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Dalton (unit) AI simulator
(@Dalton (unit)_simulator)
Hub AI
Dalton (unit) AI simulator
(@Dalton (unit)_simulator)
Dalton (unit)
The dalton or unified atomic mass unit (symbols: Da or u, respectively) is a unit of mass defined as 1/12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. It is a non-SI unit accepted for use with SI. The word "unified" emphasizes that the definition was accepted by both IUPAP and IUPAC. The atomic mass constant, denoted mu, is an atomic-scale reference mass, defined identically, but it is not a unit of mass. Expressed in terms of ma(12C), the atomic mass of carbon-12: mu = ma(12C)/12 = 1 Da. The dalton's numerical value in terms of the fixed-h kilogram is an experimentally determined quantity that, along with its inherent uncertainty, is updated periodically. As listed in the 9th edition, version 3.02, of the SI Brochure, the 2022 CODATA recommended value of the atomic mass constant expressed in the SI base unit kilogram is:
mu = 1.66053906892(52)×10−27 kg.
The previous value given for the dalton (1 Da = 1 u = mu) was the 2018 CODATA recommended value:
1 Da = mu = 1.66053906660(50)×10−27 kg.
This was the value used in the calculation of g/Da, the traditional definition of the Avogadro number. This resulted in the value g/Da = 6.022 140 762 081 123 . . . × 1023, which was then rounded to 9 significant figures and fixed at exactly that value for the 2019 redefinition of the mole.
The value serves as a conversion factor of mass from daltons to kilograms, which can easily be converted to grams and other metric units of mass. The 2019 revision of the SI redefined the kilogram by fixing the value of the Planck constant (h), improving the precision of the atomic mass constant expressed in SI units by anchoring it to fixed physical constants. Although the dalton remains defined via carbon-12, the revision enhances traceability and accuracy in atomic mass measurements.
The mole is a unit of amount of substance used in chemistry and physics, such that the mass of one mole of a substance expressed in grams (i.e., the molar mass in g/mol or kg/kmol) is numerically equal to the average mass of an elementary entity of the substance (atom, molecule, or formula unit) expressed in daltons. For example, the average mass of one molecule of water is about 18.0153 Da, and the mass of one mole of water is about 18.0153 g. A protein whose molecule has an average mass of 64 kDa would have a molar mass of 64 kg/mol. However, while this equality can be assumed for practical purposes, it is only approximate, because of the 2019 redefinition of the mole.
The dalton is commonly used in physics and chemistry to express the mass of atomic-scale objects, such as atoms, molecules, and elementary particles, both for discrete instances and multiple types of ensemble averages. For example, an atom of helium-4 has a mass of 4.0026 Da. This is an intrinsic property of the isotope and all helium-4 atoms have the same mass. Acetylsalicylic acid (aspirin), C
9H
8O
4, has an average mass of about 180.157 Da. However, there are no acetylsalicylic acid molecules with this mass. The two most common masses of individual acetylsalicylic acid molecules are 180.0423 Da, having the most common isotopes, and 181.0456 Da, in which one carbon is carbon-13.
Dalton (unit)
The dalton or unified atomic mass unit (symbols: Da or u, respectively) is a unit of mass defined as 1/12 of the mass of an unbound neutral atom of carbon-12 in its nuclear and electronic ground state and at rest. It is a non-SI unit accepted for use with SI. The word "unified" emphasizes that the definition was accepted by both IUPAP and IUPAC. The atomic mass constant, denoted mu, is an atomic-scale reference mass, defined identically, but it is not a unit of mass. Expressed in terms of ma(12C), the atomic mass of carbon-12: mu = ma(12C)/12 = 1 Da. The dalton's numerical value in terms of the fixed-h kilogram is an experimentally determined quantity that, along with its inherent uncertainty, is updated periodically. As listed in the 9th edition, version 3.02, of the SI Brochure, the 2022 CODATA recommended value of the atomic mass constant expressed in the SI base unit kilogram is:
mu = 1.66053906892(52)×10−27 kg.
The previous value given for the dalton (1 Da = 1 u = mu) was the 2018 CODATA recommended value:
1 Da = mu = 1.66053906660(50)×10−27 kg.
This was the value used in the calculation of g/Da, the traditional definition of the Avogadro number. This resulted in the value g/Da = 6.022 140 762 081 123 . . . × 1023, which was then rounded to 9 significant figures and fixed at exactly that value for the 2019 redefinition of the mole.
The value serves as a conversion factor of mass from daltons to kilograms, which can easily be converted to grams and other metric units of mass. The 2019 revision of the SI redefined the kilogram by fixing the value of the Planck constant (h), improving the precision of the atomic mass constant expressed in SI units by anchoring it to fixed physical constants. Although the dalton remains defined via carbon-12, the revision enhances traceability and accuracy in atomic mass measurements.
The mole is a unit of amount of substance used in chemistry and physics, such that the mass of one mole of a substance expressed in grams (i.e., the molar mass in g/mol or kg/kmol) is numerically equal to the average mass of an elementary entity of the substance (atom, molecule, or formula unit) expressed in daltons. For example, the average mass of one molecule of water is about 18.0153 Da, and the mass of one mole of water is about 18.0153 g. A protein whose molecule has an average mass of 64 kDa would have a molar mass of 64 kg/mol. However, while this equality can be assumed for practical purposes, it is only approximate, because of the 2019 redefinition of the mole.
The dalton is commonly used in physics and chemistry to express the mass of atomic-scale objects, such as atoms, molecules, and elementary particles, both for discrete instances and multiple types of ensemble averages. For example, an atom of helium-4 has a mass of 4.0026 Da. This is an intrinsic property of the isotope and all helium-4 atoms have the same mass. Acetylsalicylic acid (aspirin), C
9H
8O
4, has an average mass of about 180.157 Da. However, there are no acetylsalicylic acid molecules with this mass. The two most common masses of individual acetylsalicylic acid molecules are 180.0423 Da, having the most common isotopes, and 181.0456 Da, in which one carbon is carbon-13.