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Vol. 35 No. 4
July-August 2013

Making an imPACt | Recent IUPAC technical reports and recommendations that affect the many fields of pure and applied chemistry.
See also www.iupac.org/publications/pac

Atomic Weights of the Elements 2011 (IUPAC Technical Report)

Michael E. Wieser, et al.
Pure and Applied Chemistry, 2013
Vol. 85, No. 5, pp. 1047–1078

The latest tables of atomic weights (2011) are published in Pure and Applied Chemistry.1 This biennial review of atomic-weight determinations and other cognate data has resulted in changes for the standard atomic weights of five elements: the atomic weight of bromine has changed from 79.904(1) to the interval [79.901, 79.907], germanium from 72.63(1) to 72.630(8), indium from 114.818(3) to 114.818(1), magnesium from 24.3050(6) to the interval [24.304, 24.307], and mercury from 200.59(2) to 200.592(3).

For bromine and magnesium, assignment of intervals for the new standard atomic weights reflects the common occurrence of variations in the atomic weights of those elements in normal terrestrial materials.2 As such, bromine and magnesium have joined the earlier group of 10 elements—hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, and thallium—which were expressed as intervals for the first time in the 2009 review to more accurately convey atomic weight variation.

The proper expression for an interval according to the latest International Vocabulary of Metrology is [a, b]. In this report therefore the notation of these atomic weights intervals has changed from [a; b], as they were first reporterd, to [a, b].

  1. PAC 2013. For a collection of the reviews of the atomic weights of the elements, see www.iupac.org/publications/pac/series/atomicweights/
  2. T.B. Coplen and N.E. Holden, “Atomic Weights—No Longer Constants of Nature” Mar-Apr 2011 CI, pp. 10–15; www.iupac.org/publications/ci/2011/3302/2_coplen.html

http://dx.doi.org/10.1351/PAC-REP-13-03-02

 


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