Question

If a bromine atom is available in the form of say two isotopes ${}_{35}^{79}Br$(49.7%) and ${}_{35}^{81}Br$ (50.3%), calculate the average atomic mass of the bromine atom.

Answer 1

The average atomic mass can be calculated using the formula,
$\text{Average atomic mass}=A_1\times \frac{X}{100}+A_2\times \frac{Y}{100}$
where,
$A_1,A_2\Rightarrow \text{Atomic masses}$
$X,Y\Rightarrow \text{Respective percentages}$
$A_1=79,A_2=81$
$X=49.7\text{\%},Y=50.3$
$\therefore \text{Average atomic mass}=79\times \frac{49.7}{100}+81\times \frac{50.3}{100}$
$=39.263+40.743$
$=80.006u$