BACK TO atomic weight

atomic weight vs. mass number

  1. the average weight of an atom of an element, formerly based on the weight of one hydrogen atom taken as a unit or on 1/16 (0.0625) the weight of an oxygen atom, but after 1961 based on 1/12 the weight of the carbon-12 atom. Abbreviation: at. wt.
  1. the integer nearest in value to the atomic weight of an atom and equal to the number of nucleons in the nucleus of the atom. Symbol: A

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