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Relative Atomic Mass

Because most elements have more than one isotope and naturally occurring elements have different proportions of each isotope, the relative atomic mass is used for calculations involving the mass of atoms.:

The relative atomic mass is the weighted mean mass of all the isotopes of the atoms of an element compared to one-twelfth the mass of a carbon-12 atom.

The relative atomic mass is calculated by adding the products of the mass of the isotopes and their relative frequencies.

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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.

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