atomic mass unit
4 synonyms for atomic mass unit, grouped by meaning and by how common each one is.
Noun — A standard unit for stating the masses of atoms and molecules, defined as exactly one twelfth of the mass of a single carbon-12 atom, which is about 1.66 x 10^-27 kilograms. It is symbolised u or amu and is also called the dalton.
Synonyms
Less common
Still standard English, but they carry more weight.
Rare, literary or technical
Precise, but they will stand out — check the sense before using one.
unified atomic mass unit
amu
u
How to use atomic mass unit
The word patterns that sound natural to a native speaker.
expressed in atomic mass units
one atomic mass unit
unified atomic mass unit
atomic mass unit to kg
Technical. Chemists and physicists increasingly prefer dalton (Da), especially in biochemistry.
Etymology
A descriptive compound: atomic, from Greek atomos 'indivisible', plus mass unit.
Full origin of atomic mass unit →Frequently asked questions
What is the difference between atomic mass unit and atomic mass?
The atomic mass unit is the unit of measurement; atomic mass is the quantity being measured. So an atom of oxygen-16 has an atomic mass of about 16, expressed in atomic mass units.
Is a dalton the same as an atomic mass unit?
Yes. The dalton (Da) and the unified atomic mass unit (u) are identical in value. Dalton is the name preferred by the international standards bodies and is standard in biochemistry, where protein masses are given in kilodaltons.
Why is carbon-12 used as the reference?
Carbon-12 is a stable, abundant isotope that can be measured very precisely in a mass spectrometer. Fixing its mass at exactly 12 gives a reference that produces whole-number-ish masses for most isotopes and avoids the inconsistencies of the older oxygen-based scales.
