Naturally occurring bromine is composed of 50.7% of 79Br and 49.3% of 81Br. Atoms of 79Br have a mass of 78.9183 u and those of 81Br have a mass of 80.9163 u. Calculate the average atomic mass of bromine. Enter your answer with 3 significant digits.

79.9 u

Explanation:

Given data

Isotope Mass Abundance

⁷⁹Br 78.9183 u 50.7% (0.507)

⁸¹Br 80.9163 u 49.3% (0.493)

We can calculate the average atomic mass (am) of bromine using the following expression.

am = ∑mi * abi

where,

mi: mass of the isotope

abi: abundance of the isotope

am = 78.9183 u * 0.507 + 80.9163 u * 0.493

am = 79.9 u

The atomic mass of bromine is 79.9 u

Explanation:

Step 1: Data given

Isotopes of Bromine:

79Br = 50.7 % with a mass of 78.9183 u

81Br = 49.3 % with a mass of 80.9163 u

Step 2: Calculate the average atomic mass of bromine

Atomic mass of bromine = 0.507*78.9183 + 0.493*80.9163

Atomic mass of bromine = 79.9 u

The atomic mass of bromine is 79.9 u