A mole of a substance is the amount that contains the same number of units (atoms, molecules or ions) as the number of carbon atoms in 12 grams of Carbon-12.
- We know that atom is an extremely small particle.
- The mass of an individual atom is a very small quantity and is not feasible for calculation.
- It is impossible to weight individual atoms or even small groups of atoms directly.
- Therefore, the concept of mole is used. One mole of a substance is the relative atomic/molecular mass expressed in grams.