A new definition of the mole has arrived

https://iupac.org/new-definition-mole-arrived/ , 8 January 2018

IUPAC is recommending a new definition of the mole based on a specified number of elementary entities [Roberto Marquardt, Juris Meija, Zoltán Mester, Marcy Towns, Ron Weir, Richard Davis and Jürgen Stohner, “Definition of the mole
 (IUPAC Recommendation 2017)”, Pure Appl. Chem. 90(1), pp. 175-180 (2018), https://doi.org/10.1515/pac-2017-0106]:

The mole, symbol mol, is the SI unit of amount of substance. One mole contains exactly 6.022 140 76 × 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, N_A, when expressed in mol⁻¹, and is called the Avogadro number.

After an extensive consultation with the chemistry community, and following a review and critical evaluation of the literature the new definition comes in advance of the anticipated revision of the International System of Units (SI).

The new SI will be linking all seven base units to fundamental physical constants.Revised definitions of the kilogram, ampere, kelvin and mole are expected to come into force on World Metrology Day, 20 May 2019.

Z tlačovej správy IUPAC pre vás vybral Milan Drábik, predseda SNK IUPAC.