If bromine atom is available in the form of, say, two isotopes

79Br (49.7%) and 81 Br (50.3%). calculate the average atomic

mass of bromine atom.

80 amu

Explanation:

Data Given:

Abundance of Br-79 = 49.7 % = 0.497

mass of Br-79 = 79 amu

Abundance of Br-81 = 50.3% = 0.503

mass of Br-81 = 81 amu

Average atomic mass of bromine atom = ?

Solution:

Formula used to check average atomic mass is as under

Average atomic mass = m₁A₁ + m₂A₂

Where

m₁ and m₂ = mass of isotope 1 and 2 respectively

A₁ and A₂ = abundance or fraction of isotope 1 and 2 respectively

Put values in above formula

Average atomic mass = (79 amu) (0.497) + (81 amu) (0.503)

Average atomic mass = 39.263 + 40.743

Average atomic mass = 80.006 amu

So

Round to four significant figures

Average atomic mass of Br atom = 80 amu