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Could another atom be used as the standard for amu?

  1. Jul 4, 2015 #1
    The atom that is used as the standard for the atomic mass scale is the Carbon atom with an atomic number of 6 and a mass number of 12 and this carbon atom is equal to 12 unified atomic mass units. Could another atom be used as the standard, and if so, how would this be accomplished??
  2. jcsd
  3. Jul 4, 2015 #2


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    This sounds like homework. What is your opinion on the question?
  4. Jul 4, 2015 #3
    Sure, any atom could be used. Suppose you wanted to use Lithium 7. Define the mass as exactly 7.0000 amu and then all the other atomic masses get adjusted accordingly.
  5. Jul 4, 2015 #4
    Is there a reason you used four zeros?
  6. Jul 4, 2015 #5
    Because I was too lazy to type 1000 zeros. Exactly 7.00000000000000000000000000 by definition is exact to whatever precision you like.
  7. Jul 4, 2015 #6


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    Another atom has been used, before the standard was changed to carbon-12. This atom was oxygen, or more specifically, oxygen-16.

    The atomic mass unit concept was developed before it was discovered that the chemical elements have various isotopes. Prior to 1929, it was though that oxygen had only one isotope, oxygen-16, which comprises more than 99% of the oxygen found on earth. In 1961, the standard mass unit was changed to carbon-12, which was selected because it would cause the least disruption in measurements already made based on the atomic weight of oxygen-16.

  8. Jul 6, 2015 #7
    You would want the other atom to be readily available, safe to handle, inexpensive, relatively easy to purify, and other convenient qualities. Gee, C-12 meets the criteria! Are you just curious, or do you think there is a problem needing fixing?
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