Question

On most periodic tables a single atomic mass is listed instead of the mass numbers for all the stable isotopes. How is this mass related to the different isotopes?

Answer 1

Answer: The mass of the atom is basically the average atomic mass of all the stable isotopes.

Step-by-step explanation:

Average atomic mass 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* \text{(Fractional abundance})_i`

For Example: Taking the element silicon

Three isotopes of Silicon, which are Si-28, Si-29 and Si-30.

Average atomic mass of silicon = 28.086 amu

As, the average atomic mass of silicon is closer to the mass of Si-28 isotope. This means that the relative abundance of this isotope is the highest as compared to the other two isotopes.

Percentage abundance of Si-28 isotope = 92.2%

Percentage abundance of Si-29 isotope = 4.7 %

Percentage abundance of Si-30 isotope = 3.1%

Hence, the mass of the atom is basically the average atomic mass of all the stable isotopes.