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Atomic radii

  1. Jun 13, 2003 #1
    Apologies for raising this question again, but it has finally dawned on me that as the Tables of Elements give an average mass (i.e. for all isotopes of each element) as the Relative Atomic Mass for that element; then my question is -
    Is the figure quoted for Atomic Radii also an average figure?

    Note that none of the tables actually say that the radius is an average, I just wonder if I am suppose to make that connection myself. Given that the two measurements are always in different sections of the tables it seems to show a lack of clarity on the part of the authors.
  2. jcsd
  3. Jun 13, 2003 #2


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    Educated guess: Atomic radii are essentially defined by the electronic structure of the atom. Different isotopes of the same element have the same number of electrons, so I strongly suspect that they have the same radius. The radius of the nucleus is very small compared to that of the atom, so the difference in the number of neutrons shouldn't have any effect.
  4. Jun 14, 2003 #3
    This was the reply to an earlier question but Mcgraw-Hills Encyclopedia of Science and several lesser encyclopedias dissagree; they say there is a difference but do not quote any figures.
    There seems to be a lack of clarity on this data.
  5. Jun 14, 2003 #4
    The only book that might contain the atomic radii of isotopes is "Table of Isotopes" by Rb Firestone published by John Wiley and Sons Inc.
    The only copy I have traced is in the British Library-reference section. To far to travel and too expensive to buy. If anyone has access to a copy please let me know what it contains appertaining to isotope radii.
  6. Jun 14, 2003 #5
    May I suggest research in Rydberg atoms. That is atoms in their almost largest excited state with the outermost electron in a high energy level. Note that they can be a much as 100,000 times larger than normal atoms. Case in point: Rydberg atoms acting like hydrogen with n=400 would have a diameter of 10um where as a normal hydrogen diameter is only 1.1*10^-4um.
  7. Jun 15, 2003 #6


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    Using the google search engine for "atomic radius", I found may references with data and descriptions. In all cases, there was no indication of dependency on isotope. Moreover, in describing what the radius means (there were several different definitions, with different numbers), it was always a result of Coloumb forces, where neutrons have no role.
  8. Jun 15, 2003 #7
    That's true and I think he is missing the point that the nucleus doesn't really have anything to do with the radius of an atom because of how electrons act in the cloud.
  9. Jun 15, 2003 #8
    You are correct in respect of the imformation available on the net but wrong in your comment on atoms.
    I have checked three scientific enclopedias on sale at present (i.e. latest editions) and the one in the reference section of the local library. They all state that isotopes of a given element have different radii (two comment on the smallness of the difference) but none gives a table or example.
    As mention previously, the only solution as to whether or not the measurements are known is probably in Firestones 'Table of Elements'. Earlier editions were written by E Browne.
    One encyclopedia does explain why electrons are not wholly responsible for atomic radii, but I could not memorise the details.
    The lack of a definite or authoritive reference on this point leads me to conclude that there is no known answer at present.
  10. Jul 25, 2003 #9
    Please go to Vacuum force model in "theory Developement"
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