Antimony
Antimony is a chemical element with the symbol Sb and atomic number 51. A lustrous grey metal or metalloid, it occurs in nature mainly in the form of the sulfide mineral stibnite. Antimony compounds have been known since ancient times and were powdered for use as medicine and cosmetics, often known by the Arabic name kohl.
China is the largest producer of antimony and its compounds, with most production coming from the Xikuangshan Mine in Hunan. The industrial methods for refining antimony from stibnite are roasting followed by reduction with carbon, or direct reduction of stibnite with iron.
The most common applications for metallic antimony are in alloys with lead and tin, which have improved properties for solders, bullets, and plain bearings. It improves the rigidity of lead-alloy plates in lead–acid batteries. Antimony trioxide is a prominent additive for halogen-containing flame retardants. Antimony is used as a dopant in semiconductor devices.
Characteristics
Properties
Antimony is a member of group 15 of the periodic table. As one of the elements called pnictogens, it has an electronegativity of 2.05. In accordance with periodic trends, it is more electronegative than tin or bismuth, and less electronegative than tellurium or arsenic. As a metalloid, it has a Mohs scale hardness of 3.Antimony is a silvery, lustrous gray solid that is stable in air at room temperature. If heated, it reacts with oxygen to produce antimony trioxide,. Antimony is attacked by oxidizing acids.
The stable allotrope of antimony crystallises in a trigonal cell, isomorphic with bismuth and the gray allotrope of arsenic.
A yellow allotrope of antimony, assumed to be analogous to yellow arsenic, forms by oxidation of stibine with air or oxygen at −90 °C. At ambient temperatures and in ambient light, it transforms into the more stable black allotrope. A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride, but it always contains appreciable chlorine and is not really an antimony allotrope. When scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms; when rubbed with a pestle in a mortar, a strong detonation occurs.
Elemental antimony adopts a layered structure whose layers consist of fused, ruffled, six-membered rings. The nearest and next-nearest neighbors form an irregular octahedral complex, with the three atoms in each double layer slightly closer than the three atoms in the next. This relatively close packing leads to a high density of 6.697 g/cm3, but the weak bonding between the layers leads to the low hardness and brittleness of antimony.
Isotopes
Antimony has two stable isotopes: with a natural abundance of 57.21% and with a natural abundance of 42.79%. There are 37 artificial radioactive isotopes known with mass numbers 104 to 142, of which the longest-lived is the fission product with a half-life of 2.758 years. Numerous meta states are known, of which the most stable is with a half-life of 5.76 days. Isotopes that are lighter than the stable tend to undergo β+ decay, and those that are heavier β− decay, with some exceptions.Occurrence
The abundance of antimony in the Earth's crust is estimated at 0.2 parts per million, comparable to thallium at 0.5 ppm and silver at 0.07 ppm. It is the 63rd most abundant element in the crust. Even though this element is not abundant, it is found in more than 100 mineral species. Antimony is sometimes found natively, but more frequently it is found in the sulfide stibnite which is the predominant ore mineral.Compounds
Antimony compounds are often classified according to their oxidation state: Sb and Sb. The +5 oxidation state is more common.Oxides and hydroxides
is formed when antimony is burnt in air. In the gas phase, the molecule of the compound is, but it polymerizes upon condensing. Antimony pentoxide can be formed only by oxidation with concentrated nitric acid. Antimony also forms a mixed-valence oxide, antimony tetroxide, which features both Sb and Sb. Unlike oxides of phosphorus and arsenic, these oxides are amphoteric, do not form well-defined oxoacids, and react with acids to form antimony salts.Antimonous acid is unknown, but the conjugate base sodium antimonite forms upon fusing sodium oxide and. Transition metal antimonites are also known. Antimonic acid exists only as the hydrate, forming salts as the antimonate anion. When a solution containing this anion is dehydrated, the precipitate contains mixed oxides.
The most important antimony ore is stibnite. Other sulfide minerals include pyrargyrite, zinkenite, jamesonite, and boulangerite. Antimony pentasulfide is non-stoichiometric, which features antimony in the +3 oxidation state and S–S bonds. Several thioantimonides are known, such as and.
