https://doi.org/10.1351/goldbook.M03980
The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly \(\pu{6.02214076E23}\) elementary entities. This number is the fixed numerical value of the Avogadro constant, \(N_{\rm{A}}\), when expressed in the unit \(\pu{mol-1}\) 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.Note: The formulation of this definition was agreed upon by the 26th CGPM in November 2018 with effect from 20 May 2019.