Question

How does abundance contribute to the average atomic mass of an element?

Answer 1

Percentage abundance of isotopes determines relative atomic mass.

Explanation:

Chlorine has `A_r` value of 35.5 as there are two isotopes, Cl-35 and Cl-37. These do not occur in equal proportions. In every 100 atoms, there are 75 of Cl-35 and 25 of Cl-37. Therefore, the `A_r` value is calculated as

`((35 xx 75) + (37 xx 25))/100 = 35.5`