An imaginary element Y occurs 30% of the time with a mass of 57.9 a.m.u. The remaining sample of Y has a mass of 60.9 a.m.u. What is the average atomic mass of Y?
In essence, this means that each stable isotope will contribute to the average atomic mass of the element In proportion to its abundance.
#color(blue)(|bar(ul(color(white)(a/a)"avg. atomic mass" = sum_i "isotope"_i xx "abundance"_icolor(white)(a/a)|)))#
This equation uses decimal abundance, which is simply percent abundance divided by
So, you know that your imaginary element
How do you know that this second isotope has a
That is the case because the percent abundances of the stable isotopes must add up to give
The average atomic mass of
#"avg. atomic mass" = "57.9 u" xx 30/100 + "60.9 u" xx 70/100#
#"avg. atomic mass " = color(green)(|bar(ul(color(white)(a/a)" 60.0 u"color(white)(a/a)|)))#