The molecular weight of a substance expressed in gm is referred to as the gm-molecular weight or the gm-molecule or simply a mole.
However, both gm-molecule and gm-atom can be represented by mole. The term mole of a substance may be defined as the weight in gms which contains the Avagadro number (6.023×1023) of molecules. The term mole may be used in any of the following:
1. 1 mole = 1 gm-molecule or 1 gm atom.
2. In the case of gases, 1 mole = 22.4 litres at N.T.P
3. 1 mole = Avogadro No. (6.023×1023) of molecules or atoms or ions or electrons and also one Faraday of electricity.
It is the number of molecules present in one gram-molecule of any substance. It also represents the number of atoms in one gram atom of any substance. So, Avagadro Number also denotes the number of molecules represents in 22.4 litres of any gas at N.T.P.
Avagadro Number is also defined as the number of ions in one gm-ion of a monovalent atom or a radical. It is denoted by the letter ‘N’ and its value is 6.023×1023. 1 Faraday of electricity (1 mole of electricity) is composed of 6.023×1023 electrons.
Example: 1 gm-molecule of H2 (2gms) and 1 gm-molecule of O2 (32 gms) through differ in weight, each of these masses contains Avogadro Number (6.023×1023) of molecules.