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Relative atomic mass of an element ?

  1. Sep 12, 2004 #1
    relative atomic mass of an element ????

    A sample of neon was found to cotain 90.9% of 20Ne, 0.26% of 21Ne, & 8.8% of 22Ne, Calculate the relative atomic mass of neon.
    this is what i'v done so far (90.9x 20)+ (0.26x21)+(8.8x22)= 2017/?
    i dont know what to devide it by :confused: ??? I'm not given a mass spectra?
    why r relative atomic masses for some elements not whole numbers, is it because they r isotopes????
  2. jcsd
  3. Sep 12, 2004 #2
    Divide by 100.

    That will get you 20.17

    Yes, they are not whole numbers because of isotopes. That's what you're taking account for by finding the relative atomic mass.
  4. Sep 12, 2004 #3
    Thanx, i did the question again and i got 20.16 this is what i did (90.9/100x20)+(0.26/100x21)+(8.8/100x22)= 20.16
  5. Sep 12, 2004 #4
    Either way works. :)
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