Difference between revisions of "Atomic mass unit"
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| − | The '''atomic mass unit''' (symbol: '''u'''), also called the '''dalton''' (symbol: '''Da'''), is a [[Unit of measurement|unit]] of [[mass]] used with the SI. The value of the atomic mass unit is a [[physical constant]] called the '''atomic mass constant''': the 2006 [[CODATA]] recommended value is {{nowrap|1.660 538 782(83){{e|−27}} kg}}.<ref>{{CODATA 2006|url=http://physics.nist.gov/cgi-bin/cuu/Value?u}}.</ref> | + | The '''atomic mass unit''' (symbol: '''u'''), also called the '''dalton''' (symbol: '''Da'''), is a [[Unit of measurement|unit]] of [[mass]] used with the SI. The value of the atomic mass unit is a [[physical constant]] called the '''atomic mass constant''' (symbol: '''''m''<sub>u</sub>'''): the 2006 [[CODATA]] recommended value is {{nowrap|1.660 538 782(83){{e|−27}} kg}}.<ref>{{CODATA 2006|url=http://physics.nist.gov/cgi-bin/cuu/Value?u}}.</ref> |
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| + | ==Definition and measurement== | ||
| + | The atomic mass constant is defined as one twelfth of the rest mass of an isolated atom of [[carbon-12]] in its nuclear and electronic ground state.<ref>{{GoldBookRef|title=atomic mass constant|file=A00497|accessdate=2010-07-16}}.</ref> An equivalent definition used to determine to value of the atomic mass constant is the [[molar mass constant]] divided by the [[Avogadro constant]]. | ||
| + | :''m''<sub>u</sub> = ''M''<sub>u</sub>/''N''<sub>A</sub> | ||
| + | As the molar mass constant has a defined value in the [[International System of Units]], the atomic mass constant is determined by the Avogadro constant. | ||
==References== | ==References== | ||
Revision as of 20:04, 15 July 2010
The atomic mass unit (symbol: u), also called the dalton (symbol: Da), is a unit of mass used with the SI. The value of the atomic mass unit is a physical constant called the atomic mass constant (symbol: mu): the 2006 CODATA recommended value is 1.660 538 782(83) × 10−27 kg.[1]
Definition and measurement
The atomic mass constant is defined as one twelfth of the rest mass of an isolated atom of carbon-12 in its nuclear and electronic ground state.[2] An equivalent definition used to determine to value of the atomic mass constant is the molar mass constant divided by the Avogadro constant.
- mu = Mu/NA
As the molar mass constant has a defined value in the International System of Units, the atomic mass constant is determined by the Avogadro constant.
References
- ↑ Mohr, Peter J.; Taylor, Barry N.; Newell, David B. CODATA Recommended Values of the Fundamental Physical Constants: 2006. Rev. Mod. Phys. 2008, 80 (2), 633–730. doi:10.1103/RevModPhys.80.633, <http://physics.nist.gov/cuu/Constants/codata.pdf>. Direct link to value.
- ↑ atomic mass constant, <http://goldbook.iupac.org/A00497.html> (accessed 16 July 2010), Compendium of Chemical Terminology Internet edition; International Union of Pure and Applied Chemistry (IUPAC).
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