amu
Units & Measurements abbreviation · Metric and SI Unit
| Stands for | Atomic mass unit |
|---|---|
| Categories | Units & Measurements |
amu stands for Atomic mass unit, a metric and SI unit abbreviation.
A unit of mass for atoms and molecules equal to one twelfth of the mass of a carbon-12 atom, about 1.6605 × 10^-27 kg. Periodic tables list atomic masses on this scale, about 1.008 for hydrogen and 12.011 for carbon.
Example: A water molecule has a mass of about 18 amu.
Usage notes
The modern accepted symbol is u, the unified atomic mass unit, and the dalton (Da) is another name for the same quantity; amu remains common in high-school and introductory chemistry. Before 1961, physicists based the amu on oxygen-16 and chemists on natural oxygen, giving slightly different values until the carbon-12 standard unified them.