1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Space in an atom

  1. Nov 23, 2009 #1
    What happens to the space in two atoms that fuse together?
    Fusion takes place inside the sun’s core from the protons of two atoms fusing together.
    Is the new atom bigger or has the space between the nucleuses and the electrons remained the same and some space disappears?
  2. jcsd
  3. Nov 23, 2009 #2
    I would think you would basically lose one atom of volume so the sun would physically be denser by volume overall.

    However you have to remember that at the core of the sun the reason they are fusing is because the densities are so extreme as well as their kinetic energy from being so hot, but there should still be space being lost.
  4. Nov 24, 2009 #3
    So to begin no its not the protons that are fusing, its two atoms that are fusing, just thought i should clarify.... Second, I think that If the outer layer of an atom could be though of as a ball if you put two balls together you will see that you cant just lose space, they will become a ball with twice the volume. I dont know If you have ever seen an H2O molecule in a science book or something but if you notice the Hydrogen atoms are very small compared to Oxygen atoms. If in fact space was lost inside of an atom when it was fused together then you will see that the Hydrogen and Oxygen atoms should be the same size..... Note that Oxygen was made by fusion, just like all other elements other than Hydrogen.
  5. Nov 24, 2009 #4
    Oxygen is larger because ithas more electrons in higher orbitals so you are going to lose thenet difference between the 2 fused atoms. I was picturing 2 hydrogen atoms combining to form helium which still uses the first orbital but any element below iron can fuse
  6. Nov 24, 2009 #5


    User Avatar
    Gold Member

    The radius of an atom is largely dependent on its electron shells and how full they are in addition to the obvious one of atomic number.

    Here are a couple of diagrams showing various radii of atoms as a function of their atomic number.
    Note that in most definitely not a smooth curve from small to large. (The top chart reads from left to right then top to bottom, just like a book.) The sawtooth diagram at the bottom shows this very well.

    http://www.avon-chemistry.com/p_table_atomic_rad.jpg [Broken]

    Google or Wiki "atomic radii" for a more in-depth explanation as to how the radius changes with the element.
    Last edited by a moderator: May 4, 2017
  7. Nov 24, 2009 #6
    Never mind i was wrong about that, But to correct you in one fact, Iron can fuse but the only problem is that anything higher and including iron, when fused actually takes energy instead of giving off energy. It wouldnt make sense why we have elements bigger than Iron if anything higher than Iron could not be fused together
  8. Nov 25, 2009 #7
    Well we were talking about fusion at the center of a star during normal behavior so Iron does not fuse specifically due to the reason you stated, all elements above that are created during more energetic events such as supernova. I wasn't saying it was impossible
  9. Nov 25, 2009 #8
    We are talking about the sun with a core temperature of 10^6 K; photons of temperature any higher than about 3000 K are energetic enough to cause dissociation of electrons in hydrogen, so we aren't working with atoms but with a plasma of subatomic particles and highly energetic photons.

    I think that sort of renders the question of "space" irrelevant since all the space in atom comes from the relatively large separation between electrons and nuclei.
  10. Nov 25, 2009 #9
    I agree with Mikey on this. The term "space" needs to be clarified as space between the electrons and nuclei, or space taken up by the actual guts of the atom (particle, whatever).
  11. Nov 25, 2009 #10
    yeah I didnt think about that, the sun is a plasma so its simply free floating nuclei coalescing.
  12. Nov 25, 2009 #11
    Post #8 has the right idea...the original question of "atoms" in fusion is incorrect since it is nucleii that fuse, not atoms.

    The fusion of lighter nuclei, which creates heavier nucleii and free neutrons also complicates comparisons. The strong force, electromagnetic force, binding energy and energy levels operate in complex ways. In addition, some mass is actually converted to energy (is it maybe a few percent?) so I don't know how all those things net out. I am unsure if quark spacing within neutrons and protons always remains fixed; I suspect so.
  13. Nov 25, 2009 #12
    I don't know exactly if heavier nuclei are more dense than lighter ones.. you have some conflicting terms due to electrostatic repulsion, strong quark confinement, etc., seems way beyond what I have learnt. In any case I think the size of any change in radius of the nuclei is totally and utterly negligable compared to their mean free path, of even perhaps their de Broglie wavelength!?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook