Professional paper

https://doi.org/10.15255/KUI.2018.042

What is Relative Atomic Mass?

Nenad Raos ; Institute for Medical Research and Occupational Health, Ksaverska c. 2, 10 000 Zagreb, Croatia

Abstract

There are two basic understandings of relative atomic mass. The first (“atomic weight”) stems from the law of constant and multiple mass proportions and has no reference to the size and the absolute mass of atoms. “Atomic weights” were defined and measured in the 19th Century, and at that time atoms and molecules were just hypothetical particles. However, in the 20th Century, it became possible to measure the number and mass of atoms, and relative atomic mass was defined in reference to the mass and number of atoms, i.e. Avogadro constant and mole. This also resulted in the change of reference unit, A_r(H) = 1 or A_r(O) = 16, for A_r(12C) = 12, and the way of teaching of stoichiometry (calculations via n_A instead of using proportionality principle). This article also describes the history of “atomic weight” determination by gravimetric analysis, especially the work of J. J. Berzelius and J. S. Stas.




This work is licensed under a Creative Commons Attribution 4.0 International License.

Keywords

chemistry education; history of chemistry; Dalton; Berzelius; Richter; Stas

Hrčak ID:

257559

URI

https://hrcak.srce.hr/257559

Publication date:

18.5.2021.

Article data in other languages: croatian

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