Question

Determine the average atomic mass of helium, which has two isotopes having atomic masses 4.0026 amu and 3.0160 amu. The relative abundance of the two isotopes is 99.9999 percent and 0.0001 percent, respectively.

Answer 1

you just need to multiply each atomic mass by its percent abundance and add the results.

1. 4.0026x (99.9999%)= 4.0026
2. 3.0160z(0.0001%)= 0.000003016

average atomic mass= 4.0026 + 0.000003016= 4.0026