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Why is C not 12g/mole?

  1. May 14, 2006 #1
    In my table of elements, C is listed as having a weight of 12.0107. I presume it means 12.0107g/mole of carbon. I thought Carbon was defined to be 12g per mole?
  2. jcsd
  3. May 14, 2006 #2
    No, the mole was defined to be 12g of the Carbon-12 isotope, not of the naturally occuring isotope mix.
  4. May 14, 2006 #3
    So that weight of C was taken as all types of carbon in nature, not just the 12 isotope. It would also suggest there are more heavier isotopes of carbon than lighter ones in nature.
  5. May 14, 2006 #4
  6. May 16, 2006 #5
    the amu of an atom is an average of the most common occuring isotopes
  7. May 16, 2006 #6
    Huh? A.m.u. is a unit of mass.
  8. May 16, 2006 #7
    umm...ya, thus, atomic mass unit :smile:
  9. May 19, 2006 #8
    Yes, but the a.m.u. is the mass of a nucleon. You're confusing it with r.a.m., or relative atomic mass - which is related to the proportion of isotopes, as Rach3 said.
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