Avogadro constant
Proper noun
Meaning
Avogadro constant
(chemistry, physics) The number of atoms present in 12 grams of isotopically pure carbon-12, being 6.02214076 × 10. By definition, the number of elementary entities (atoms or molecules) comprising one mole of a given substance.
Synonyms: Avogadro's constant, Avogadro's number
Examples
All silicon-based approaches would fix the Avogadro constant but vary in the details of the definition of the kilogram.
By fixing the Avogadro constant, the practical effect of this proposal would be that the uncertainty in the mass of a 12 C atom—and the magnitude of the kilogram—could be no better than the current 50 ppb uncertainty in the Planck constant.
As described in Carbon 12 above, this method would define the magnitude of the kilogram in terms of a certain number of 12 C atoms by fixing the Avogadro constant; the silicon sphere would be the practical realization.
Avogadro's number, and its definition, was deprecated in favor of the Avogadro constant and its definition.
As of the 2006 CODATA recommended values, the relative uncertainty in determinations of the Avogadro constant by the X-ray crystal density method is main, about two and a half times higher than that of the electron mass method.
As with a definition based upon carbon 12, the Avogadro constant would also have been fixed.