Question

Can you determine the average atomic mass for an element if you know only the atomic number and mass number of an atom? If not, what other information would you need?

Answer 1

Answer: To determine the average atomic mass, we require abundance of every isotope in the nature.

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:

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

For Example: There are 3 isotopes of silicon, Si-28, Si-29 and Si-30.

We know that:

Average atomic mass of silicon = 28.086 amu

In order to calculate the average atomic mass of an element, we need the atomic mass of every isotope and also the abundance of every isotope in the nature.

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, to determine the average atomic mass, we require abundance of every isotope in the nature.