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Unformatted text preview: STANDARD ATOMIC WEIGHTS (2005) This table of atomic weights includes the changes made in 2005 by the IUPAC Commission on Isotopic Abundances and Atomic Weights . Those changes affected the following elements: Al, Au, Bi, Co, Cs, La, Mn, Na, Nd, P, Pt, Sm, Sc, Ta, Tb, and Th . The Standard Atomic Weights apply to the elements as they ex- ist naturally on Earth, and the uncertainties take into account the isotopic variation found in most laboratory samples . Further com- ments on the variability are given in the footnotes . The number in parentheses following the atomic weight value gives the uncertainty in the last digit . An atomic weight entry in brackets indicates that the element that has no stable isotopes; the value given is the atomic mass in u (or the mass number, if the mass is not accurately known) for the isotope of longest half-life . Thorium, protactinium, and uranium have no stable isotopes, but the terrestrial isotopic composition is sufficiently uniform to per- mit a standard atomic weight to be specified . References 1 . Chemistry International , Vol . 27, No . 6, p .18, 2005 . 2 . Coplen, T . D ., Pure Appl. Chem 73, 667, 2001 . 3 . Coplen, T . D ., J. Phys. Chem. Ref. Data , 30, 701, 2001 ....
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