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?
A)10.00 amu
B)20.18 amu
C)20.99 amu
D)62.97 amu

Question

Quizplus · Accepted Answer

To find the atomic mass of neon, we need to take a weighted average of the masses of its isotopes. We can use the percent abundances as weights. 
Atomic mass of neon = (0.9051 x 19.99 amu) + (0.0027 x 20.99 amu) + (0.0092 x 21.99 amu) 
= 18.08849 + 0.056673 + 0.202708 
= 18.34787 amu ≈ 20.18 amu (rounded to two decimal places) 
Therefore, the correct option is B.

Naturally Occurring Neon Exists as Three Isotopes