|Name, Symbol, Number||holmium, Ho, 67|
|Group, Period, Block||n/a, 6, f|
|Appearance||silvery white |
|Atomic mass||164.93032(2) g/mol|
|Electron configuration||[Xe] 4f11 6s2|
|Electrons per shell||2, 8, 18, 29, 8, 2|
|Density (near r.t.)||8.79 g/cm³|
|Liquid density at m.p.||8.34 g/cm³|
|Melting point||1734 K|
(1461 °C, 2662 °F)
|Boiling point||2993 K|
(2720 °C, 4928 °F)
|Heat of fusion||17.0 kJ/mol|
|Heat of vaporization||265 kJ/mol|
|Heat capacity||(25 °C) 27.15 J/(mol·K)|
|Electronegativity||1.23 (Pauling scale)|
|1st: 581.0 kJ/mol|
|2nd: 1140 kJ/mol|
|3rd: 2204 kJ/mol|
|Atomic radius||175 pm|
|Magnetic ordering||no data|
|Electrical resistivity||(r.t.) (poly) 814 nΩ·m|
|Thermal conductivity||(300 K) 16.2 W/(m·K)|
|Thermal expansion||(r.t.) (poly)|
|Speed of sound (thin rod)||(20 °C) 2760 m/s|
|Speed of sound (thin rod)||(r.t.) 64.8 m/s|
|Shear modulus||26.3 GPa|
|Bulk modulus||40.2 GPa|
|Vickers hardness||481 MPa|
|Brinell hardness||746 MPa|
|CAS registry number||7440-60-0|
Holmium (chemical symbol Ho, atomic number 67) is a relatively soft, silvery-white metallic element that is stable in dry air at room temperature. It is a member of the lanthanide series of chemical elements and is also considered one of the "rare earth metals."
Of all the naturally occurring elements, holmium has the highest magnetic moment. It has therefore been used in high-strength magnets to create the strongest artificially generated magnetic fields. In addition, it is suitable for placement in yttrium-iron-garnet (YIG) and yttrium-lanthanum-fluoride (YLF) solid state lasers found in microwave equipment used for medical and dental procedures. Holmium is also useful in nuclear control rods to absorb neutrons produced by nuclear fission reactions and in a certain type of laser to break up kidney stones. Holmium oxide is used as a yellow glass coloring.
Occurrence and isolation
Like the other rare earth elements, holmium is not found as a free element in nature. It occurs combined with other elements in rare-earth minerals, particularly gadolinite and monazite. Its estimated abundance in the Earth's crust is 1.3 milligrams per kilogram.
Holmium is commercially extracted by ion-exchange from monazite sand (0.05 percent holmium), but it remains difficult to separate from other rare earth elements. It has been isolated by the chemical reduction of its anhydrous chloride or fluoride with metallic calcium.
Holmium was discovered by Marc Delafontaine and Jacques-Louis Soret in 1878, when they noticed its unique spectral bands in an absorption spectrum. They called it "Element X." Later that year, Per Teodor Cleve independently discovered the element while working on erbia earth (erbium oxide).
Using a method developed by Carl Gustaf Mosander, Cleve first removed all the known contaminants from erbia and obtained two new materials, one yellowish brown and one green. He named the brown substance holmia (the Latin name for Cleve's hometown, Stockholm), and he called the green one thulia. Holmia was later found to be holmium oxide, and thulia was thulium oxide.
Holmium is an inner transition metal (or lanthanide) that lies in period six of the periodic table, between dysprosium and erbium. This relatively soft, malleable element 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 to form a yellowish oxide. In its pure form, it has a bright silvery luster.
In combining with other elements, holmium exhibits a trivalent character (oxidation number of +3). It has unusual magnetic properties, including the highest magnetic moment (10.6µB) of any naturally occurring element. When combined with yttrium, it forms highly magnetic compounds.
Natural holmium contains one stable isotope, holmium 165. Many synthetic radioactive isotopes are known, of which the most stable one is holmium 163, with a half-life of 4,570 years. All other radioisotopes have half-lives less than 27 hours, and most have half-lives under three hours.
- Holmium(III) oxide (Ho2O3): This yellow solid was first isolated by Cleve from an impure sample of erbia, as mentioned above. Along with dysprosium(III) oxide (Dy2O3), it is among the most powerfully paramagnetic substances known. It is sometimes used in making specialty glasses.
- Given its unique magnetic properties, holmium has been used to create the strongest artificially generated magnetic fields when placed in high-strength magnets as a magnetic pole piece (also called a magnetic flux concentrator).
- Its very high magnetic moment is suitable for use in yttrium-iron-garnet (YIG) and yttrium-lanthanum-fluoride (YLF) solid state lasers found in microwave equipment that is used for medical and dental procedures.
- As it can absorb neutrons from nuclear fission reactions, the element is also used in nuclear control rods.
- Holmium is used in a laser to break up kidney stones while being minimally invasive.
- Holmium oxide is used as a yellow glass coloring.
As with other rare earths, holmium appears to have a low rating for acute toxicity. It plays no biological role in humans but may be able to stimulate metabolism.
- ↑ The term "rare earth metals" (or "rare earth elements") is a trivial name applied to 16 chemical elements: scandium, yttrium, and 14 of the 15 lanthanides (excluding promethium), which occur naturally on Earth. Some definitions also include the actinides. The word "earth" is an obsolete term for oxide. The term "rare earth" is discouraged by the International Union of Pure and Applied Chemistry (IUPAC), as these elements are relatively abundant in the Earth's crust.
ReferencesISBN links support NWE through referral fees
- Chang, Raymond. 2006. Chemistry. 9th ed. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
- Cotton, F. Albert, and Geoffrey Wilkinson. 1980. Advanced Inorganic Chemistry. 4th ed. New York: Wiley. ISBN 0-471-02775-8
- Greenwood, N.N. and A. Earnshaw. 1998. Chemistry of the Elements. 2nd ed. Oxford, U.K.; Burlington, MA: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654 Online version
- "Holmium" Los Alamos National Laboratory, Chemistry Division. Retrieved October 8, 2007.
- Holmium It's Elemental, Jefferson Lab. Retrieved October 8, 2007.
- Jones, Adrian P., Frances Wall, and C. Terry Williams, eds. 1996. Rare Earth Minerals: Chemistry, Origin and Ore Deposits. The Mineralogical Society Series. London, UK: Chapman and Hall. ISBN 0412610302
- Stwertka, Albert. 1998. Guide to the Elements. Rev. ed. Oxford, UK: Oxford University Press. ISBN 0-19-508083-1
All links retrieved January 12, 2018.
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