Atomic mass units: Difference between revisions
(New page: The Atomic Mass Unit is defined as the twelfth part of the mass of a C<math>_{12}</math> atom. Hence, it is approximately equal to the mass of a proton. Elements are asigned masses in thes...) |
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The | {{numeric}} | ||
of the mass of a C<math>_{12}</math> atom. Hence, | The '''atomic mass unit''' (AMU) is defined as the twelfth part | ||
of the mass of a C<math>_{12}</math> atom. | |||
Its value (in SI units, | |||
[http://physics.nist.gov/cgi-bin/cuu/Value?tukg|search_for=atomic+mass+unit CODATA] value) is | |||
:<math>1.66054\times10^{-27} </math> kilograms | |||
Hence, | |||
it is approximately equal to the mass of a proton. | it is approximately equal to the mass of a proton. | ||
Elements are | Elements are assigned masses in these units which are | ||
not integer numbers. This is because | not integer numbers. This is because | ||
neutrons and protons have slightly different masses, | neutrons and protons have slightly different masses, | ||
because nuclear binding forces cause the total mass | because nuclear binding forces cause the total mass | ||
of a | of a nucleus to be less than that of the sum of | ||
its constituents, and, mainly, because of the | its constituents, and, mainly, because of the | ||
appearance of natural isotopes. Thus, Potassium | appearance of natural isotopes. Thus, Potassium | ||
| Line 12: | Line 18: | ||
isotopes. | isotopes. | ||
Here is a list of masses of elements and compounds in | Here is a list of masses of elements and compounds in atomic mass units: | ||
{| border="1" | |||
{| | |||
|- | |- | ||
| Compound/element || mass in amu | | Compound/element || mass in amu | ||
|- | |- | ||
| Ar || 39. | | Ar ([[argon]])|| 39.948 | ||
|- | |||
| C || 12.0107 | |||
|- | |||
| =CH || 13.01864 | |||
|- | |||
| -CH<sub>2</sub>- || 14.02658 | |||
|- | |||
| -CH<sub>3</sub> || 15.03452 | |||
|- | |||
| Xe || 131.293 | |||
|- | |- | ||
| | | CO<sub>2</sub> ([[carbon dioxide]])|| 44.0095 | ||
|- | |- | ||
| | | H || 1.00794 | ||
|- | |- | ||
| | | H<sub>2</sub>O ([[water]]) || 18.02 | ||
|- | |- | ||
| | | N<sub>2</sub> ([[nitrogen]])|| 28.01 | ||
|} | |} | ||
Note that sometimes the atomic mass unit is also known as the '''Dalton''' ('''Da'''), especially when dealing with macromolecules such as [[proteins]]. | |||
==References== | |||
#[http://www.iupac.org/reports/periodic_table/index.html IUPAC Periodic Table] | |||
[[Category: Physical constants]] | |||
Latest revision as of 17:57, 29 October 2007
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This page contains numerical values and/or equations. If you intend to use ANY of the numbers or equations found in SklogWiki in any way, you MUST take them from the original published article or book, and cite the relevant source accordingly. |
The atomic mass unit (AMU) is defined as the twelfth part of the mass of a C atom. Its value (in SI units, CODATA value) is
- kilograms
Hence, it is approximately equal to the mass of a proton. Elements are assigned masses in these units which are not integer numbers. This is because neutrons and protons have slightly different masses, because nuclear binding forces cause the total mass of a nucleus to be less than that of the sum of its constituents, and, mainly, because of the appearance of natural isotopes. Thus, Potassium has a mass of 39.10 mainly because of natural K isotopes.
Here is a list of masses of elements and compounds in atomic mass units:
| Compound/element | mass in amu |
| Ar (argon) | 39.948 |
| C | 12.0107 |
| =CH | 13.01864 |
| -CH2- | 14.02658 |
| -CH3 | 15.03452 |
| Xe | 131.293 |
| CO2 (carbon dioxide) | 44.0095 |
| H | 1.00794 |
| H2O (water) | 18.02 |
| N2 (nitrogen) | 28.01 |
Note that sometimes the atomic mass unit is also known as the Dalton (Da), especially when dealing with macromolecules such as proteins.