Questions: Neon has 2 isotopes, Neon- 20 and Neon-22. Out of every 250 neon atoms, 225 will be Neon-20 (19.992 amu) and 25 will be Neon-22 (21.991 amu). What is the average atomic mass of neon?

Solution Steps

To find the average atomic mass of neon, we need to consider the proportion of each isotope. According to the problem, out of every 250 neon atoms, 225 are Neon-20 and 25 are Neon-22.

The contribution of each isotope to the average atomic mass is calculated by multiplying the mass of the isotope by its relative abundance (proportion).

• For Neon-20: \[ \text{Contribution of Neon-20} = 19.992 \, \text{amu} \times \frac{225}{250} \]

• For Neon-22: \[ \text{Contribution of Neon-22} = 21.991 \, \text{amu} \times \frac{25}{250} \]

Add the contributions of each isotope to find the average atomic mass of neon.

\[ \text{Average Atomic Mass} = \left(19.992 \times \frac{225}{250}\right) + \left(21.991 \times \frac{25}{250}\right) \]

Calculate each term:

• Contribution of Neon-20: \[ 19.992 \times \frac{225}{250} = 17.9928 \]

• Contribution of Neon-22: \[ 21.991 \times \frac{25}{250} = 2.1991 \]

Add these contributions to find the average atomic mass:

\[ \text{Average Atomic Mass} = 17.9928 + 2.1991 = 20.1919 \]

Final Answer