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Attraction between two Hydrogen Atoms

  1. Dec 12, 2005 #1
    For two hydrogen atoms separated by 3 Angstroms, what is the main force (cause) for the two atoms to move closer toward each other?

    As the atoms get closer, does a different force (cause) dominant the original force that started the attraction?
  2. jcsd
  3. Dec 12, 2005 #2


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    In general, at the atomic or molecular level, the force involved is electromagnetic. The nuclear forces operate only inside the nucleus, while gravity is far too weak to be meaningful for things (atoms and molecules) that are that small.
  4. Dec 12, 2005 #3
    Can you give a reference for the attractive force of two hydrogen atoms at this distance please?
  5. Dec 12, 2005 #4
    Perhaps the van der Waals force ?--which is discussed by Bohm (1951) "Quantum Theory". On pp 477-479 Bohm presents a wave function that "corresponds to a statistical tendency to oscillate in phase, for which both classically and quantum-mechanically the systems are found to attract..." and ..."thus the closer the atoms get the more transfer of energy between the atoms"..."if they oscillate in phase they will attract". The QM equations for this attractive interaction for hydrogen atoms are presented by Pauling & Wilson (1935) "Introduction to Quantum Mechanics..." on page 384 in the section titled " Van der Waals Forces for hydrogen atoms".
  6. Dec 12, 2005 #5
    p 544 of "Fundamentals of Atomic Physics" by A. P. Arya published in 1971 by Allyn and Bacon which references Kolos, W. and C.C.J. Roothons, "Revs. Mod. Phys." Vol 32, p 219 (1960).

    At 3 angstroms the energy value is negative (-) 0.3 eV roughly by the eyeball.

    The cause of the attraction appears to be electrostatic in accordance with the Heitler-London (QM) model of the hydrogen atom. Based on the number of repulsive states (3) vs attractive states (1) the two atoms have roughly a 25% chance of bonding.

    I'm interested to learn about the magnetic factors that must also exist. Thanks.
    Last edited: Dec 12, 2005
  7. Dec 19, 2005 #6
    Can someone else add a bit of enlightment?
  8. Dec 20, 2005 #7

    Meir Achuz

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    Magnetic forces are generally unimportant for the attraction between 2 H atoms. In H energy levels, they lead to fine and hyperfine splitting, which is about 100-10,000 times smaller than the electrostatic effects. At 3 A, the two atoms probably have a dipole-dipole force like van der Waals, or some of the more detailed models mentioned above. When the atoms get within about 1 A of each other, the electron clouds start to overlap and there is then Coulomb attraction of one proton with the other atom's electron, which leads to a molecule. Detailed models for this are very complicated.
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