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The actinide series encompasses the 15 chemical elements that lie between actinium and lawrencium on the periodic table with atomic numbers 89 - 103. The actinide series is named after actinium. All actinides are f-block elements except lawrencium. There are also alternative arrangements which do not include either actinum or lawrencium in the actinide series. Actinides have chemically similar characteristics to the elements of the lanthanide series, and to scandium and yttrium, but actinides are all radioactive. The actinides with higher atomic numbers are not found in nature and have short half-lives.
The actinides are typically placed below the main body of the periodic table, in the manner of a footnote. The full-width version of the periodic table shows the position of the actinides more clearly.
Note that the International Union of Pure and Applied Chemistry (IUPAC) are currently recommending the name actinoid rather than actinide, as the suffix "-ide" is generally used to indicate anions.
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