Lithium has two naturally occurring isotopes: lithium−6 and lithium−7. Lithium−6 has a mass of 6.01512 relative to carbon−12 and makes up 7.47 percent of all naturally occurring lithium. Lithium−7 has a mass of 7.016 compared to carbon−12 and makes up the remaining 92.53 percent. According to this information, what is the atomic weight of lithium?

6.941

Explanation:

Step 1:

Representation.

Let Lithium−6 be isotope A

Let Lithium−7 be isotope B

Let the abundance of isotope A (Lithium-6) be A%

Let the abundance of isotope B (Lithium-6) be B%

Step 2:

Data obtained from the question. This includes:

Mass of isotope A (Lithium−6) =

6.01512

Abundance of isotope A (Lithium−6) = A% = 7.47%

Mass of isotope B (Lithium−7) = 7.016

Abundance of isotope B (Lithium−7) = B% = 92.53%

Atomic weight of lithium =?

Step 3:

Determination of the atomic weight of lithium. This is illustrated below:

Atomic weight = [(Mass of AxA%)/100] + [(Mass of BxB%)/100]

Atomic weight = [(6.01512x7.47)/100] + [(7.016x92.53)/100]

Atomic weight = 0.449 + 6.492

Atomic weight of lithium is 6.941

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