Bromine has two naturally occurring isotopes (Br-79 and Br-...

Bromine has two naturally occurring isotopes (Br-79 and Br- 81 ) and an atomic mass of 79.904 amu. (a) If the natural abundance of $\mathrm{Br}-79$ is $50.69 \%,$ what is the natural abundance of Br- $81 ?$ (b) If the mass of $\mathrm{Br}-81$ is 80.9163 amu, what is the mass of Br-79?

Bromine has two naturally occurring isotopes (Br-79 and Br- 81 ) and an atomic mass of 79.904 amu.
(a) If the natural abundance of $\mathrm{Br}-79$ is $50.69 \%,$ what is the natural abundance of Br- $81 ?$
(b) If the mass of $\mathrm{Br}-81$ is 80.9163 amu, what is the mass of Br-79?

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Key Concepts

Isotopic Abundance

Isotopic abundance refers to the percent composition of an element's naturally occurring isotopes. When calculating properties such as average atomic mass, the sum of the abundances must equal 100%, and each isotope’s contribution is proportional to its abundance.

Average Atomic Mass Calculation

The average atomic mass of an element is determined by multiplying the mass of each isotope by its fractional abundance and then summing these products. This weighted average approach accommodates the different contributions from each isotope in a natural sample.

Weighted Mean

A weighted mean is used when different data points contribute unequally to the final average. In the context of isotopic masses, each isotope is weighted by its natural abundance, making this method crucial for computing the overall atomic mass of an element.

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