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Yttrium is a chemical element with the symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals, and is never found in nature as a free element. ⁸⁹Y is the only stable isotope, and the only isotope found in the Earth's crust.

The most important uses of yttrium are LEDs and phosphors, particularly the red phosphors in television set cathode ray tube displays. Yttrium is also used in the production of electrodes, electrolytes, electronic filters, lasers, superconductors, various medical applications, and tracing various materials to enhance their properties.

Yttrium has no known biological role. Exposure to yttrium compounds can cause lung disease in humans.

The element is named after '' ytterbite'', a mineral first identified in 1787 by the chemist Carl Axel Arrhenius. He named the mineral after the village of Ytterby, in Sweden, where it had been discovered. When one of the chemicals in ytterbite was later found to be the previously unidentified element, yttrium, the element was then named after the mineral.

Characteristics

Properties

Yttrium is a soft, silver-metallic, lustrous and highly crystalline transition metal in group 3. As expected by periodic trends, it is less electronegative than its predecessor in the group, scandium, and less electronegative than the next member of period 5, zirconium; additionally, it is more electronegative than lanthanum, but less electronegative than lutetium due to the lanthanide contraction. Yttrium is the first d-block element in the fifth period.

The pure element is relatively stable in air in bulk form, due to passivation of a protective oxide () film that forms on the surface. This film can reach a thickness of 10  µm when yttrium is heated to 750 ° C in water vapor. When finely divided, however, yttrium is very unstable in air; shavings or turnings of the metal can ignite in air at temperatures exceeding 400 °C. Yttrium nitride (YN) is formed when the metal is heated to 1000 °C in nitrogen.

Similarity to the lanthanides

The similarities of yttrium to the lanthanides are so strong that the element has historically been grouped with them as a rare-earth element, and is always found in nature together with them in rare-earth minerals. Emsley 2001, p. 498 Chemically, yttrium resembles those elements more closely than its neighbor in the periodic table, scandium, Daane 1968, p. 810. and if physical properties were plotted against atomic number, it would have an apparent number of 64.5 to 67.5, placing it between the lanthanides gadolinium and erbium. Daane 1968, p. 815.

It often also falls in the same range for reaction order, resembling terbium and dysprosium in its chemical reactivity. Yttrium is so close in size to the so-called 'yttrium group' of heavy lanthanide ions that in solution, it behaves as if it were one of them. Even though the lanthanides are one row farther down the periodic table than yttrium, the similarity in atomic radius may be attributed to the lanthanide contraction.

One of the few notable differences between the chemistry of yttrium and that of the lanthanides is that yttrium is almost exclusively trivalent, whereas about half the lanthanides can have valences other than three; nevertheless, only for four of the fifteen lanthanides are these other valences important in aqueous solution ( Ce^IV, Sm^II, Eu^II, and Yb^II). Daane 1968, p. 817

Compounds and reactions

As a trivalent transition metal, yttrium forms various inorganic compounds, generally in the oxidation state of +3, by giving up all three of its valence electrons. A good example is yttrium(III) oxide (), also known as yttria, a six-coordinate white solid.

Yttrium forms a water-insoluble fluoride, hydroxide, and oxalate, but its bromide, chloride, iodide, nitrate and sulfate are all soluble in water. The Y³⁺ ion is colorless in solution because of the absence of electrons in the d and f electron shells.

Water readily reacts with yttrium and its compounds to form . Concentrated nitric and hydrofluoric acids do not rapidly attack yttrium, but other strong acids do.

With halogens, yttrium forms trihalides such as yttrium(III) fluoride (), yttrium(III) chloride (), and yttrium(III) bromide () at temperatures above roughly 200 °C. Similarly, carbon, phosphorus, selenium, silicon and sulfur all form binary compounds with yttrium at elevated temperatures.

Organoyttrium chemistry is the study of compounds containing carbon–yttrium bonds. A few of these are known to have yttrium in the oxidation state 0. (The +2 state has been observed in chloride melts, and +1 in oxide clusters in the gas phase.) Some trimerization reactions were generated with organoyttrium compounds as catalysts. These syntheses use as a starting material, obtained from and concentrated hydrochloric acid and ammonium chloride.

