Question

Naturally occurring neon exists as three isotopes. 90.51% is ne-20 with a mass of 19.99 amu, 0.27% is ne-21 with a mass of 20.99 amu, and 9.22% is ne-22 with a mass of 21.99 amu. what is the atomic mass of neon?

Answer 1

The atomic mass of an element is the average relative mass of its atoms as compared with an atom of carbon-12 whose mass is taken as 12. In terms of percentages of different isotopes, the average atomic mass can be determined as follows: $A_{average}$ = ∑($p_{i}$X $A_{i}$)/100. Where, $p_{i}$ is the percentage abundance of isotope with atomic number $A_{i}$.

So, average atomic mass of neon = $\frac{(90.51 X 19.99) + (0.27 X 20.99) + (9.22 X 21.99)}{100}$ = 20.177 amu.