Strontium consists of four isotopes with masses of 84 (abundance 0.50%), 86 (abundance of 9.9%), 87 (abundance of 7.0%), and 88 (abundance of 82.6%). Calculate the atomic mass of strontium.

87.62 u

Explanation:

The atomic mass of Sr is the weighted average of the atomic masses of its isotopes.

We multiply the atomic mass of each isotope by a number representing its relative importance (i. e., its percent of the total).

Set up a table for easy calculation

0.0050 * 83.91 u = 0.420 u

0.099 * 85.91 u = 8.505 u

0.070 * 86.91 u = 6.084 u

0.826 * 87.91 u = 72.61 u

TOTAL = 87.62 u