Question

average atomic mass (2.5)
calculate the average atomic mass of each of the following elements.

1. lithium

Explanation:

Step1: Multiply isotope mass and its decimal abundance for Lithium - 6

$6.015\times0.0074$

Step2: Multiply isotope mass and its decimal abundance for Lithium - 7

$7.016\times0.926$

Step3: Sum the two products

$(6.015\times0.0074)+(7.016\times0.926)$

First, calculate $6.015\times0.0074 = 0.044511$.

Second, calculate $7.016\times0.926=7.016\times(1 - 0.074)=7.016-7.016\times0.074=7.016 - 0.519184 = 6.496816$.

Then sum: $0.044511+6.496816 = 6.541327\approx6.54$ (rounded to two decimal places)

Answer:

The average atomic mass of lithium is approximately $6.54$ amu.