Question

What is the average atomic mass of the element?

An element, X, has two isotopes, X-14 and X-15. Use the data in the table to find the average atomic mass of element X. Isotope Atomic Mass Abundance (%) X-14 14.003 99.636 X-15 15.000 0.364

The average atomic mass of element X is blank amu.

Answer 1

The average atomic mass of element X is 14.007 u.

The average atomic mass of X 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 % abundance).

Thus,

0.996 36 × 14.003 u =13.952 03 u

0.003 64 × 15.000 u = 0.054 60 u

__________TOTAL = 14.007 u