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I Force that binds atoms

  1. Jan 2, 2018 #1
    So I now understand the forces within an atom though my question is, what force(s) keeps atoms together? So let's say 2 hydrogen atoms are present. What force(s) keeps them together to make it H2? My thought it would be electromagnetic force. But hydrogen is neutral so they wouldn't attract to eachother would they?
     
  2. jcsd
  3. Jan 2, 2018 #2

    Orodruin

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    You are correct that the interaction is electromagnetic. It is a matter of how the electrons and the nuclei interact and those are charged.

    Very simplified: If you have two hydrogen atoms infinitely far away from each other all energy levels of the electrons will be degenerate. As the protons come closer together, this degeneracy is broken and there will be one symmetric wave function energy level where the electrons on average will be likelier to stay between the protons that has a lower energy than the antisymmetric one. Placing both electrons in this energy level (possible due to spin) is a double covalent bond.

    A similar question would be why negatively charged ions can exist.
     
  4. Jan 3, 2018 #3

    sophiecentaur

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    A more 'noddy' description (a description without QM that would have satisfied a Victorian, perhaps) could be that each atom shares each electron. The attraction between each proton and each electron pulls the two protons together until their mutual repulsion balances out the attraction. This covalent bonding happens in many other molecules and describes how large molecules with chains of Carbon atoms (in particular) can exist. School Chemistry describes the bonding between some atoms of different elements as 'ionic bonding'. In that case the model is that one electron moves from one atom to the other and actually forms two ions. (Google it).
    Also, Metals are held together very strongly because the outer electrons are shared by many adjacent atoms, (a form of covalent bonding, if you like). As the metal is stretched, the electrons keep pulling and they latch onto different atoms. So the metal doesn't break because other bonds are formed.
     
  5. Jan 3, 2018 #4

    mjc123

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    Two electrons in a bonding orbital constitute a single covalent bond. Just one electron (as in H2+) would give a bond of order 1/2.
     
  6. Jan 3, 2018 #5
    So no electromagnetic force but intramoleculair forces?
    Which you can divide into metallic bond, ionic bond, polar covalent bond and non-polar covalent bond?
    Or does intramoleculair force have anything to do with electomagnetic force?
     
  7. Jan 3, 2018 #6
    Can somebody explain this? ^

    And what are symmetric and unsymmetric waves?
    I think I found an answer: but i still don't get what Orodruin was saying
    symmetric waves: particle interchange with bosons
    antisymmetric waves: particle interchange with ferminons
     
    Last edited: Jan 3, 2018
  8. Jan 3, 2018 #7

    Orodruin

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    No. The symmetric/antisymmetric here refers to a parity transformation of the spatial wavefunction. In general, if you have a symmetric potential as in the case of the two protons, the wave function of the energy eigenstates will be either symmetric or anti-symmetric.

    The simplified simplified version is. The lowest energy state is one where the electrons orbit both protons. This is state has lower energy than the hydrogen atoms you would get pulling the protons apart.
     
  9. Jan 3, 2018 #8

    sophiecentaur

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    Where did you get that idea? I was talking about electrons and protons. That's electrostatic (Coulomb) Force.
    I'll leave @Orodruin to answer your question to him.
     
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