Here's why:

* Atomic masses are based on isotopes: Atomic masses are calculated based on the weighted average of the masses of all the naturally occurring isotopes of an element. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.

* Atomic masses are typically whole numbers: While there are decimals in atomic masses due to the weighted average of isotopes, these decimals are usually very small and don't result in numbers like 83.3.

The closest element to an atomic mass of 83.3 is Krypton (Kr), which has an atomic mass of 83.798.