The number of atoms, molecules, formula units or ions in one gram atom, one gram molecule, one gram formula unit or one gram ion, respectively is called Avogadro’s number.

OR

The number of atoms, molecules, formula units or ions in one mole of the substance is called Avogadro’s number.

## Representation of Avogadro’s Number:

It is represented by **N**_{A}.

### Value of Avogadro’s Number:

Its value is **6.02 x 10**^{23}.

Examples:

- 1 gram of H = 1 gram atom
of H = 1 mole of H = 6.02 x 10
^{23}atoms of H

- 2 grams of H
_{2}= 1 gram molecule of H_{2}= 1 mole of H_{2}= 6.02 x 10^{23}molecules of H_{2}

- 58.5 grams of NaCl = 1 gram
formula mass of NaCl= 1 mole of NaCl = 6.02 x 10
^{23}formula units of NaCl

- 23 grams of Na
^{+1}= 1 gram ion of Na^{+1}= 1 mole of Na^{+1}= 6.02 x 10^{23}ions of Na^{+1}

Formulas, which can be used to calculate the number of atoms, molecules, formula units or ions in the given sample of a substance are given below: