Avogadro and the Mole

One mole of a material has a mass of M grams, where M is the molecular mass in atomic mass units, u. Oxygen has a molecular mass of 16, so 1 mole of Oxygen atoms has a mass of 16g, 2 moles has a mass of 32g and so on. An Oxygen molecule is made of two atoms so it has a molecular mass of 32g. This means 16g would be half a mole of Oxygen molecules.

where n is the number of moles, m is the mass and M is the molecular mass.

Avogadro suggested that one mole of any substance contains the same number of particles, he found this to be 6.02 x 10²³. This gives us a second way of calculating the number of moles

where N is the number of particles and N_A is the Avogadro constant.

N_A is the Avogadro Constant, N_A = 6.02 x 10²³ mol^-1