The Avogadro constant, NA = 6.022 140 76 x 10E23 mol-1, is a proportionality constant between the quantity amount of substance (n, with unit mole) and the quantity for counting entities (N with unit one, symbol 1), N=N_A.n.
Notes: - In the revision of the International System of Units (SI) of 2019 the Avogadro constant became one of the seven defining constants with the exact value 6.022 140 76 x 10E23 mol-1.
- The Avogadro number is the exact numerical value of the Avogadro constant, 6.022 140 76 x 10E23
- While the symbol NA is used to honour Amedeo Avogadro, the symbol L is used in honour of Josef Loschmidt.
Sources:
BIPM, Le Système international d’unités (SI), SI Brochure, 9e ed. (2019), p. 17 (https://www.bipm.org/fr/publications/si-brochure/)
BIPM, The International System of Units, SI Brochure, 9th ed. (2019), p. 129 (https://www.bipm.org/en/publications/si-brochure/)
Green Book, 3rd ed. (https://doi.org/10.1039/9781847557889)