Question

Neon has three naturally occuring isotopes. The abundance of 20Ne is 90.48% and 22Ne is 9.25%. What is the percent abundance of 21Ne?

Answer 1

Answer: The percent abundance of Ne-21 isotope is 0.27 %

Explanation:

Average atomic mass of an element is defined as the sum of masses of each isotope each multiplied by their natural fractional abundance.

Formula used to calculate average atomic mass follows:

$\text{Average atomic mass }=\sum_{i=1}^n\text{(Atomic mass of an isotopes)}_i\times \text{(Fractional abundance})_i$   .....(1)

Let the fractional abundance of Ne-21 isotope be x

• For isotope 1 (Ne-20) :

Mass of isotope 1 = 20 amu

Percentage abundance of isotope 1 = 90.48 %

Fractional abundance of isotope 1 = 0.9048

• For isotope 2 (Ne-21) :

Mass of isotope 2 = 21 amu

Fractional abundance of isotope 2 = x

• For isotope 3 (Ne-22) :

Mass of isotope 3 = 22 amu

Percentage abundance of isotope 3 = 9.25 %

Fractional abundance of isotope 3 = 0.0925

Average atomic mass of neon = 20.18 amu

Putting values in equation 1, we get:

$20.18=[(20\times 0.9048)+(21\times x)+(22\times 0.0925)]$

x = 0.0027

Percentage abundance of Ne-21 isotope = $(0.0027\times 100)=0.27\%$

Hence, the percent abundance of Ne-21 isotope is 0.27 %