An element has two naturally-occurring isotopes. The mass numbers of these isotopes are 119 amu and 121 amu, with natural abundances of 5% and 95%, respectively. Calculate its average atomic mass.

Answer 1

Multiply the mass of each isotope by their abundance and add it together to find the average atomic mass:

119(0.05) + 121(0.95) = average atomic mass of the element

*make sure to convert 95% to 0.95 and 5% to 0.05 before you multiply

Hope this helps!