Halides
Antimony forms two series of halides: and. The trihalides,,, and are all molecular compounds having trigonal pyramidal molecular geometry. The trifluoride is prepared by the reaction of antimony trioxide with hydrofluoric acid:It is Lewis acidic and readily accepts fluoride ions to form the complex anions and. Molten antimony trifluoride is a weak electrical conductor. The trichloride is prepared by dissolving stibnite in hydrochloric acid:
Arsenic sulfides are not readily attacked by the hydrochloric acid, so this method offers a route to As-free Sb.
The pentahalides and have trigonal bipyramidal molecular geometry in the gas phase, but in the liquid phase, is polymeric, whereas is monomeric. Antimony pentafluoride is a powerful Lewis acid used to make the superacid fluoroantimonic acid.
Oxyhalides are more common for antimony than for arsenic and phosphorus. Antimony trioxide dissolves in concentrated acid to form oxoantimonyl compounds such as SbOCl and.
Antimonides, hydrides, and organoantimony compounds
Compounds in this class generally are described as derivatives of. Antimony forms antimonides with metals, such as indium antimonide and silver antimonide. The alkali metal and zinc antimonides, such as and, are more reactive. Treating these antimonides with acid produces the highly unstable gas stibine, :Stibine can also be produced by treating salts with hydride reagents such as sodium borohydride. Stibine decomposes spontaneously at room temperature. Because stibine has a positive heat of formation, it is thermodynamically unstable and thus antimony does not react with hydrogen directly.
Organoantimony compounds are typically prepared by alkylation of antimony halides with Grignard reagents. A large variety of compounds are known with both Sb and Sb centers, including mixed chloro-organic derivatives, anions, and cations. Examples include triphenylstibine and pentaphenylantimony.
History
,, was recognized in predynastic Egypt as an eye cosmetic as early as about 3100 BC, when the cosmetic palette was invented.An artifact, said to be part of a vase, made of antimony dating to about 3000 BC was found at Telloh, Chaldea, and a copper object plated with antimony dating between 2500 BC and 2200 BC has been found in Egypt. Austen, at a lecture by Herbert Gladstone in 1892, commented that "we only know of antimony at the present day as a highly brittle and crystalline metal, which could hardly be fashioned into a useful vase, and therefore this remarkable 'find' must represent the lost art of rendering antimony malleable."
The British archaeologist Roger Moorey was unconvinced the artifact was indeed a vase, mentioning that Selimkhanov, after his analysis of the Tello object, "attempted to relate the metal to Transcaucasian natural antimony" and that "the antimony objects from Transcaucasia are all small personal ornaments." This weakens the evidence for a lost art "of rendering antimony malleable".
The Roman scholar Pliny the Elder described several ways of preparing antimony sulfide for medical purposes in his treatise Natural History, around 77 AD. Pliny the Elder also made a distinction between "male" and "female" forms of antimony; the male form is probably the sulfide, while the female form, which is superior, heavier, and less friable, has been suspected to be native metallic antimony.
The Greek naturalist Pedanius Dioscorides mentioned that antimony sulfide could be roasted by heating by a current of air. It is thought that this produced metallic antimony.
Antimony was frequently described in alchemical manuscripts, including the Summa Perfectionis of Pseudo-Geber, written around the 14th century. A description of a procedure for isolating antimony is later given in the 1540 book De la pirotechnia by Vannoccio Biringuccio, predating the more famous 1556 book by Agricola, De re metallica. In this context Agricola has been often incorrectly credited with the discovery of metallic antimony. The book Currus Triumphalis Antimonii, describing the preparation of metallic antimony, was published in Germany in 1604. It was purported to be written by a Benedictine monk, writing under the name Basilius Valentinus in the 15th century; if it were authentic, which it is not, it would predate Biringuccio.
The metal antimony was known to German chemist Andreas Libavius in 1615 who obtained it by adding iron to a molten mixture of antimony sulfide, salt and potassium tartrate. This procedure produced antimony with a crystalline or starred surface.
With the advent of challenges to phlogiston theory, it was recognized that antimony is an element forming sulfides, oxides, and other compounds, as do other metals.
The first discovery of naturally occurring pure antimony in the Earth's crust was described by the Swedish scientist and local mine district engineer in 1783; the type-sample was collected from the Sala Silver Mine in the Bergslagen mining district of Sala, Västmanland, Sweden.
Coins of antimony were issued in China's Guizhou in 1931; durability was poor, and minting was soon discontinued because of its softness and toxicity.