C2 3.2 Masses of atoms and moles

• Atoms are much too small to weigh and so we use relative atomic masses (Ar) in calculations. Relative atomic masses are often shown in periodic tables. In the laboratory we usuall weigh substances in grams. The relative atomic mass of an element in grams is called one mole of atoms of the element.

Relative atomic mass

We use ana tom of 126C as a standard atom and compare the masses of all other…