Hapticity is a term to describe the coordination of a group of contiguous atoms of a ligand bound to the central atom; it is indicated by the Greek character ''eta'', η. Yttrium complexes were the first examples of complexes where carboranyl ligands were bound to a d⁰-metal center through a η⁷-hapticity. Vaporization of the graphite intercalation compounds graphite–Y or graphite– leads to the formation of endohedral fullerenes such as Y@C₈₂. Electron spin resonance studies indicated the formation of Y³⁺ and (C₈₂)³⁻ ion pairs. The carbides Y₃C, Y₂C, and YC₂ can be hydrolyzed to form hydrocarbons.

Isotopes and nucleosynthesis

Yttrium in the Solar System was created through stellar nucleosynthesis, mostly by the s-process (≈72%), but also by the r-process (≈28%). The r-process consists of rapid neutron capture by lighter elements during supernova explosions. The s-process is a slow neutron capture of lighter elements inside pulsating red giant stars.

Yttrium isotopes are among the most common products of the nuclear fission of uranium in nuclear explosions and nuclear reactors. In the context of nuclear waste management, the most important isotopes of yttrium are ⁹¹Y and ⁹⁰Y, with half-lives of 58.51 days and 64 hours, respectively. Though ⁹⁰Y has a short half-life, it exists in secular equilibrium with its long-lived parent isotope, strontium-90 (⁹⁰Sr) with a half-life of 29 years.

All group 3 elements have an odd atomic number, and therefore few stable isotopes. Scandium has one stable isotope, and yttrium itself has only one stable isotope, ⁸⁹Y, which is also the only isotope that occurs naturally. However, the lanthanide rare earths contain elements of even atomic number and many stable isotopes. Yttrium-89 is thought to be more abundant than it otherwise would be, due in part to the s-process, which allows enough time for isotopes created by other processes to decay by electron emission (neutron → proton). Such a slow process tends to favor isotopes with atomic mass numbers (A = protons + neutrons) around 90, 138 and 208, which have unusually stable atomic nuclei with 50, 82, and 126 neutrons, respectively. This stability is thought to result from their very low neutron-capture cross-section. . Electron emission of isotopes with those mass numbers is simply less prevalent due to this stability, resulting in them having a higher abundance. ⁸⁹Y has a mass number close to 90 and has 50 neutrons in its nucleus.

At least 32 synthetic isotopes of yttrium have been observed, and these range in atomic mass number from 76 to 108. The least stable of these is ¹⁰⁶Y with a half-life of >150  ns (⁷⁶Y has a half-life of >200 ns) and the most stable is ⁸⁸Y with a half-life of 106.626 days. Apart from the isotopes ⁹¹Y, ⁸⁷Y, and ⁹⁰Y, with half-lives of 58.51 days, 79.8 hours, and 64 hours, respectively, all the other isotopes have half-lives of less than a day and most of less than an hour.

Yttrium isotopes with mass numbers at or below 88 decay primarily by positron emission (proton → neutron) to form strontium ( Z = 38) isotopes. Yttrium isotopes with mass numbers at or above 90 decay primarily by electron emission (neutron → proton) to form zirconium (Z = 40) isotopes. Isotopes with mass numbers at or above 97 are also known to have minor decay paths of β⁻ delayed neutron emission.

Yttrium has at least 20 metastable ("excited") isomers ranging in mass number from 78 to 102. Multiple excitation states have been observed for ⁸⁰Y and ⁹⁷Y. While most of yttrium's isomers are expected to be less stable than their ground state, ^78mY, ^84mY, ^85mY, ^96mY, ^98m1Y, ^100mY, and ^102mY have longer half-lives than their ground states, as these isomers decay by beta decay rather than isomeric transition.

History

In 1787, part-time chemist Carl Axel Arrhenius found a heavy black rock in an old quarry near the Swedish village of Ytterby (now part of the Stockholm Archipelago). Thinking it was an unknown mineral containing the newly discovered element tungsten, Emsley 2001, p. 496 he named it ''ytterbite'' and sent samples to various chemists for analysis. Van der Krogt 2005

Johan Gadolin at the University of Åbo identified a new oxide (or "earth") in Arrhenius' sample in 1789, and published his completed analysis in 1794. Anders Gustaf Ekeberg confirmed the identification in 1797 and named the new oxide ''yttria''. In the decades after Antoine Lavoisier

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