Isotopes

Isotopes are atoms of the same element that have different numbers of neutrons in their nucleus. This means they also have different masses. The number of protons in the nucleus is what determines which element an atom is, so isotopes of the same element have the same chemical properties.

To find the ar (relative atomic mass) of an element with isotopes you do the following calculation:

((Ar × Abundance of Isotope 1)+(Ar × Abundance of Isotope 2))/100