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Periodic table of the elements, , 1 Alkali metals [ Halogens, group (J Alkaline-earth metals [_] Noble gases, , J Transition metals [_] Rare-earth elements (21, 39, 57-71), [1 Other metals and lanthanoid elements (67-71 only), , [J Other nonmetals, , , , , , = period, +, , _] Actinoid elements, , , , lanthanoid series 6, , actinoid series 7, , *Numbering system adopted by the International Union of Pure and Applied Chemistry (IUPAC). © Encyclopaedia Britannica, Inc.