Question

Neon lamps, is composed of 90.483% of 20ne, 0.271% of 21ne, and 9.253% of 22ne. the 20ne atoms have a mass of 19.992 u, 21ne atoms have a mass of 20.994 u, and those of 22ne have a mass of 21.991 u. calculate the average atomic mass of neon.

Answer 1

20.181 u

The average atomic mass of Ne 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,  

Avg. at. mass

= (0.904 83× 19.992 u) + (0.002 71 × 20.994) + (0.092 53× 21.991 u)

= 18.0894 u + 0.0569 u  + 2.0348 u = 20.181 u