Avogadro’s number: 6.02×1023

(Ar) Relative Atomic Mass

mass of the protons and Neutrons
Mean mass of 1 atom of the element
1/12 the mass of atom of Carbon-12

(Mr) Molecular mass

The sum of the Ar for all of the atoms in the formula
Mean mass of the molecule
1/12 the mass of atom of carbon-12

The Mole

The weight of the relative atomic mass of any element e.g. carbon-12 = 12.00g (1 mole)

To weigh one atom of an element divide the moles in grams by Avogadro’s number

e.g. 1 mole of carbon-12 = 12g

6.02×1023

Examples

a) 1 mole of hydrogen = 1.0g
b) Mass of 1 atom of H = 12g
6.02×1023

a) 1 mole of Copper = 24.3g
b) Mass of 1 atom of Cu = 3g
6.02×1023

a) 1 mole of Hydrogen Molecule = 2.0g
b) Mass of 1 atom of H2 = 0g
6.02×1023

a) 1 mole of Calcium Nitrate= 64.1g
b) Mass of 1 atom of Ca(NO3)2 = 1g
6.02×1023