Bromine has two naturally occurring isotopes (Br-79 and Br-81) and has an atomic mass of 79.904 amu. The mass of Br-81 is 80.9163 amu, and its natural abundance is 49.31%. Calculate the mass and natural abundance of Br-79.

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Identify the given information: the atomic mass of bromine is 79.904 amu, the mass of Br-81 is 80.9163 amu, and its natural abundance is 49.31%.

Let the mass of Br-79 be denoted as M_{79} and its natural abundance as A_{79}. Since the total natural abundance must be 100%, A_{79} = 100% - 49.31%.

Set up the equation for the average atomic mass of bromine: 79.904 = (M_{79} * A_{79} + 80.9163 * 49.31%) / 100.

Substitute A_{79} = 100% - 49.31% into the equation: 79.904 = (M_{79} * (100% - 49.31%) + 80.9163 * 49.31%) / 100.

Solve the equation for M_{79} to find the mass of Br-79.

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Isotopes

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses. For example, bromine has two isotopes, Br-79 and Br-81, which differ in their neutron count. Understanding isotopes is crucial for calculations involving atomic mass and natural abundance.

Atomic Mass and Weighted Average

The atomic mass of an element is a weighted average of the masses of its isotopes, taking into account their natural abundances. This means that the atomic mass reflects the contribution of each isotope based on how common it is in nature. In the case of bromine, the atomic mass of 79.904 amu is derived from the contributions of both Br-79 and Br-81.

Natural Abundance

Natural abundance refers to the relative proportion of each isotope of an element found in nature, usually expressed as a percentage. For bromine, the natural abundance of Br-81 is given as 49.31%, which allows us to calculate the abundance of Br-79 by subtracting this value from 100%. This concept is essential for determining the isotopic composition of an element.