1.18 understand the term mole as the Avogadro number of particles (atoms, molecules, formulae, ions or electrons) in a substance

The mole simply represents a number, just as a dozen represents the number 12.  The number of particles in a mole is called Avogadro’s Number.

Avogadro’s Number  =  6 x 1023  (= 600,000,000,000,000,000,000,000)

That’s a very big number. It has been estimated it is approximately the number of grains of sand in the Sahara Desert.

For example, one mole of ethane molecules (C2H6) contains two moles of carbon atoms and six moles of hydrogen atoms. Chemists count things like atoms, ions and electrons by the mole.

e.g.      How many Cl atoms are in 4.0 mol of Cl2?

Moles of Cl atoms = 4.0 mol x 2 (since Cl2) = 8.0 mol

Number of Cl atoms = 8.0 x 6 x 1023 = 4.8 x 1024 Cl atoms

It’s easy really!  If someone said, “How many apples in two dozen?”, you’d say 24 straight away. This is no different. The numbers are just more awkward, but the concept is straightforward.

Note:    You are not normally asked to do calculations with Avogadro’s number.  What is more important is to remember that MOLE RATIOS tell you the RATIOS of particles.