The average atomic weight of lithium is 6.941 amu. The two...

The average atomic weight of lithium is 6.941 amu. The two naturally occurring isotopes of lithium have the following masses: $^{6} \mathrm{Li}, 6.01512 \mathrm{amu} ;^{7} \mathrm{Li}, 7.01600$ amu. Calculate the percent abundance of $^{6} \mathrm{Li}$ and $^{7} \mathrm{Li}$ in naturally occurring lithium.

The average atomic weight of lithium is 6.941 amu. The two naturally occurring isotopes of lithium have the following masses: $^{6} \mathrm{Li}, 6.01512 \mathrm{amu} ;^{7} \mathrm{Li}, 7.01600$
amu. Calculate the percent abundance of $^{6} \mathrm{Li}$ and $^{7} \mathrm{Li}$ in naturally occurring lithium.

Key Concepts

Atomic Weight

Atomic weight represents the average mass of the atoms of an element, taking into account the masses of its isotopes and their relative abundances. This value is not the mass of a single atom but rather a weighted average that reflects how much of each isotope is naturally present.

Isotopes

Isotopes are variants of a chemical element that have the same number of protons but different numbers of neutrons, leading to different masses. In many elements, multiple isotopes occur naturally, and their individual masses contribute to the overall atomic weight of the element.

Weighted Average Calculation

The weighted average calculation is a method used to determine the average atomic weight of an element based on the masses of its isotopes and their relative abundances. Each isotope's mass is multiplied by its fractional abundance, and the sum of these products yields the overall atomic weight of the element.

Percent Abundance Determination

Percent abundance determination involves setting up equations that account for both the weighted average atomic weight and the fact that the total abundance of all isotopes must equal 100%. By solving these equations, one can calculate the relative percentage of each isotope present in a naturally occurring sample of the element.

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