The three stable isotopes of neon: 20 21 2210 10 Ne, Ne and Ne 10 haverespective abundances of 90.51%, 0.27% and 9.22%. The atomicmasses of the three isotopes are 19.99 u, 20.99 u and 21.99 u,respectively. Obtain the average atomic mass of neon.

Given: The atomic masses of neon isotopes 10 20 Ne, 10 21 Ne and 10 22 Ne are 19.9 u, 20.99 u and 21.99 u respectively and the abundances of neon isotopes 10 20 Ne, 10 21 Ne and 10 22 Ne are 90.51%, 0.27% and 9.22% respectively.

The average atomic mass of neon is given as,

m= m 1 η 1 + m 2 η 2 + m 3 η 3 η 1 + η 2 + η 3

Where, the atomic masses of neon isotopes 10 20 Ne, 10 21 Ne and 10 22 Ne are m 1 , m 2 and m 3 respectively and the abundances of neon isotopes 10 20 Ne, 10 21 Ne and 10 22 Ne are η 1 , η 2 and η 3 respectively.

By substituting the given values in the above formula, we get

m= 19.99×90.51+20.99×0.27+21.99×9.22 90.51+0.27+9.22 = 1809.2949+5.6673+202.7478 100 = 2017.71 100 =20.1771 u

Thus, the average atomic mass of the neon is 20.1771 u.