Chemistry / Unit 2 Chem 0232 short lesson, about 20 seconds
The Atomic Mass Unit
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The idea
The atomic mass unit, or dalton, is defined as exactly one-twelfth the mass of a single carbon-12 atom.
In practice
A proton's mass, about 1.0073 u, and a neutron's, about 1.0087 u, are both measured against this one shared carbon-12 reference.
Where people slip
"Amu" is the older term for the same unit IUPAC now standardizes as the dalton (Da); both names describe one identical definition.
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