Mole Concept and Avogadro’s Constant

Mass of an atom or a molecule is an important property. However, while discussing the quantitative aspects of a chemical reaction, the number of reacting atoms or molecules is more significant than their masses.

Mole

A mole is the amount of a substance that contains as many elementary entities (atoms, molecules or other particles) as there are atoms in exactly 0.012 kg or 12 g of the carbon-12 isotope.

One mole always contains the same number of entities, no matter what the substance is. Thus mole is a number unit for dealing with elementary entities such as atoms, molecules, formula units, electrons, etc., just as dozen is a number unit for dealing with bananas or oranges.

Avogadro’s Constant

A mole of a substance is that amount which contains as many elementary entities as there are atoms in exactly 0.012 kilogram or 12 gram of the carbon-12 isotope. Now the question arises how many atoms are there in exactly 12 g of carbon-12. This number is determined experimentally and its currently accepted value is 6.022045 × 10²³. This number is known as Avogadro’s constant.

N_A = 6.022 × 10²³ mol^-1

Molar Mass

The molar mass is defined as the mass (in grams) of 1 mole of a substance. Similarly, a mole of any substance would contain 6.022 × 10²³ particles or elementary entities.