Relative Formula Mass

• The relative atomic mass (symbol = Ar) of an element is the weighted average mass of its naturally occurring isotopes
• You calculate the relative formula mass (symbol = Mr) of a compound by adding up all the relative atomic masses of all the atoms present in the formula of the compound
• The elements hydrogen, oxygen, nitrogen, chlorine, bromine, iodine and fluorine exist as diamotic molecules. This means that in equations their relative formula masses are twice their relative atomic mass
• All other elements are represented by just their symbols in an equation. So their relative formula mass is equal to their relative atomic mass