Views: 0 Author: Site Editor Publish Time: 2023-02-23 Origin: Site
Naturally occurring tungsten consists of four stable isotopes (182W, 183W, 184W, and 186W) and one very long-lived radioactive isotope,180W.Theoretically,all five elements can decay into isotopes of element 72 (hafnium) through α emission,but only 180W decay has been observed so far,with a half-life of (1.8±0.2)×1018 years;averaged In other words,this produces approximately two 180W alpha decays per gram of native tungsten per year.This ratio corresponds to a specific activity of approximately 63 microbecquerels per kilogram.This decay rate is orders of magnitude lower than that observed in carbon or potassium found on Earth, which also contain small amounts of long-lived radioactive isotopes.Bismuth has long been considered non-radioactive,but 209 Bi (its longest-lived isotope) actually decays with a half-life of 2.01×1019 years or 10 times slower than 180.W.However, since the naturally occurring bismuth content is 100% 209.Bi,its specific activity is actually higher than natural tungsten,3 millibecquerels per kilogram. Other naturally occurring isotopes of tungsten have not been observed to decay,limiting their half-lives to at least 4 × 1021 years if they decay at all.Another 30 artificial radioactive isotopes of tungsten have been characterized,the most stable of which are 181W with a half-life of 121.2 days,185W with a half-life of 75.1 days,188W with a half-life of 69.4 days,178W with a half-life of 21.6 days, 187W with a half-life of 23.72 hours.The remaining radioisotopes all have a half-life of less than 3 hours,with most having a half-life of less than 8 minutes.Tungsten also has 11 elementary states,the most stable is 179mW (t1/2 6.4 minutes).
Tungsten is basically a non-reactive element:it does not react with water,is not attacked by most acids and bases,and does not react with oxygen or air at room temperature.At elevated temperatures (i.e. when hot),it reacts with oxygen to form tungsten (VI) trioxide,or WO3.However,it reacts directly with fluorine (F2) at room temperature to form the colorless gas tungsten(VI) fluoride (WF6).At about 250 °C,it reacts with chlorine or bromine and,at certain elevated temperatures,with iodine.Finely divided tungsten is pyrophoric.The most common oxidation state of tungsten is +6,but it exhibits all oxidation states from -2 to +6.Tungsten is usually combined with oxygen to form yellow tungsten oxide WO3,which dissolves in alkaline aqueous solution to form tungstate ion WO2−4.Tungsten carbide (W2C and WC) is produced by heating powdered tungsten and carbon.W2C is chemically resistant,although it reacts strongly with chlorine to form tungsten hexachloride (WCl6).In aqueous solution, tungstates produce heteropolyacids and polyoxometalate anions under neutral and acidic conditions.When tungstate is gradually treated with acid,it first produces the soluble,metastable "paratungstate A" anion, W7O6−24,converted to the less soluble "paratungstic acid B" anion over time,H2W12O10−42.Further acidification produces the highly soluble metatungstate anion, H2W12O6−40,after which equilibrium is reached.Metatungstate ions exist as symmetrical clusters of twelve tungsten-oxygen octahedra,called Keggin anions.Many other polyoxometalate anions exist in metastable forms.The inclusion of different atoms (such as phosphorus) in place of two central hydrogens in metatungstate produces a variety of heteropolyacids,such as phosphotungstic acid H3PW12O40.Tungsten trioxide can form intercalation compounds with alkali metals.These are known as bronzes;an example is sodium tungsten bronze.In gaseous form,tungsten forms the
diatomic species W2.These molecules have sixfold bonds between tungsten atoms the highest known bond order among stable atoms.
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