If I know the abundance percent, number of isotopes and mass(amu), how do I identify an element?

Question

anonymous · Answer

I figures out how but the answer I got cannot be possible because the atomic weight does not exist on the periodic table.
To get the atomic weight, I multiplied 6.015(mass a) to 7.5(abundance a) and got 45.1125. Then I multiplied 7.016(mass b) to 92.5(abundance b) and got 648.98. I then added the two products together and got 694.0925 which, according to my source,. is supposed to be my atomic number.
Did I do something wrong?

jfraser · Answer

You have percentages of 7.5% and 92.5%, but you have to convert the percentages into abundances to find the average mass properly. Divide your final answer by 100, and you've got the proper atomic mass, which is lithium

anonymous · Answer

Oh okay, thank you!