Historia de pesos atomicos

INTERNATIONAL UNION OF PURE AND APPLIED CHEMISTRY
INORGANIC CHEMISTRY DIVISION COMMISSION ON ATOMIC WEIGHTS AND * ISOTOPIC ABUNDANCES

HISTORY OF THE RECOMMENDED ATOMIC-WEIGHT VALUES FROM 1882 TO 1997: A COMPARISON OF DIFFERENCES FROM CURRENT VALUES TO THE ESTIMATED UNCERTAINTIES OF EARLIER VALUES
(Technical Report)

Prepared for publication by T. B.COPLEN and H. S. PEISER U.S. GeologicalSurvey, 431 National Center, Reston, Virginia 20192, USA

*

Membership of the Commission for the period 1996–1997 was as follows:

L. Schultz (FRG, Chairman); R. D. Vocke (USA, Secretary); J.K. Böhlke (USA, Associate); H.-J. Dietze (FRG, Associate); T. Ding (China, Associate); M. Ebihara (Japan, Titular); J. W. Gramlich (USA, Associate); A. N. Halliday (USA, Associate); H.-J. Kluge (FRG,Associate); H. R. Krouse (Canada, Titular); R. D. Loss (Australia, Titular); G. I. Ramendik (Russia, Titular); D. E. Richardson (USA, Associate); M. Stiévenard (France, Associate); P. D. P. Taylor (Belgium, Titular); J. R. de Laeter (Australia, National Representative); P. De Bièvre (Belgium, National Representative); Y. Xiao (China, National Representative); M. Shima (Japan, NationalRepresentative); N. N. Greenwood (UK, National Representative); H. S. Peiser (USA, National Representative).

History of the Recommended Atomic-Weight Values from 1882 to 1997: A Comparison of Differences from Current Values to the Estimated Uncertainties of Earlier Values (Technical Report)
Abstract—International commissions and national committees for atomic weights (mean relative atomic masses) haverecommended regularly updated, best values for these atomic weights as applicable to terrestrial sources of the chemical elements. Presented here is a historically complete listing starting with the values in F. W. Clarke's 1882 recalculation, followed by the recommended values in the annual reports of the American Chemical Society's Atomic Weights Commission. From 1903, an International Commissionpublished such reports and its values (scaled to an atomic weight of 16 for oxygen) are here used in preference to those of national committees of Britain, Germany, Spain, Switzerland, and the U.S.A. We have, however, made scaling adjustments from Ar(16O) to Ar(12C) where not negligible. From 1920, this International Commission constituted itself under the International Union of Pure and AppliedChemistry (IUPAC). Since then, IUPAC has published reports (mostly biennially) listing the recommended atomic weights, which are reproduced here. Since 1979, these values have been called the “standard atomic weights” and, since 1969, all values have been published with their estimated uncertainties. Few of the earlier values were published with uncertainties. Nevertheless, we assessed suchuncertainties on the basis of our understanding of the likely contemporary judgement of the values' reliability. While neglecting remaining uncertainties of 1997 values, we derive “differences” and a retrospective index of reliability of atomic-weight values in relation to assessments of uncertainties at the time of their publication. A striking improvement in reliability appears to have been achieved sincethe commissions have imposed upon themselves the rule of recording estimated uncertainties from all recognized sources of error.

COMMENT At frequent intervals (biennially in recent times), the International Union of Pure and Applied Chemistry (IUPAC) publishes revised tables of recommended atomic-weight values, Ar(E), for chemical element E. Recent editions of tables include uncertainties,U[Ar(E)], and refer to the tabulated Ar(E) values as “standard atomic weights” applicable reliably to normal terrestrial sources. The latest such IUPAC table is based on a 1 reevaluation in 1997 (ref. ). In the table submitted here (Table 1), we list all recommended values since 1882, but exclude radioactive elements without stable isotopes (or radio-isotopes with half-lives comparable to the age...