Question

The three stable isotopes of neon: $\begin{array}{c}20\\ 10\end{array}Ne,\begin{array}{c}21\\ 10\end{array}Ne$ and $\begin{array}{c}22\\ 10\end{array}Ne$ have respective abundances of $90.51\%,0.27\%$ and $9.22\%$. The atomic masses of the three isotopes are $19.99u,20.99u$ and $21.99u$, respectively. Obtain the average atomic mass of neon?

Answer 1

Given, Atomic mass of $\begin{array}{c}20\\ 10\end{array}Ne,m_1=19.99u$
Abundance of $\begin{array}{c}20\\ 10\end{array}Ne,n_1=90.51\%$
Atomic mass of $\begin{array}{c}21\\ 10\end{array}Ne,m_2=20.99u$
Abundance of $\begin{array}{c}21\\ 10\end{array}Ne,n_2=0.27\%$
Atomic mass of $\begin{array}{c}22\\ 10\end{array}Ne,m_3=21.99u$
Abundance of $\begin{array}{c}22\\ 10\end{array}Ne,n_3=9.22\%$
The atomic mass of Neon atom is:
$m=\frac{m_1{n}_1+m_2{n}_2+m_3{n}_3}{n_1+n_2+n_3}$
$=\frac{19.99\times 90.51+20.99\times 0.27+21.99\times 9.22}{90.51+0.27+9.22}$
$=20.1771u$
Final Answer: 20.18