Relative Atomic Mass

The element chlorine has two isotopes, Cl³⁵ and Cl³⁷. The relative abundances for Cl³⁵ and Cl³⁷ are 3 and 1 respectively. Using the information given, calculate the relative atomic mass (A_r) of chlorine.

To calculate the A_r when relative abundances are given:

1. multiply the mass of each isotope with its relative abundance
2. add the obtained values together
3. divide the total value by the sum of the relative abundances

Calculation for above question:
(35 x 3) + (37 x 1) = 142142/4 = 35.5
so the answer is 35.5