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GCSE Chemistry · key term
The weighted mean mass of the atoms of an element compared with one-twelfth of the mass of a carbon-12 atom.
Used by AQA, Edexcel and OCR
Specification 4.1.1.6, 4.1.2.2, 4.1.2.4, 4.3.1.2 · Paper 1
The abundance-weighted mean mass of the atoms of an element compared with one-twelfth of the mass of a carbon-12 atom. It has no unit and is written .
Revise: Relative Atomic MassRelative atomic mass is the weighted mean mass of the atoms of an element compared with one-twelfth of the mass of a carbon-12 atom. It has no unit because it is a comparison of masses.
Do not confuse relative atomic mass, , with mass number. is an abundance-weighted average for an element; mass number describes one particular atom.
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The weighted mean mass of the atoms of an element, taking account of the relative abundances of its isotopes.
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of a carbon-12 atom.
The mean mass of the atoms of an element compared with one-twelfth of the mass of a carbon-12 atom; its symbol is .
Specification 1.11, 1.12, 1.13, 1.44 · Paper 1, Paper 2
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of a carbon-12 atom.
Revise: Relative Atomic MassesRelative atomic mass takes a weighted mean of their masses.
The mass of an atom relative to one-twelfth of the mass of a carbon-12 atom; it is written as .
The average mass of an atom of an element compared with one-twelfth of the mass of a carbon-12 atom.
Specification C2.2i · Paper 1 (Foundation), Paper 3 (Higher)
The weighted mean mass of an atom of an element compared with one-twelfth of the mass of a carbon-12 atom.
Revise: Development of the Periodic TableDuring the nineteenth century, scientists did not yet understand protons or atomic number, so they used the measurable information available to them, especially relative atomic masses and chemical properties.
Paper 1 (Foundation), Paper 2 (Foundation), Paper 3 (Higher), Paper 4 (Higher)
The weighted mean mass of the atoms of an element, taking account of its different isotopes, relative to one-twelfth of the mass of a carbon-12 atom.
Revise: Calculating particle numbersDo not confuse mass number with relative atomic mass. The relative atomic mass printed in a Periodic Table is a weighted mean for the element’s naturally occurring isotopes, so it is often not a whole number. For example, a decimal relative atomic mass describes an average rather than the nucleus of one atom.
The average mass of an element's atoms compared with one-twelfth of the mass of a carbon-12 atom; it is not the mass number of one particular atom.
The mass of an atom compared with a standard reference mass; its value, Aᵣ, has no unit.
Relative atomic mass has no unit. Follow any rounding instruction in the question.
Do not confuse mass number with relative atomic mass. Mass number belongs to one isotope and is a whole number; relative atomic mass is a weighted mean for all the naturally occurring isotopes of an element.