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Inside an atom

  1. Oct 5, 2003 #1
    Newbie here, so go easy. Electrons are negatively charged bodies orbiting around the nucleus, which contains the proton and the neutron. The net charge of the nucleus is positive, so why is there no attracton between the electrons and the nucleus?
     
  2. jcsd
  3. Oct 5, 2003 #2
    Hi Sanjuro,

    I am a newbie too so my explanations wont be as accurate as other members of this board. But I intend to ask a lot of questions myself so I figure I should perticipate in answering some of the questions instead of just asking them :smile:

    There is an attraction between the nucleus and the elections. And this attraction is what holds the atom together. And it is a stable, or balanced, attraction when the electrons equal the number of protons. And when the two parts do not equal each other the attraction is less stable.

    For instance If an atom has 10 electrons, 10 Protons, and 10 Netrons, it is a stable atom and if the atom had feelings it would feel content. But if an atom had 11 electrons, 10 protons, and 10 netrons, it would feel discontent. The orbiting electrons would be pulling on the nucleus more than what the nucleus naturally felt comfortable with, and the atom would want to do something about its unbalanced state.

    It could join up with another atom that was also feeling discontent but instead of the extra electron causeing the second atom to feel discontent lets say the second atom was missing a electron (making it positivly charged) and the two atoms could combine to form a compound.
     
  4. Oct 5, 2003 #3

    chroot

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    Without going into the feelings of the particles involved, one can say simply that, yes, there is electrostatic attraction between nuclei and electrons, which is why atoms form.

    The deeper question, which I assume you are simultaneously asking, is "if there is electrostatic attraction, why do the electrons not fall into the nuclei?"

    The answer to this question is that, in the microscopic world, the fundamental indeterminism of momentum and position prohibits it. In short, when particles like electrons are in potential wells around nuclei, they cannot have any energy -- they can only have specific discrete energies. The lowest of these energies is call the ground state, and there is no way for an electron to get any closer, or have any lower energy, than the ground state. The electrons cannot fall any closer to the nucleus because there are no lower allowed energy states.

    - Warren
     
  5. Oct 5, 2003 #4

    LURCH

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    While we're on the subject, how do the electrons get integrated into the nuclei in a neutron star? The force of gravity appearently overcomes the resistance of the electron to occupy an orbital that is lower than the ground state. But that is counterintuitive, since attempting to force the electron into the nucleus by crushing it should add energy to the system, moving the electrons into a higher orbital. I've never really understood the process behind this.
     
  6. Oct 5, 2003 #5

    Nereid

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    e- + p+ = n + νe
    [edit: inverse neutron decay written correctly (thank you marcus)]
    Bye, bye electron!

    Since the electrons in a white dwarf (say) are already fully degenerate (they occupy all the energy levels allowed), if the (self) gravitational pressure become greater than the degeneracy pressure, where can they go?
    Does anyone know whether, inside a white dwarf, the reaction is exothermic?
     
    Last edited: Oct 6, 2003
  7. Oct 5, 2003 #6

    marcus

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    would you be willing to look at this reaction as well?

    e- + p+ = n + ν

    it seems algebraically hardly any different from what you wrote and I know when a dead star collapses to neutron matter (for instance in supernova) a lot of neutrinos are produced

    I think there may be an elementary argument showing that in a stable white dwarf core the reaction in question is not exothermic
     
  8. Oct 5, 2003 #7

    marcus

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    Somebody might ask Labguy, he knows the nuclear reactions involved in collapse of cores
    Maybe one need not necessarily imagine, as you are doing, the electrons belonging to a certain nucleus being forced down into that individual nucleus

    Perhaps one could imagine iron-sized nuclei being forced to fuse into nuclei of heavier elements and even into larger assemblages that one would not ordinarily call nuclei since they wouldnt have a stable existence normally

    the merger of irons or anything heavier than iron is endothermic
    (iron being the extremum of the curve of binding energy)

    I'm not sure how the electrons get gobbled up or annihilated---Labguy would know at once, and there must be plenty on the web.

    I believe that in the collapse of a dead star the core reactions are endothermic which is a key to the suddenness of the collapse. The fusion of iron to heavier stuff does not produce heat energy to fight the collapse, so once collapse starts nothing resists it

    My hunch is that there are many reactions and some involve gobbling electrons while others involve emitting positrons---as the assemblages of baryons accumulate into pure neutron matter

    either way the electrons get wiped out---either gobbled for breakfast or annihilated at brunchtime by the positrons. A huge storm of neutrinos is produced which is observed with SNe.

    I realize I havent answered your question but may hopefully have provided some grist for the mill, if Im mistaken let me know
     
    Last edited: Oct 5, 2003
  9. Oct 6, 2003 #8

    chroot

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    Neutron stars form from protons and electrons via the inverse beta decay.

    - Warren
     
  10. Oct 6, 2003 #9

    Nereid

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    IIRC, a neutron star forms from the core collapse of a sufficiently massive star, once it runs out of fuel (i.e. when there's only iron etc left in the core). A white dwarf forms when a core ceases to burn, and collapse is halted by (electron) degeneracy pressure. The star's mass is the key factor determining the fate - white dwarf, neutron star, black hole.

    The piece of the puzzle I was missing (I looked it up) is how a core supported by electron degeneracy turns into a neutron core.

    If it's still contracting, electrons are forced into higher and higher levels, until they enter the relativistic realm. Once they are energetic enough (0.8 MeV), the inverse beta reaction can take place. Bye, bye electrons.

    Furthermore, the neutrinos carry away energy, cooling the core further. Highly endothermic. Quite a separate endothermic process from the breakdown of iron.

    Thank you LURCH, a good question.
     
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