atomic mass unit
Definition
Noun: - A unit of mass used to express the masses of atoms, molecules, and nuclear particles. It is defined as one twelfth of the mass of an atom of carbon-12 in its ground state.
Usage
The atomic mass unit (amu or u) is the standard unit in chemistry and physics for describing atomic-scale masses. It allows for convenient comparison between the masses of different atoms and subatomic particles. - It is used when stating the atomic weight or relative atomic mass of an element. - It is used to express the mass of molecules (molecular mass) and isotopes.
Examples
- The atomic mass of a proton is approximately 1.0073 atomic mass units.
- An oxygen-16 atom has a mass of about 16 atomic mass units.
- The molecular mass of water (H₂O) is roughly 18.015 atomic mass units.
Advanced Usage
- Unified atomic mass unit (u or Da): The modern, standardized term, where 'Da' stands for dalton. It is synonymous with the atomic mass unit.
- The protein's mass was measured as 64,000 daltons (64 kDa).
- The atomic mass unit allows scientists to use a scale where the mass of a carbon-12 atom is exactly 12 u, simplifying calculations.
Variants and Related Words
- Dalton (Da): A unit of mass equal to the unified atomic mass unit. Commonly used in biochemistry and molecular biology.
- Relative atomic mass: A dimensionless number representing the ratio of the average mass per atom of an element to 1/12 of the mass of a carbon-12 atom. It is numerically close to the atomic mass in amu.
Synonyms
- Unified atomic mass unit (u)
- Dalton (Da)
Related Phrases/Concepts
- Atomic weight: The average mass of atoms of an element, measured in atomic mass units, weighted by isotopic abundance.
- Molar mass: The mass of one mole of a substance, expressed in grams per mole (g/mol). Numerically, it is equal to the atomic or molecular mass in atomic mass units.
Noun
-
unit of mass for expressing masses of atoms or molecules
