|Name, Symbol, Number||holmium, Ho, 67|
|Group, Period, Block||n/a, 6, f|
|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.
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.
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