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出典:『Wikipedia』 (2011/06/12 21:11 UTC 版)

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The group 3 elements are a group of chemical elements in the periodic table. This group, like other d-block ones, should contain four elements, but it is not agreed what elements is the group composed of. Scandium (Sc) and yttrium (Y) are always included, but the later two spaces are usually occupied by lanthanum (La) and actinium (Ac), or by lutetium (Lu) and lawrencium (Lr); less frequently, it is considered the group should be expanded to 30 elements (with all the lanthanides and actinides included) or contracted to contain only scandium and yttrium. The group itself has not acquired a trivial name; however, scandium, yttrium and the lanthanides are sometimes called rare earth metals.