Question

What is the average atomic mass of bromine? One isotope of bromine has an atomic mass of $78.92\text{amu}$ and a relative abundance of $50.69\%$. The other major isotope of bromine has an atomic mass of $80.92\text{amu}$ and a relative abundance of $49.31\%$?

Answer 1

Step 1. Average atomic mass

• There are many isotopes for many naturally occurring elements.
• The average atomic mass of that element can be calculated by taking into consideration the existence of various isotopes and their relative abundance (percent occurrence).

$\text{Average atomic mass}={\mathit{\text{f}}}_{\mathit{1}}{M}_1+f_2{M}_2+\dots +f_n{M}_n$

Here, $f_1,f_2,f_n$ represents the relative abundance of the isotope and $M_1,M_2,M_n$ is the atomic mass of the isotope.

Step 2. Calculation of average atomic mass of bromine

From the given data average atomic mass of bromine can be calculated as:$0.5069\times \left(78.92\text{u}\right)+0.4931\times \left(80.92\text{u}\right)$

=$40.00\text{u}+39.90\text{u}$

=$79.90\text{u}$

Hence, the average atomic mass of Bromine is $79.90\text{u}$.