# Avogadro’s number: Definition, Example and Relation with Mole

In chemistry, we deal with substances which are composed of atoms, molecules or formula units. The counting of these particles is not possible for the chemists.the concept of Avogadro’s number facilitated the counting of particles contained in the given mass of a substance. **Avogadro’s Number **is a collection of 6.02 x 10^{23} particles.

It is represented by symbol ‘N_{A}’. Hence, the 6.02 x 10^{23} number of atoms, molecules or formula units is called Avogadro’s number that is equivalent to one ‘mole’ of respective substance. In simple words 6.02 x 10^{23} particles are equal to one mole as twelve eggs are equal to one dozen.

To understand **the relation between the Avogadro’s number and the mole **of a substance let us consider a few examples.

- 02 x 10
^{23}atoms of carbon are equivalent to one mole of carbon. - 02 x 10
^{23}molecules of H_{2}O are equivalent to one mole of water. - 02 x 10
^{23 }formula units of NaCl are equivalent to one mole of sodium chloride.

Thus, 6.02 x 10^{23 }atoms of elements or 6.02 x 10^{23 }molecules of molecular substance or 6.02 x 10^{23 }formula units of ionic compounds are equivalent to 1 mole.

For further explanation about number of atoms in molecular compounds or number of ions in ionic compounds let us discuss two examples:

- One molecule of water is made up of 2 atoms of hydrogen and 1 atom of oxygen, hence 2 x 6.02 x 10
^{23 }atoms of hydrogen and 6.02 x 10^{23 }atoms of oxygen constitute one mole of water. - One formula unit of sodium chloride consists of one sodium ion and one chloride ion.so there are 6.02 x 10
^{23 }number of Na^{+ }ions and 6.02 x 10^{23 }Cl^{–}ions in one mole of sodium chloride. Thus, the total number of ions in 1 mole of NaCl is 12.04 x 10^{23}or 1.204 x 10^{24}.