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

What happens when electrons crash into their proton

  1. Apr 2, 2009 #1
    Do they just destroy each other?
     
  2. jcsd
  3. Apr 2, 2009 #2

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    No, this doesn't actually happen. Electrons are often thought of orbiting a nucleus containing protons like planets orbit the sun. But this is not an accurate picture - that model does not account for observed results (or even close). In reality, electrons do not move to the proton (i.e. into the nucleus) as expected. Even though there is an attraction, there are also limits.

    Things like the Pauli Exclusion Principle, the Schrödinger Equation and other elements of quantum mechanics yield different solutions than you would guess off hand. I would recommend that you google the subject and read up more. Then ask some questions based on that.

    For example, look at the PhysicsForums FAQ, 2nd item:

    WHY DON’T ELECTRONS CRASH INTO THE NUCLEUS IN ATOMS?

    Contributed by Marlon and edited by ZapperZ

    If one describes atoms using only the Coulomb forces, the electron and the nucleus will attract each other and no stable atoms could exist. Obviously this is not the case. Niels Bohr was the first (1913) to propose a better model, which consisted of electrons moving around the nucleus in circular orbits. Each orbit corresponds to a certain discrete energy level. This model is based upon the quantisation of the angular momentum.

    Unfortunately, electrons moving in a circular orbit have an acceleration due to the centripetal force. In classical electromagnetic theory, an accelerated charged particle must emit EM-radiation due to energy conservation. Hence, the electron would lose energy and spiral down towards the nucleus. Again stable atoms could not exist. What is wrong now?

    It turns out that the picture of electrons moving in circular orbits around the nucleus isn’t correct either(*). The solution here is the implementation of Quantum Mechanics via the Schrödinger Equation and the concept of wavefunction. By applying such formalism, the “electron” occupies a volume of space simultaneously, so that it is “smeared” in a particular geometry around the nucleus. While there are no more “orbits”, we do use the term “orbitals” to indicate the shape of such geometry. However, this term should not be confused to mean an orbiting electron similar to our planets in the solar system. By describing the system in terms of the QM wavefunction, it creates stable states for the nucleus+electrons system that matches very well with experimental observation of standard atomic spectra.

    Since there are no more “orbits” in the conventional sense, the problem of electrons radiating due to an accelerated motion is no longer meaningful. It explains why we have stable atoms.

    To read more in detail: http://scienceworld.wolfram.com/phys...rogenAtom.html [Broken]


    (*) By saying that “an electron orbits the nucleus”, one is already implicitly assuming that one can track the position and momentum of that electron in an atom over a period of time. We have no such ability, and for those who know a bit about the Heisenberg Uncertainty Principle (HUP), one can already tell that such a statement violates this principle.
     
    Last edited by a moderator: May 4, 2017
  4. Apr 2, 2009 #3
    Google K orbital electron capture.
     
  5. Apr 2, 2009 #4
    The only case when atomic electrons interact with the nucleus is in a type of beta decay called K capture, when a proton in the nucleus does not have enough energy to decay to a neutron and a positron, but does have enough energy to decay to a neutronif it can capture an electron from the K shell. Beryllium-7 is an example.
     
  6. Apr 2, 2009 #5

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    Um...not exactly. An electron interacts electromagnetically with a nucleus, and there is a small correction to the atomic energy levels due to the electron spending a fraction of its time inside the nucleus.

    Not exactly. Na-22, for example can and does emit positrons but also has a 10% branching ratio for electron capture.


    Yes, that is correct.
     
  7. Apr 2, 2009 #6

    alxm

    User Avatar
    Science Advisor

    Do you have a ref. for that? I've never heard of such a correction being done.
    Obviously there's an effect, since the nucleus is not the infinitesimal point charge it's usually modeled as, but it's still dang small. I can't imagine the effect being larger than something on the parts-per-million scale of the electronic energy. (and certainly smaller than the thermal energy at any reasonable temperature, making it physically insignificant)
     
  8. Apr 2, 2009 #7
    Is there another force that counteracts the force of charge trying to pull them together?
    If not, then why the electron won't fall into the proton?
     
  9. Apr 3, 2009 #8
    Gravitating a little closer to the OP question...

    A free neutron decays into a proton, an electron and an anti nuetrino in about 10 minutes. A free neutron is free--it's not inside a nucleus. The resultant particles go buzzing off in all directions, each with some kinetic energy. So the opposite charges of the electron and positron are not enough to keep them bound together. It takes some energy to get them to stick together into one particle.

    (Or maybe the question was 'why don't an electron and proton anihilate each other? But I think Invinoveritas was scared away by the 10 dollar words.)
     
    Last edited: Apr 3, 2009
  10. Apr 3, 2009 #9
    Thank you for all your answers.

    What if there was a way to increase gravity between the Proton and the Electron to the point it overcame the forces counteracting the forces keeping them apart.

    Ideas on what would happen?
    What would happen to the energy that was previously keeping them apart?

    I apologize for the simple questions.
     
  11. Apr 3, 2009 #10

    alxm

    User Avatar
    Science Advisor

    Except for the occurrence of electron capture, nothing. And depending on the nucleus, electron capture ranges from 'rare' to 'not even once in the lifetime of the universe'.

    For an s-orbital electron, the nucleus (r=0) is in fact the most likely point in space to find the electron. (but not the most likely radius)

    There's no energy keeping them apart. It's just that an electron that's close to the nucleus, like an object that's fallen towards the ground, has a high kinetic energy. But unlike an object falling to the ground, an electron can't 'discard' that energy. So if it's there, it's not going to stay there for long.

    The 'problem' of electrons 'falling into the nucleus' predates quantum physics. Classically, an electron can emit its kinetic energy and 'should' fall into the nucleus and just sit there.
     
    Last edited: Apr 3, 2009
  12. Apr 3, 2009 #11

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    This is what lead one to consider quantum mechanics: "why does not the electron fall into the proton?"

    The easiest answer is that the form of the solutions to the Schrödinger Equation prevents this, only in the ground state, there is a non zero probability for the electron to be located at the origin (where the nucleus resigns) - we have to forget about that particles are tiny balls with classical forces acting between them.

    Second is that from QM, we get something called the Heisenberg uncertainty relation, the electron can not be located at a specific position with 100% certainty, only with less. Thus one can only talk about a probability per unit time that an electron undergoes inverse beta decay with a proton in the nucleus.

    So there is no additional force, we just have to forget about our classical, intuitive picture of particles as being tiny balls with classical forces acting on them.
     
  13. Apr 3, 2009 #12

    Thank you.
    My entire understanding of an atom was very far off.



    Please correct me if you have time.

    Bohr's atom says that electrons must be in orbit around the nucleus but that this could not alone stabalize and atom.

    "An accelerated electric charge radiates energy and a circular motion constitutes acceleration"

    Classical physics (Maxwell's equation) says that the electron would radiate energy away and spiral into the nucleus.

    I understood that the there were three basic forces involved in this "balance"

    1. The gravity attracting the Proton and the election
    2. The unlike charge attraction
    3. The large atomic force counteracting the first two.

    very wrong?
     
  14. Apr 3, 2009 #13

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    well yes, since I just said that there is no additional 'force',

    there are two forces involved, whereas gravity is 10^-19 times weaker than EM-force. The reason for the electron not spiralling down to the nucleus due to attractive EM-force is just the imposing of certain physical boundary conditions to the Schrödinger equation, which isthe "equation of motion" at quantum level.
     
  15. Apr 3, 2009 #14
    What would you call copper-64? The only thing it doesn't do is capture positrons.
     
  16. Apr 3, 2009 #15

    DrChinese

    User Avatar
    Science Advisor
    Gold Member

    To the OP: Not taking away from malawi_glenn's explanation, which is correct...

    It may help you to replace your current picture of an electron and a proton being magnetically attracted with a more descriptive and accurate one: The attraction is for the electron to be pulled into an inner orbital of the proton (nucleus). I.e. the attraction is to pull the electron into a position which is a solution to the Schrödinger equation. The concept of the magnets makes you think that the attraction is absolute at any distance, and it is not.

    In fact: if you could place an election inside the first orbital (which is conceivable), then the electron would tend to move AWAY from the proton (rather than towards it as you might otherwise expect). This makes sense in terms of the equations which *correctly* describe the electron and proton, but makes NO sense if you picture a couple of magnets. Orbitals are not orbits, and charged particles are not magnets. So ultimately, you must replace one model with another if you want to understand what is really going on at a deeper level.

    By the way, the same analogy applies with Newtonian Gravity vs. Einsteinian Gravity. You replace one model (which is simple and easy to understand) with a better one (which is far more accurate when accuracy matters).
     
  17. Apr 3, 2009 #16

    Thank you.

    I was just thinking about how great it would be if you could force an atom to collapse itself and release energy in that process.
     
  18. Apr 3, 2009 #17
    It's the energy inside an eletron that makes it get farther from the nucleos, right? Such can be proved because energized eletrons skip distances.
    So, follow my though: if an eletron emit a foton with a energy difference equivalent it's orbit and de nucleos, it skips to the nucleos and thus collide with a proton.
    There's only one way to evade that, that is considering that the nucleos canNOT be considered an eletrosphere, and if you prove that you solve the puzzle right?
    Sorry if there any errors on my logic, I'm new to this area and would appreciate corrections.
    Gedatsu.
     
  19. Apr 3, 2009 #18

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    I'm away from my textbooks, but I'm pretty sure it's a problem in Liboff and/or Schiff.

    It is a small effect, but it's important in that it breaks the n-L degeneracy. Also, for muonic atoms, it's a larger effect.
     
  20. Apr 3, 2009 #19
    Your estimation is in the right ballpark, but you are wrong that it can not be measured.
    Proton Structure Corrections to Hydrogen Hyperfine Splitting
    Proton structure corrections to electronic and muonic hydrogen hyperfine splitting
     
    Last edited: Apr 3, 2009
  21. Apr 4, 2009 #20

    malawi_glenn

    User Avatar
    Science Advisor
    Homework Helper

    You would then need energy to do that, and since atoms are weakly bound, you would not gain that much. The energies in atoms are of the order 10eV, whereas in nuclei the energies are of the order 1MeV, i.e 100 000 times bigger.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook