Notes on the Periodic Table
The atomic weights and names on this periodic table are derivied from the most recent accepted values (1997) from the International Union of Pure and Applied Chemistry (IUPAC) and its Commission on Atomic Weights and Isotopic Abundances. The 1997 values are the commissions's current best knowledge of the atomic weights and represent the closest available approach to the hypothetical "error-free" values.
For easier reference, the last digit of uncertainty has been removed. Thus, all written digits are significant. To find the last digits, go to the IUPAC Atomic Weights Reference Page.
All radioactive elements have the atomic weight of their most-stable (longest-lived) isotope. Thorium, protactinium, and uranium are also radioactive but occur naturally on Earth in certain characteristic isotopes. These isotopes have been tabulated accordingly.
Characteristics of the Periods and Groups
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