Chemical Forums
Chemistry Forums for Students => High School Chemistry Forum => Topic started by: gracie7 on December 18, 2009, 11:33:26 AM
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I cannot figure out why the atomic wt. for oxygen is less than 16 (i.e., 15.999), when its three main, stable isotopes have weights of 16, 17, and 18. Can anyone please explain this to me?
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Naturally occurring oxygen is composed of three stable isotopes, 16O, 17O, and 18O, with 16O being the most abundant (99.762% natural abundance).
I would say it's due to rounding up of the actual weights rather than reporting to a load of decimal places for each isotope.
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What is EXACT mass of 16O?
Hint: it is not 16.
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http://en.wikipedia.org/wiki/Isotopes_of_oxygen