Mole-One mole of any species (atoms, molecules, ions or particles) is that quantity or number having a mass equal to its atomic or molecular mass in grams.

1 mole = 6.022 x 10²³ in number (atoms, molecules, ions or particles)

Significance of the mole

1. A mole gives the number of entities present i.e, 6.022 x 10²³ particles of the substance.

2. Mass of 1 mole is expressed as M grams.

3. Mass of 1 mole = mass of 6.022 x 10²³ atoms of the element.

E.g., 1 mole of O₂ = 6.022 x 10²³ atoms

2 x 16 = 32 g

6.022 x 2 x 10²³ = 1.2044 x 10⁴ atoms

1 mole of (compound) HCl = 6.022 x 10²³ atoms of H and Cl atoms

(1 + 35.5 = 36.5 g) = (6.022 x 10²³molecules of HCl)