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

In chemistry, we deal with substances that are composed of atoms, molecules, or formula units. The counting of these particles is not possible for 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 the symbol ‘N_{A}’. Hence, the 6.02 x 10^{23} number of atoms, molecules, or formula units is called Avogadro’s number which is equivalent to one ‘mole’ of the respective substance. In simple words, 6.02 x 10^{23} particles are equal to one mole and twelve eggs are equal to one dozen.

To understand the relation between 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 a molecular substance, or 6.02 x 10^{23 }formula units of ionic compounds are equivalent to 1 mole.

For further explanation about the number of atoms in molecular compounds or the 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 }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}.