BRAINCAKERelative Isotopic Mass
The relative isotopic mass is the mass of an atom of an isotope compared to 1/12th the mass of a C-12 atom.
More precisely, the relative isotopic mass is the mass of an atom of an isotope relative to 1/12 of the mass of an atom of carbon-12.
Carbon-12 is the standard. By definition an atom of carbon-12 has a relative isotopic mass of exactly 12, so 1/12 of its mass is 1 unit, roughly the mass of one proton or one neutron.
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Key terms in this lesson
- mass number
- The total number of protons and neutrons in the nucleus of an atom.
More in Atomic Structure
- Discovery of Atomic Structure
- Structure of the Atom
- Atomic Number and Mass Number
- Isotopes
- Relative Atomic Mass
- Mass Spectrometer
- Relative Atomic Mass from a Mass Spectrometer
- Relative Molecular Mass from a Mass Spectrometer
All 19 lessons in Atomic Structure · All Edexcel AS-level Chemistry topics