Question

Lithium has TWO common isotopes: `""^6Li` has `7.42%` abundance; and the other isotope is `""^7Li`. What is the average atomic mass of lithium?

Answer 1

The atomic mass quoted on the Periodic Table is the WEIGHTED average of the individual isotopic masses....

Explanation:

We got `""^6Li` with `7.42%` abundance, and `""^7Li` with (necessarily!) `(100-7.42)%` abundance....

And thus, `Li_"average mass"={6xx7.42%+7xx92.58%}*"amu"`

`=6.93*"amu"`