3. Relative Mass

The actual mass of an atom cannot truly be wieghed as it is so small so they compare it to the mass of the carbon-12 isotope, it is a Relative Mass.

Relative Atomic Mass, Ar - this is the average mass of an atom of an element compared to one-twelfth of the mass of the atom carbon-12

Relative Isotopic Mass - this is the mass of an atom of an isotope compared to one-twelfth of the mass of the atom of carbon-12, the relative isotopic mass is the same as the mass number of an…