Avogadro's Number

In chemistry and physics, Avogadro's number — is the number of particles, usually atoms or molecules, contained in 1 mole of substance. Thus, it is the proportionality factor that relates the molar mass of constituents to the mass of a sample. Avogadro's number is often denoted by the symbol NA or L. Also known as Avogadro's constant.

This quantity is named after the Italian scientist, physicist, and chemist Amedeo Avogadro. He established an important physical law — Avogadro's law, which is the basis for determining atomic and molecular masses. Avogadro's number is the scaling factor between the macroscopic and microscopic (in the scale of atoms) representations of the surrounding world. As such, it provides a link between other physical constants and properties.

The precise value of Avogadro's number was first officially established in 2010 through experiments with two silicon-28 spheres. According to the data obtained, the value was 6.02214084(18)×1023 mole−1. These data were repeatedly verified, and the constant's value changed. As of 2016, Avogadro's number is still a measured unit, not taken by default. The latest recommended value — NA = 6,022 140 82(11)·1023 mole−1.