Difference between revisions of "Unified atomic mass unit"

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Revision as of 18:29, 14 July 2009

Unified atomic mass unit

A non-SI unit of mass defined as one twelfth of the mass of one atom of 12C in its ground state and equal to 1.660 5402(10) x 10-27 kg.

The term atomic mass unit is deprecated.

Note: The term atomic mass unit (amu) is ambiguous as 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.

Considered between 2004 and 2006 but not included in the 2006 PAC submission
This is an unofficial draft definition presented for information and comment.

Recommended terms | Full list of terms

Orange Book entry

Orange Book


IUPAC. Analytical Division. Compendium of Analytical Nomenclature (the Orange Book). Definitive Rules, 1979.

Unified atomic mass unit

This unit (u) is based on the standard that the mass of 12C is exactly 12 u. The older symbol, amu, using the standard based on the mass of 16O is no longer recommended. In biochemistry the term dalton, symbol Da, is sometimes used but is not here recommended.

IUPAC 1997 Orange Book Chapter 12
Index of Orange Book Terms

Gold Book entry

Gold Book


IUPAC. Compendium of Chemical Terminology, 2nd ed. (the Gold Book). Compiled by A. D. McNaught and A.Wilkinson. Blackwell Scientific Publications, Oxford (1997).

Unified atomic mass unit

unified atomic mass unit

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 &61; 1.660 5402(10) x 10-27 kg.


IUPAC Gold Book
Index of Gold Book Terms

See also

External links