Avogadro constant

Avogadro constant

The Avogadro constant, symbolized as N_A or L, is a fundamental physical constant that defines the number of constituent particles, usually atoms or molecules, that are contained in one mole of a given substance. The Avogadro constant is named after the Italian scientist Amedeo Avogadro, who, in 1811, hypothesized that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. This principle is known as Avogadro's law.

Definition

The Avogadro constant is defined as the number of atoms in exactly 12 grams of carbon-12 (^12C), the isotope of carbon with a relative atomic mass of 12. This definition ties the Avogadro constant to the kilogram, one of the seven base units of the International System of Units (SI). As of the redefinition of SI units in 2019, the Avogadro constant has been defined with an exact value of 6.02214076×10^23 mol^−1.

Measurement

The value of the Avogadro constant has been determined through various experimental methods. One of the most precise methods involves the use of X-ray crystallography to measure the spacing between atoms in a silicon crystal. By knowing the volume of the crystal and the spacing between atoms, the number of atoms in a given mass can be calculated, thus providing an estimate of the Avogadro constant.

Importance

The Avogadro constant plays a crucial role in chemistry and physics, serving as a bridge between the microscopic world of atoms and molecules and the macroscopic world of grams and liters. It allows scientists to convert between the number of particles and the amount of substance in moles, facilitating calculations involving the stoichiometry of chemical reactions, the determination of gas laws, and the calculation of molecular weights.

Related Constants

The Avogadro constant is closely related to other fundamental constants, such as the Boltzmann constant (k) and the Faraday constant (F). The Boltzmann constant relates the average kinetic energy of particles in a gas to the temperature of the gas, while the Faraday constant represents the charge of one mole of electrons. Together, these constants help describe the behavior of substances at the atomic and molecular levels.

See Also

• Mole (unit)
• Stoichiometry
• International System of Units
• Atomic mass unit

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Avogadro constant gallery

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  Amadeo Avogadro

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  Mole carbon-12 diagram

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  Jean Perrin 1926

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  Johann Josef Loschmidt portrait plaque