The weighted average of the masses of the isotopes of an element

Atomic mass

Explanation:

The weighted average of the masses of the various isotopes of an element makes the atomic mass. This is why most atomic mass values usually have decimals.

In order to calculate the atomic mass of an element using the weighted average masses, we use the expression below:

                    Atomic mass = ∑

Where is the mass of isotope i

            is the abundance of isotope i

The abundance or geonormal abundance is the proportion by which each of the isotope occurs in nature.