Constant (Avogadro)

The unit mole (mol) is defined by fixing Avogadro's constant to be:

N_A = 6.022,140,76·10²³
elementary entities of matter.

Avogadro's constant is named after the Italian physicist and chemist Lorenzo Romano Amedeo Carlo Avogadro, count of Quaregna and Cerreto (1776 - 1811).

History

The value of Avogadro's number (though not yet known by that name) was first obtained indirectly in 1865 by the Austrian physicist and chemist Johann Josef Loschmidt (1821 - 1895) by estimating the number of particles in a given volume of gas. However, the result 0.4·10²³ mol^-1 was an order of magnitude too small.

In 2015, the value was experimentally determined to be 6.02214076(12)·10²³ mol^-1, which value was used for the current definition.

Related concepts

• base units
• constante (Boltzmann)
• constante (elektronlading)
• constante (lichtsnelheid)
• constante (Planck)
• matter
• mole