Relative formula mass

• The relative atomic mass is the average mass of all the isotopes of that element and is denoted with (Ar)
• The relative formula mass (Mr) is found by adding together the relative atomic masses of all the elements in that compound's molecular formula.
• Calculating percentage mass

  Ar of element x number of element / Mr of the compound
• Average Atomic Mass = Sum of Isotopic Abundances x Isotopic Masses / Total abundance