
Atomic Weights of 10 Elements on Periodic Table to Change - J3L2404
http://www.scientificcomputing.com/news-DS-Atomic-Weights-of-10-Elements-on-Periodic-Table-to-Change-122110.aspx
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gus_massa
The article has error or at least it is misleading.

Short version:

* ~1815-~1960 they use the H=1 or O=16 scales. They are two different scales, some people preferred one and other people preferred the otter one. In one of them H has "weight" 1 and in the other O has "weight" 16.

* From ~1960 they use the C_12=12 scale. This is another scale, where the isotope 12 of carbon has "weight" 12.

* There are a lot of technical modifications and, corrections during these 200 ~years. This a simplification of the history.

Also, from 1951 the atomic weights of some elements have uncertainties.

    
    
      Based on a report by Marble 98 , a range was finally 
      added to the atomic weight value of sulfur for the first 
      time in the 1951 report 99 . In the 1961 report 65 , 
      ranges were listed for six elements due to the natural 
      variation in their isotopic composition and experimental 
      uncertainties were added for five other elements 
      following a systematic review by Cameron and Wichers.
    

So in the last 100 years there has been a lot of changes, a los of
codifications and a atomic weight had uncertainties. Apparently this will only
be a new way to show the uncertainties.

Looong version: <http://www.iupac.org/publications/ci/2004/2601/1_holden.html>

