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GCSE Chemistry · key term
A historical measure of an element’s atomic mass relative to that of another atom; it corresponds broadly to what is now called relative atomic mass.
Used by AQA
Specification 4.1.2.2 · Paper 1
Revise: History of the Periodic TableInstead, they tried placing elements in order of increasing atomic weight. This was a sensible starting point because atomic weights could be estimated experimentally and some chemical properties seemed to recur as the weights increased.
For a question asking how the periodic table developed, give the stages in chronological order: ordering by atomic weight, problems with early tables, Mendeleev’s gaps and changes, successful predictions, then the explanation provided by isotopes and atomic number.
Do not say that Mendeleev simply ignored atomic weights. He generally used increasing atomic weight, but changed the order where necessary to keep elements with similar properties together.
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