BRAINCAKERelative Atomic Mass
The relative atomic mass is the weighted mean mass of an atom of an element compared to 1/12th the mass of a carbon-12 atom which has a mass of 12.
The symbol for relative atomic mass is Ar. Like relative isotopic mass it is a ratio, so it has no units.
Most elements exist as a mixture of isotopes, and each isotope makes up a fixed percentage of the element, called its abundance. The relative atomic mass takes both the mass and the abundance of each isotope into account, which is why it is a weighted mean.
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Key terms in this lesson
- relative isotopic mass
- The mass of one atom of an isotope compared with 1/12 of the mass of one atom of carbon-12.
More in Atomic Structure
- Structure of the Atom
- Atomic Number and Mass Number
- Isotopes
- Relative Isotopic Mass
- Mass Spectrometer
- Relative Atomic Mass from a Mass Spectrometer
- Relative Molecular Mass from a Mass Spectrometer
- Quantum Shells
All 19 lessons in Atomic Structure · All Edexcel AS-level Chemistry topics