For example: "ChemTeam-42 and ChemTeamium-44 exist. You may want to compare them to the more exact abundances which are in the equation set up at the top of the page.Ĭomment Two: only the mass numbers may be given if the element is a made-up one. The consequence of using 14 and 15 rather than the exact values is that we will get slightly approximate answers for the two abundances. Please notice that the mass numbers (14 and 15) are quite close to the exact values. I advise you to ask your instructor what the question wants you to do if only the mass numbers are provided in the problem. However, in this Internet era, it is easy to look up the values on-line.
The two abundances always add up to one (or, if you prefer, 100%)Ĭomment One (see end of problem for another comment): sometimes the exact weights of the isotopes are not provided in the problem. Notice that the abundance of N-14 is assigned 'x' and the N-15 is 'one minus x.' This is the "trick" refered to above. Given nitrogen's atomic weight of 14.007, what is the percent abundance of each isotope? Problem #1: Nitrogen is made up of two isotopes, N-14 and N-15. I'll show how using the above nitrogen example. So, the trick is to express both abundances using only one unknown. That's right, they add up to 100% (or, since we use decimal abundances in the calculation, 1.00). Think about the sum of the percent abundances of the TWO isotopes. You would be right, except that there is a trick. However, you might protest that we have two unknowns, but only one equation. In this tutorial, the unknown values calculated are the TWO percent abundances. In the other tutorial, the average atomic weight is the unknown value calculated. (exact weight of isotope #1) (abundance of isotope #1) + (exact weight of isotope #2) (abundance of isotope #2) = average atomic weight of the element Let's start by repeating the solution for nitrogen from the Average Atomic Weight tutorial:
Calculate the isotopic abundances from the average atomic aeight and isotopic weights Calculate the isotopic abundances when given the average atomic weight and the isotopic weightsĬalculate the average atomic weight when given isotopic weights and abundances
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