
  9. James R Just this guy, you know? Staff Member

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    Here's a shorter answer:

    The positive and negative charges on protons and neutrons attract the electrons to the nucleus. According to classical physics, electrons in orbit around the nucleus should radiate their orbital energy away quickly and fall into the nucleus.

    Quantum physics explains why this doesn't happen. Energy levels of electrons in atoms can only take specific values. The Pauli exclusion principle states that no two electrons can be in the same quantum state at the same time. Together, those principles account for the complicated electron configurations of atoms, and also explain why electrons don't spiral into the nucleus.
     
  10. Joeman Eviiiiiiiil Clown Registered Senior Member

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    Set the temperature to absolute zero. That should do it

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  11. Mr. G reality.sys Valued Senior Member

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    Lack of the need: abhorance of destructive interference.
     
  12. huh??? Registered Senior Member

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    According to dirac, virtual photons. According to casimir, zero-point energy. Same thing.

    By the way, electrons are considered fermions because they have mass. I believe every fermion is subject to pauli's exclusion principle, but I forgot.

    <I>Quantum physics explains why this doesn't happen. Energy levels of electrons in atoms can only take specific values. The Pauli
    exclusion principle states that no two electrons can be in the same quantum state at the same time. Together, those principles
    account for the complicated electron configurations of atoms, and also explain why electrons don't spiral into the nucleus.
    </I>

    Except that that isn't always true, only when an atom is at ground state. When they are slightly excited, it is the casimir effect that keeps them from colapsing.

    <I>Set the temperature to absolute zero. That should do it
    </I>

    Uh, no, because even if 0&deg;K was attainable, energy can never be "0", so you could never take all the energy away, even if you take away billions of jouls, there will still be some left. That's ZPE.
     
  13. James R Just this guy, you know? Staff Member

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    huh? :

    <i>By the way, electrons are considered fermions because they have mass.</i>

    Grab a physics dictionary and look up "fermion". The definition of what a fermion is has nothing to do with mass. A fermion is any particle with half-integer spin. All fermions are subject to the exclusion principle.

    <i>Except that that isn't always true, only when an atom is at ground state. When they are slightly excited, it is the casimir effect that keeps them from colapsing.</i>

    That's the first time I've heard that. Can you explain how the Casimir effect keeps them from collapsing?
     
  14. Prosoothus Registered Senior Member

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    thed,

    Based on your response, it appears that the electrostatic interaction between protons and electrons is not always attractive. If what you said is true, shouldn't the four fundamental interactions be revised to explain these types of subatomic interactions as well as interactions at a large scale?

    About a year ago, someone on Sciforums suggested that the electric charge of an electron may be oscillating instead of being constant. I was wondering if by assuming that the charge of protons and electrons oscillate, a model can be developed that would explain the stability of atoms using only the electrostatic interaction.
     
  15. temur man of no words Registered Senior Member

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    You can think that (ground state) electron is already collapsed and stuck to the nucleus, but in quantum mechanical sense. The closest thing you get to sticking to the nucleus in quantum mechanics is the ground state.
     
  16. AlphaNumeric Fully ionized Registered Senior Member

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    You can calculate the ZPE (I prefer 'Vacuum energy') for such things as a Hydrogen atom or a simple harmonic oscillator and it's not infinite. Only in field theory do you get that.

    For instance, if \(E_{0}\) is the ground state in a SHO and \(E_{1}\) the first excited state then the difference between 0 energy and the ground state \(E_{0}\) is \(\frac{1}{2}(E_{1}-E_{0})\). Hardly 'billions of joules'.

    The electron orbitals are time independent solutions to the Schrodinger equation. The Casamir effect only occurs in field theory, yet non-relativistic QM explain electron orbitals without field theory's input.
     
  17. Walter L. Wagner Cosmic Truth Seeker Valued Senior Member

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    Another way of visualizing it is to recognize that the electron is not a 'particle' per se, but a wave function [as per Schroedinger]. The lowest ['ground'] state for that wave function, constrained by a positive charge, is a standing wave which corresponds with the lowest energy orbital for the 'electron'. The other 'standing waves' at higher energies [more than one proton, producing more than one standing wave for several electrons] take more elaborate form, producing various electron-shell sharing capabilities, useful for understanding chemical binding. Lots of good inorganic chemistry texts depict those 'standing wave' functions in graphic representation.
     
  18. visceral_instinct Monkey see, monkey denigrate Valued Senior Member

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    I've always wanted to know that, but never had the guts to ask. Thanks Azzy.
     

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