![]() Nier, "Evolution of the unified scale of atomic mass, 12C = 12u," Int. Also, important in this field is Avogadros. ![]() ![]() By definition, carbon-12 has an atomic mass of exactly 12. It is defined to be 1/12 of the mass of one atom of carbon-12 and in older works is also abbreviated as amu. Atomic weights and the international committee–a historical review Chemistry International 2004 The remainder is mostly carbon-13, with traces of carbon-14, an unstable isotope produced in nature.Non-SI unit of mass (equal to the atomic mass constant), defined as one twelfth of the mass of a carbon-12 atom in its ground state and used to express masses of atomic particles, u = 1.660 5402(10) x 10 -27 kg. Blackwell Scientific Publications, Oxford (1997). Compendium of Chemical Terminology, 2nd ed. In biochemistry the term dalton, symbol Da, is sometimes used but is not here recommended. The older symbol, amu, using the standard based on the mass of 16O is no longer recommended. This unit (u) is based on the standard that the mass of 12C is exactly 12 u. Compendium of Analytical Nomenclature (the Orange Book). ( )įrom Definitions of Terms Relating to Mass Spectrometry (IUPAC Recommendations 2013) DOI: 10.1351/PAC-REC-06-04-06 © IUPAC 2013. XML on-line corrected version: (2006-) created by M. Note: The abbreviation amu for atomic mass unit is deprecated it has been used to denote atomic masses measured relative to a single atom of 16O, or to the isotope-averaged mass of an oxygen atom, or to a single atom of 12C. Non-SI unit of mass defined as one-twelfth of the mass of one atom of 12< -27 kg where the digits in parentheses indicate the estimated uncertainty in the final two digits of the value.
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