[2] Preparation, Phase Equilibria, Crystal Chemistry and Some Properties of Lanthanide Hydroxide Nitrates,J.M.Haschke, Inorg.Chem., 1974, 13(8), 181213
NOMENCLATUREThe International Union of Pure and Applied Chemistry (IUPAC) is accepted world-wide asthe arbiter in chemical nomenclature and produces rules for naming chemical compounds. Therules for inorganic compounds[1] discuss the terminology recommended for element 39, Yttrium,and elements 57 to 71, Lanthanum to Lutetium.The relevant paragraph, 1.3.8.2 .. Collective Names of Groups of Atoms, states:• the following collective names for groups of atoms are IUPAC approved :• lanthanoids or lanthanides (La, Ce . ..........Yb, Lu) (Note 3h)• rare earth metals (Sc, Y, and the lanthanoids)The "note 3h" adds a comment, using "actinium" to illustrate the example but explicitly defining"lanthanum" to be handled in a similar manner.Although [lanthanoid] means "like [lanthanum]" and so should not include [lanthanum],[lanthanum] has been included by common usage. The ending -ide normally indicates a negativeion, and therefore "lanthanoid" [is] preferred to "lanthanide". However, owing to wide currentuse, lanthanide [is] still allowed.(The 1960 IUPAC rules differentiated between lanthanide and the term "lanthanon". Lanthan-idemeant elements 58 to 71 whereas lanthan- on meant lanthan-ides plus lanthan-um, i.e. elements 57to 71. This subtle distinction is now rarely used).There is of course a body of usage dating back even further than the rules. The full collective term,and pedantically correct, "rare earth metals", is often replaced by the shortened term "rare earths".This is frequently taken to mean - erroneously -just the fifteen elements 57 to 71; that is scandiumand yttrium are not considered "rare earths". This is implicit in, for example, article titles andabstract entries that read:• Rare Earth Elements and Yttrium• Rare Earths (Lanthanides)• Lanthanides, see Rare Earths ...There is now wide acceptance - acknowledged in the latest IUPAC rules - that, when anycollective term is used, the label refers to elements 57 - 71 and not just to[1] Nomenclature of Inorganic Chemistry, Recommendations 1990, International Union of Pure and AppliedChemistry, ed. G.J.Leigh, p. 43, publ. Blackwell 199014