Holmium is a chemical element with the symbol Ho and atomic number 67. Part of the lanthanide series, holmium is a rare earth element. Holmium was discovered by Swedish chemist Per Theodor Cleve. Its oxide was first isolated from rare earth ores in 1878 and the element was named after the city of Stockholm. Elemental holmium is a relatively soft and malleable silvery-white metal. It is too reactive to be found uncombined in nature, but when isolated, is relatively stable in dry air at room temperature. However, it reacts with water and rusts readily, and will also burn in air when heated. Holmium is found in the minerals monazite and gadolinite, and is usually commercially extracted from monazite using ion exchange techniques. Its compounds in nature, and in nearly all of its laboratory chemistry, are trivalently oxidized, containing Ho(III) ions. Trivalent holmium ions have fluorescent properties similar to many other rare earth ions (while yielding their own set of unique emission light lines), and holmium ions are thus used in the same way as some other rare earths in certain laser and glass colorant applications. Holmium has the highest magnetic strength of any element and therefore is used for the polepieces of the strongest static magnets. Because holmium strongly absorbs neutrons, it is also used as a burnable poison in nuclear reactors. Holmium is a relatively soft and malleable element that is fairly corrosion-resistant and stable in dry air at standard temperature and pressure. In moist air and at higher temperatures, however, it quickly oxidizes, forming a yellowish oxide. In pure form, holmium possesses a metallic, bright silvery luster. Holmium oxide has some fairly dramatic color changes depending on the lighting conditions. In daylight, it is a tannish yellow color. Under trichromatic light, it is a fiery orange red, almost indistinguishable from the appearance of erbium oxide under the same lighting conditions. The change is related to the sharp emission bands of the trivalent ions of these elements, acting as phosphors. Holmium has the highest magnetic moment (10.6 µB) of any naturally occurring element and possesses other unusual magnetic properties. When combined with yttrium, it forms highly magnetic compounds.Holmium is paramagnetic at ambient conditions, but is ferromagnetic at temperatures below 19 K. Chemical properties Holmium metal tarnishes slowly in air and burns readily to form holmium(III) oxide: 4 Ho + 3 O2 → 2 Ho2O3 Holmium is quite electropositive and is generally trivalent. It reacts slowly with cold water and quite quickly with hot water to form holmium hydroxide: 2 Ho (s) + 6 H2O (l) → 2 Ho(OH)3 (aq) + 3 H2 (g) Holmium metal reacts with all the halogens: 2 Ho (s) + 3 F2 (g) → 2 HoF3 (s) [pink] 2 Ho (s) + 3 Cl2 (g) → 2 HoCl3 (s) [yellow] 2 Ho (s) + 3 Br2 (g) → 2 HoBr3 (s) [yellow] 2 Ho (s) + 3 I2 (g) → 2 HoI3 (s) [yellow] Holmium dissolves readily in dilute sulfuric acid to form solutions containing the yellow Ho(III) ions, which exist as a [Ho(OH2)9]3+ complexes: 2 Ho (s) + 3 H2SO4 (aq) → 2 Ho3+ (aq) + 3 SO2− 4 (aq) + 3 H2 (g) Holmiums most common oxidation state is +3. Holmium in solution is in the form of Ho3+ surrounded by nine molecules of water. Holmium dissolves in acids.
Posted on: Thu, 26 Jun 2014 00:10:04 +0000
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