Relative atomic mass
- The symbol for the relative atomic mass is Ar
- This is calculated from the mass number and relative abundances of all the isotopes of a particular element
The top line of the equation can be extended to include the number of different isotopes of a particular element present.
Example for Isotopes:
The table shows information about the Isotopes in a sample of rubidium
( 72 x 85 ) + ( 28 x 87 ) ÷ 100 = 85.6
Relative Atomic Mass = 85.6
Relative formula (molecular) mass
- The symbol for the relative molecular mass is Mr and it refers to the total mass of the molecule.
- To calculate the Mr of a substance, you have to add up the Relative Atomic Masses of all the atoms present in the formula