In chemistry, the term mole represents a pile or mass of atoms, molecules, ions or electrons. Just as common man measures quantity in terms of kilograms or dozens, a chemical scientist deals with a 'mole' of atoms, molecules, ions or electrons.
Mole is defined as the amount of a substance, which contains the same number of chemical units (atoms, molecules, ions or electrons) as there are atoms in exactly 12 grams of pure carbon-12. A mole represents a collection of 6.023 x 1023 ( Avogadro's number) chemical units. Thus a mole represents the quantity of material, which contains one Avogadro's number of chemical units of any substance. The unit of mole is denoted as 'mol'.
One mole of hydrogen atoms = 6.023 x 1023 atoms of hydrogen
One mole of hydrogen molecules = 6.023 x 1023 molecule of hydrogen
One mole of electrons = 6.023 x 1023 electrons
One mole of sodium ions (Na+) = 6.023 x 1023 Na+ ions
It can be thus concluded that,
One mole of atoms = 6.023 x 1023 atoms = Gram atomic mass of the element.
One mole of molecules = 6.023 x 1023 molecules = Gram molecular mass.
The volume occupied by one mole of any substance is called its molar volume. It is denoted by Vm. Molar volume of the substance depends on temperature and pressure. One mole of all gaseous substances at 273 K and 1 atm pressure occupies a volume equal to 22.4 litre or 22,400 mL. The unit of molar volume is litre per mol or millilitre per mol.
The various relationships of mole can be summarized as follows:
Fig: 1.6 - Mole relationships