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Any of the series of 15 consecutive chemical elements in the periodic table from lanthanum to lutetium (atomic numbers 57–71). With scandium and yttrium, they make up the rare earth metals. Their atoms have similar configurations and similar physical and chemical behaviour; the most common valences are 3 and 4.
This entry comes from Encyclopædia Britannica Concise. For the full entry on lanthanide, visit Britannica.com.