In chemistry, the unit “mole” is used in many places, and is an important tool when working with quantities. If we express the R.A.M. of any element in grams, this must contain the same number of atoms (6.022 x 10^{23}). The RA.M. of any element expressed in grams contains I mol of that element. This is called the molar mass, and is given the symbol M. The mole is widely used in chemistry as a convenient way to express amounts of reactants and products of chemical reactions.

For example, Beryllium (R.A.M. = 9); Argon (R.A.M. = 40). Therefore 9 g of Beryllium and 40 g of Argon contains the same number of atoms (6.022 x 10^{23}). Another example, Silicon (R.A.M. = 28), therefore the molar mass of Si is 28 g mol-‘ and is represented by M (Si).

Molecules: The mole concept is equally applicable to molecules. We introduce the relative molecular mass (R.M.M.) which is expressed in grams and represents one mole of the element or compound (i.e. 6.022 x 10^{23}) molecules).