Home : Patterns : Relative Atomic Mass & Relative Formula Mass
The Relative Atomic Mass of a chemical element gives us an idea of how heavy it feels (the force it makes when gravity pulls on it). If you look at the periodic table you can find out the relative atomic masses of the elements.
The number at the top of the symbol is the Relative Atomic Mass (Ar ):
Most atoms exist in molecules. You can use the Relative Atom Masses of elements to work out the mass of the molecule they make up.
To work out the Relative Formula Mass you simply add up the Relative Atomic Masses of each atom in the molecule:
So sodium chloride (NaCl) has 1 sodium atom and 1 chlorine atom
and water (H2O) has 2 hydrogen atoms and 1 oxygen atom