mole

SI base unit

Name	Symbol	Quantity
mole	mol	amount of substance
The mole, symbol mol, is the SI base unit of amount of substance. One mole contains exactly 6.022 140 76 × 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.
Definition
$1 \mspace{4mu} \text{mol} = 6.022 \mspace{4mu} 140 \mspace{4mu} 76 \times10^{23} \mspace{6mu} {N_A}^{-1}$

Amount of substance

The definition of the mole implies the exact relation:

$N_A \mspace{4mu} = 6.022 \mspace{4mu} 140 \mspace {4mu} 76 \times 10^{23} \ \text{mol}^{-1}$

Inverting this relation gives an exact expression for the mole in terms of the defining constant N_A :

$1 \mspace{4mu} \text{mol} \mspace{10mu} = \dfrac{6.022 \mspace{4mu} 140 \mspace{4mu} 76 \times 10^{23}}{N_A}$

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

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.