Question

calculate the average atomic mass of lithium to the nearest thousandth, which occurs as two isotopes that have the following atomic masses and abundances in nature: 7.30% at 6.017 amu, and 92.70% at 7.018 amu

Explanation:

Step1: Convert percentages to decimals

For the first isotope, \(7.30\% = \frac{7.30}{100}=0.073\)
For the second isotope, \(92.70\%=\frac{92.70}{100} = 0.927\)

Step2: Calculate the contribution of each isotope

Contribution of first isotope: \(0.073\times6.017\)
\(0.073\times6.017 = 0.439241\)
Contribution of second isotope: \(0.927\times7.018\)
\(0.927\times7.018=0.927\times(7 + 0.018)=0.927\times7+0.927\times0.018 = 6.489+0.016686 = 6.505686\)

Step3: Sum the contributions

Average atomic mass \(= 0.439241+6.505686\)
\(= 6.944927\approx6.945\) (to the nearest thousandth)

Answer:

\(6.945\) amu