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Before the 2019 revision of the SI, the mole was defined as the amount of substance of a system that contains as many elementary entities as there are atoms in 12 grams of carbon-12 (the most common isotope of carbon). [19] The term gram-molecule was formerly used to mean one mole of molecules, and gram-atom for one mole of atoms. [15]
The SI system after 1983, but before the 2019 revision: Dependence of base unit definitions on other base units (for example, the metre is defined as the distance travelled by light in a specific fraction of a second), with the constants of nature and artefacts used to define them (such as the mass of the IPK for the kilogram).
The International System of Units, or SI, [1]: 123 is a decimal and metric system of units established in 1960 and periodically updated since then. The SI has an official status in most countries, including the United States , Canada , and the United Kingdom , although these three countries are among the handful of nations that, to various ...
Historically, the mole was defined as the amount of substance in 12 grams of the carbon-12 isotope.As a consequence, the mass of one mole of a chemical compound, in grams, is numerically equal (for all practical purposes) to the mass of one molecule or formula unit of the compound, in daltons, and the molar mass of an isotope in grams per mole is approximately equal to the mass number ...
The SI system after the 2019 definition: Base units as defined in terms of physical constants and other base units. Here, means is used in the definition of . The SI system after 1983, but before the 2019 redefinition: Base unit definitions in terms of other base units (for example, the metre is defined as the distance travelled by light in a specific fraction of a second), with the constants ...
The Avogadro constant, commonly denoted N A [1] or L, [2] is an SI defining constant with an exact value of 6.022 140 76 × 10 23 mol −1 (reciprocal moles). [3] [4] It is this defined number of constituent particles (usually molecules, atoms, ions, or ion pairs—in general, entities) per mole and used as a normalization factor in relating the amount of substance, n(X), in a sample of a ...
Since the 2019 revision of the SI, [1] the Faraday constant has an exactly defined value, the product of the elementary charge (e, in coulombs) and the Avogadro constant (N A, in reciprocal moles): F = e × N A = 1.602 176 634 × 10 −19 C × 6.022 140 76 × 10 23 mol −1 = 9.648 533 212 331 001 84 × 10 4 C⋅mol −1.
With this approach, the Avogadro constant would not only be fixed, but so too would the atomic mass of 28 Si. As such, the definition of the kilogram would be decoupled from 12 C and the kilogram would instead be defined as 1000 / 27.976 926 5325 ⋅ 6.022 141 79 × 10 23 atoms of 28 Si (≈ 35.743 740 43 fixed moles of 28 Si atoms).