... Most elements can be found on earth (with the exception of those elements that too unstable and thus must be synthesized in the laboratory). Since all elements have isotopes then we must consider how much of one isotope of an element exists versus another isotope of the same element. These are called the "natural" abundances on earth. Natural Abundances: Suppose we go to a cave and mine element "X". After careful analysis we find that in our sample of element X there exists three isotopes: Xa, Xb and Xc. Moreover, we find that out of every 100 atoms the various isotopes are distributed as follows: For Every 100 atoms of X Isotope No. of atoms Xa 30 Xb 60 Xc 10 Then we say that the natural percent abundance of Xa is 30 %, of Xb is 60 % and of Xc is 10 %. Next, we can inquire what the mass of element ...

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