In chemistry, the Avogadro constant, commonly denoted ,

The name Avogadro's number was coined in 1909 by the physicist Jean Perrin, who defined it as the number of molecules in exactly 32 grams of oxygen gas. The Avogadro Project used this technique to measure the unit cell dimensions of extremely pure single-crystal spheres of silicon-28, with the goal of a more accurate silicon-based definition of the Avogadro constant.

SI definition of 1971

In 1971, in its 14th conference, the International Bureau of Weights and Measures (BIPM) decided to regard the amount of substance as an independent dimension of measurement, with the mole as its base unit in the International System of Units (SI).

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  • 1996 definition of the Avogadro constant from the IUPAC Compendium of Chemical Terminology ("Gold Book")
  • Some Notes on Avogadro's Number, (historical notes)
  • An Exact Value for Avogadro's Number – American Scientist
  • Avogadro and molar Planck constants for the redefinition of the kilogram
  • Scanned version of "Two hypothesis of Avogadro", 1811 Avogadro's article, on BibNum