In a chemical reaction equation,it is more convenient to use quantity of substance in number of its molecules or atoms rather than their masses,so we use a new unit called MOLE.
If we weigh an element equal to its atomic mass in grams,then it contains 6.022×10^23 atoms of the element.The gram atomic mass of the element as well as 6.022×10^23 atoms of the element,both represent 1 mole of element.1 mole of any species (atoms,molecules,ions) is equal to its atomic mass or molecular mass in grams.
No. of particles(atoms,molecules,ions) in 1 mole = 6.022×10^23
This number is called as AVOGADRO’S CONSTANT
1 mole of atom = 6.022×10^23atoms