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Carbon-12

Carbon-12 is used as the standard isotope on which to base all the masses of atoms. A Carbon-12 atom is given a mass of 12u (atomic units) and the mass of all other atoms are compared to it and measured in atomic units.

One atomic unit (1u) is equal to 1/12 th the mass of a carbon-12 atom.

One atomic unit is equal to the mean mass of a neutron and proton.

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Specification: OCR Chemistry A (H032), AS-level, 2.1.1 Atomic structure and isotopes. Topic: Atoms, Ions and Compounds.

Key terms in this lesson

Isotopes
Atoms of the same element with the same number of protons but different numbers of neutrons.
Base
A proton acceptor.

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