Avogadro constant

The Avogadro constant N_{\text{A}} indicates how many particles (e.g. atoms of an element or molecules of a chemical compound) are contained in one mole. It is named after Amedeo Avogadro. The value of the Avogadro constant is

{\displaystyle N_{\mathrm {A} }=6{,}022\,140\,76\cdot 10^{23}\,\,\mathrm {mol} ^{-1}\,\,},

which is a good 602 quadrillion particles per mole. Generally applies

{\displaystyle N=n\cdot N_{\mathrm {A} }\,\,},

where N is the number of particles and n is the amount of substance.

The unitless number 6.02214076e23 is called the Avogadro number. It was fixed at this value as part of the revision of the International System of Units in 2019 and has since defined the unit of measurement "mole". The number was chosen so that 1 mole of particles, each with a mass of X atomic mass units (u), would have a total mass as close as possible to X grams (g).

Until 2019, the mole was defined by the microscopic and macroscopic mass scales: the amount of substance of a total mass X g of particles of particle mass X u was defined as 1 mole. The Avogadro constant was defined as the number of particles in 1 mol and thus a natural constant to be determined experimentally.

Applications

The Avogadro constant NA is used to convert between quantities that refer to numbers of particles and those that refer to quantities of substances.

{\displaystyle N=N_{\text{A}}\cdot n}

{\displaystyle N\colon }number of particles

{\displaystyle n\colon }amount of substance

Relationships with other constants:

  • {\displaystyle R=N_{\text{A}}\cdot k_{\text{B}}}

R\colon Universal gas constant

Boltzmann constant{\displaystyle k_{\text{B}}\colon }

  • {\displaystyle F=N_{\text{A}}\cdot e}

F\colon Faraday constant

elementary charge{\displaystyle e\colon }

  • {\displaystyle M=N_{\text{A}}\cdot m_{\text{a}}}

{\displaystyle M\colon }Molar mass

atomic mass{\displaystyle m_{\text{a}}\colon }

The relationship between mass, amount of substance, volume and number of particlesZoom
The relationship between mass, amount of substance, volume and number of particles


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