We might all have come across the number 6.022140857 × 10^23 in our chemistry text books. It is called the Avogadro’s number in honor of the Italian scientist Avogadro. It was initially defined by Jean Baptiste Perrin. In simple terms, it is referred to as a ‘mole’. A mole or Avogadro’s number is simply used by the chemists to measure the amount of a substance or count the particles of matter – atoms and molecules. Today Avogadro’s number(6.022140857 × 10^23) has such a great importance that mole day is being celebrated every year by the chemists unofficially on 23rd October beginning from 6:02 AM to 6: 02 PM to make sense to Avogadro’s number.
We know that the nucleus of an atom makes up more than 99.9% of its mass. Electrons do not contribute anything to the mass of an atom which is measured in terms of atomic mass unit (amu). One amu is defined as 1/12th of the mass of one carbon atom (with 6 protons and 6 neutrons inside the nucleus). But as the chemists did not have a scale to measure different weights of different atoms, they wanted to find a relation between amu and grams. One amu was found to be equivalent to 1g/mol (or)
1 amu = 1/6.022140857× 10^23 grams.