Saturday, November 13, 2010

Is Yttrium a Rare Earth Element?

Currently being grouped with titanium and zirconium in the first transition metals, does the element yttrium rightfully belong among the rare earth elements?

By: Ringo Bones

Named after the town of Ytterby, Sweden where it was first discovered in 1794; yttrium is a scaly metal with an iron-gray sheen. Primarily used in making phosphors for color TV screens and Microwave filters, yttrium is also well-known in the medical community in the form of yttrium-90, a radioactive isotope that had gained dramatic medical use in needles that had replaced the surgeon’s knife in killing pain-transmitting nerves in the spinal cord. But with an atomic structure and chemical properties resembling more of the rare earths instead of the first transition metals, does this make yttrium a rare earth metal?

From the analytical chemists’ perspective, yttrium, Y, resembles the rare earths more strongly than it does scandium in spite of the fact that it has no 4f-electrons in common with the rare earths. When a rare earth ore is digested with sulfuric acid or fused with potassium bisulfate and the sulfates fractionally crystallized, yttrium is found with the sulfates of dysprosium, holmium, erbium, thulium, ytterbium and lanthanum – the heavy members of the rare earths – in the most soluble fraction. Separation of the Y (III) ion from the other rare earths is achieved most economically and in the highest purity by either ion-exchange or solvent extraction procedures. The hydroxides and oxides of yttrium are somewhat stronger and more soluble than those of terbium but weaker than those of lanthanum. The compound - in general - resembles those of the rare earths of high atomic number – i.e. at the end of the series like ytterbium and lutetium.

For sometime now, the Union of Pure and Applied Chemistry (IUPAC) has placed yttrium in the Group III B of the Periodic Table of the Elements. Chemically, yttrium does possess some very intriguing chemical properties that make it behave as if it is a rare earth element and yet yttrium has no 4f-electrons in common with the rare earths. Given that Dimitri Mendeleyev constructed the Periodic Table of the Elements primarily to arrange individual elements by chemical properties while their atomic structure is of only secondary importance, shouldn’t yttrium belong to the rare earth group of elements instead of in the first transition metals?

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