SI base unit: mole (mol)

The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 x 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, N_A, when expressed in the unit mol^–1 and is called the Avogadro number.

The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.

This definition implies the exact relation N_A = 6.022 140 76 x 10²³ mol^–1. Inverting this relation gives an exact expression for the mole in terms of the defining constant N_A:

The effect of this definition is that the mole is the amount of substance of a system that contains 6.022 140 76 x 10²³ specified elementary entities.

See: