Question

Lithium has two known stable isotopes- lithium-6 and lithium-7. Lithium-6 has an isotopic mass of 6.015 amu and percent abundance of 7.59%; lithium-7 has a mass of 7.016 amu at 92.41 % abundance. Calculate the average atomic mass of lithium.

Answer 1

For isotope 1 (lithium-6), atomic mass = $6.015\times 7.59/100=0.4565385$

For lithium-7, atomic mass$=7.016\times 92.41/100=6.4834856$

Average atomic mass of lithium$=0.4565385+6.4834856=6.9400241 amu$