| Definition: | quantity proportional to the number of elementary entities of a specified nature which are contained in a given sample of matter, the proportionality coefficient being the same for all samples NOTE 1 The elementary entities must be specified and may be of any kind: atoms, molecules, ions, electrons, holes, other particles or quasi-particles, groups of particles, double bonds, etc. NOTE 2 The proportionality coefficient in the definition is the reciprocal of the Avogadro constant NA, thus N = nNA, where N is the number of elementary entities. NOTE 3 The term "amount of substance" is to be interpreted as a whole, not as a combination of two terms. However, the words “of substance” could be replaced by words to specify the substance concerned in any specific application, e.g. “amount of hydrogen chloride, HCl”. NOTE 4 Amount of substance is one of the seven base quantities in the International System of Quantities, ISQ, on which the International System of Units, SI, is based. The coherent SI unit of amount of substance is mole, symbol mol (see IEC 60050-112:2010, 112-02-09).
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