## Avogadro constant |

the

**avogadro constant**, usually denoted by*n*_{a}^{[1]}or*l*^{[2]}is the factor that, multiplied by the in a sample, measured inamount of substance , gives the number ofmoles (usuallyconstituent particles ,molecules oratoms ) in that sample. its unit is the reciprocal of mole, and it is defined asions *n*_{a}= 6.02214076×10^{23}mol^{−1}.^{[3]}^{[1]}^{[4]}^{[5]}^{[6]}it is named after the italian scientist .amedeo avogadro ^{[7]}the numeric value of the avogadro constant, a dimensionless number, is called the

**avogadro number**, sometimes denoted*n*^{[8]}^{[9]}or*n*_{0},^{[10]}^{[11]}which is thus the number of particles that are contained in one mole, the unit of amount of substance, exactly 6.02214076×10international (si) ^{23}.^{[4]}^{[1]}the value of the avogadro constant was chosen so that the mass of one mole of a

, inchemical compound , is numerically equal (for all practical purposes) to the average mass of one molecule of the compound, ingrams ; one dalton being 1/12 of the mass of onedaltons (universal atomic mass units) atom, which is approximately the mass of onecarbon-12 (nucleon orproton ). for example, the average mass of one molecule ofneutron is about 18.0153 daltons, and one mole of water (water *n*molecules) is about 18.0153 grams. thus, the avogadro constant*n*_{a}is the that relates theproportionality factor of a substance to the averagemolar mass of one molecule, and the avogadro number is also the approximate number of nucleons in one gram of ordinarymass .matter ^{[12]}the avogadro constant also relates the

of a substance to the average volume nominally occupied by one of its particles, when both are expressed in the same units of volume. for example, since the molar volume of water in ordinary conditions is about 18molar volume /mol, the volume occupied by one molecule of water is about 18/6.022×10ml ^{−23}ml, or about 30Å ^{3}(cubic ). for aangstroms substance, it similarly relates its molar volume (in ml/mol), the volume of the repeatingcrystaline of the crystals (in ml), and the number of molecules in that cell.unit cell the avogadro number (or constant) has been defined in many different ways through its long history. its approximate value was first determined, indirectly, by

in 1865.josef loschmidt ^{[13]}(avogadro's number is closely related to the , and the two concepts are sometimes confused.) it was initially defined byloschmidt constant as the number of atoms in 16 grams ofjean perrin .oxygen ^{[7]}it was later redefined in the 14th conference of the (bipm) as the number of atoms in 12 grams of the isotopeinternational bureau of weights and measures (carbon-12 ^{12}c).^{[14]}in each case, the mole was defined as the quantity of a substance that contained the same number of atoms as those reference samples. in particular, when carbon-12 was the reference, one mole of carbon-12 was exactly 12 grams of the element.these definitions meant that the value of the avogadro number depended on the experimentally determined value of the mass (in grams) of one atom of those elements, and therefore it was known only to a limited number of decimal digits. however, in its 26th conference, the bipm adopted a different approach: effective 20 may 2019, it defined the avogadro number as the exact integer

*n*= 6.02214076×10^{23}, and redefined the mole as the amount of a substance under consideration that contains*n*constituent particles of the substance. under the new definition, the mass of one mole of any substance (including hydrogen, carbon-12, and oxygen-16) is*n*times the average mass of one of its constituent particles—a physical quantity whose precise value has to be determined experimentally for each substance.- history
- the avogadro constant in other unit systems
- connection to other constants
- see also
- references
- external links

The **Avogadro constant**, usually denoted by *N*_{A}^{[1]} or *L*^{[2]} is the factor that, multiplied by the *N*_{A} = 6.02214076×10^{23} mol^{−1}.^{[3]}^{[1]}^{[4]}^{[5]}^{[6]} It is named after the Italian scientist ^{[7]}

The numeric value of the Avogadro constant, a dimensionless number, is called the **Avogadro number**, sometimes denoted *N*^{[8]}^{[9]} or *N*_{0},^{[10]}^{[11]} which is thus the number of particles that are contained in one mole, the ^{23}.^{[4]}^{[1]}

The value of the Avogadro constant was chosen so that the mass of one mole of a *N* molecules) is about 18.0153 grams. Thus, the Avogadro constant *N*_{A} is the ^{[12]}

The Avogadro constant also relates the ^{−23} mL, or about 30 ^{3} (cubic

The Avogadro number (or constant) has been defined in many different ways through its long history. Its approximate value was first determined, indirectly, by ^{[13]} (Avogadro's number is closely related to the ^{[7]} It was later redefined in the 14th conference of the ^{12}C).^{[14]} In each case, the mole was defined as the quantity of a substance that contained the same number of atoms as those reference samples. In particular, when carbon-12 was the reference, one mole of carbon-12 was exactly 12 grams of the element.

These definitions meant that the value of the Avogadro number depended on the experimentally determined value of the mass (in grams) of one atom of those elements, and therefore it was known only to a limited number of decimal digits. However, in its 26th Conference, the BIPM adopted a different approach: effective 20 May 2019, it defined the Avogadro number as the exact integer *N* = 6.02214076×10^{23}, and redefined the mole as the amount of a substance under consideration that contains *N* constituent particles of the substance. Under the new definition, the mass of one mole of any substance (including hydrogen, carbon-12, and oxygen-16) is *N* times the average mass of one of its constituent particles—a physical quantity whose precise value has to be determined experimentally for each substance.