08 Ene 2021

Thanks to the reactivity of thorium with atmospheric oxygen and nitrogen, thorium also acts as a getter for impurities in the evacuated tubes. Thorium is also used to strengthen magnesium, coating tungsten wire in electrical equipment, controlling the grain size of tungsten in electric lamps, high-temperature crucibles, in glasses and used in camera and scientific instrument lenses. It can take as much as thirty years after the ingestion of thorium for symptoms to manifest themselves. Citing Literature Number of … [35], The simplest of the cyclopentadienyls are Th(C5H5)3 and Th(C5H5)4: many derivatives are known. The former (which has two forms, one purple and one green) is a rare example of thorium in the formal +3 oxidation state;[60][61] a formal +2 oxidation state occurs in a derivative. [4] These values lie between those of its neighbours actinium (10.1 g/cm3) and protactinium (15.4 g/cm3), part of a trend across the early actinides. [145], Thorium is more abundant than uranium, and can satisfy world energy demands for longer.[146]. All elements from polonium (element 84) onward are measurably radioactive. Since dissolution is very exothermic, the monazite sand cannot be added to the acid too quickly. [10], In deep seawaters the isotope 230Th makes up to 0.04% of natural thorium. Table 4692a. [162], Some nuclear safety agencies make recommendations about the use of thorium mantles and have raised safety concerns regarding their manufacture and disposal; the radiation dose from one mantle is not a serious problem, but that from many mantles gathered together in factories or landfills is. [46] This helps the compound remain solid in a flame, and it considerably increases the brightness of the flame; this is the main reason thorium is used in gas lamp mantles. The configuration goes in that order as well, just chop off the line breaks. [29][83][86][87], In 1828, Morten Thrane Esmark found a black mineral on Løvøya island, Telemark county, Norway. He commonly sent the most interesting specimens, such as this one, to his father, Jens Esmark, a noted mineralogist and professor of mineralogy and geology at the Royal Frederick University in Christiania (today called Oslo). In 1913, Danish physicist Niels Bohr published a theoretical model of the atom and its electron orbitals, which soon gathered wide acceptance. [134] Thorium in mantles, though still common, has been progressively replaced with yttrium since the late 1990s. Thorium, 90 Th Thorium; Pronunciation / ˈ θ ɔːr i ə m / (THOR-ee-əm) Appearance: silvery, often with black tarnish: Standard atomic weight A r, std (Th): 232.0377(4) Thorium in the periodic table [51] For example, when treated with potassium fluoride and hydrofluoric acid, Th4+ forms the complex anion ThF2−6, which precipitates as an insoluble salt, K2ThF6. the contrary the presence of narrow 5f localized unoccupied states is found in thorium and uranium containing glasses. [16][17] 227Th (alpha emitter with an 18.68 days half-life) can also be used in cancer treatments such as targeted alpha therapies. [46] It is somewhat hygroscopic and reacts readily with water and many gases;[47] it dissolves easily in concentrated nitric acid in the presence of fluoride. [146] A single neutron capture by 238U produces transuranic waste along with the fissile 239Pu, but 232Th only produces this waste after five captures, forming 237Np. He was a Norwegian priest and amateur mineralogist who studied the minerals in Telemark, where he served as vicar. It was hypothesized that the 233U would then be usable in a gun-type weapon, though concerns about contamination from 232U were voiced. Addition of small proportions of thorium improves the mechanical strength of magnesium, and thorium-aluminum alloys have been considered as a way to store thorium in proposed future thorium nuclear reactors. [30][31] Ionium–thorium dating is a related process, which exploits the insolubility of thorium (both 232Th and 230Th) and thus its presence in ocean sediments to date these sediments by measuring the ratio of 232Th to 230Th. [70], Thorium is the 41st most abundant element in the Earth's crust. An alloy of 90% platinum and 10% thorium is an effective catalyst for oxidising ammonia to nitrogen oxides, but this has been replaced by an alloy of 95% platinum and 5% rhodium because of its better mechanical properties and greater durability. [77] Allanite (chiefly silicates-hydroxides of various metals) can have 0.1–2% thorium and zircon (chiefly zirconium silicate, ZrSiO4) up to 0.4% thorium. [160] As the dangerous daughters of thorium have much lower melting points than thorium dioxide, they are volatilised every time the mantle is heated for use. They decompose slowly at room temperature. [158], Thorium is odourless and tasteless. 232Th is one of the three nuclides beyond bismuth (the other two being 235U and 238U) that have half-lives measured in billions of years; its half-life is 14.05 billion years, about three times the age of the earth, and slightly longer than the age of the universe. Thorium is a Block F, Group 3, Period 7 element. [21][i], Thorium only occurs as a minor constituent of most minerals, and was for this reason previously thought to be rare. [c], The properties of thorium vary widely depending on the degree of impurities in the sample. [54] The hydrides are thermally unstable and readily decompose upon exposure to air or moisture. Electron configurations, filling orbitals, and valence electrons of 5f elements. [166], In 1956, the Sylvania Electric Products explosion occurred during reprocessing and burning of thorium sludge in New York City, United States. In the first hour of use large fractions of the thorium daughters 224Ra, 228Ra, 212Pb, and 212Bi are released. [21] The International Union of Pure and Applied Chemistry (IUPAC) reclassified thorium as a binuclidic element in 2013; it had formerly been considered a mononuclidic element. [130] In 2014, world production of the monazite concentrate, from which thorium would be extracted, was 2,700 tonnes. Thorium dioxide has since been replaced in this application by rare-earth oxides, such as lanthanum, as they provide similar effects and are not radioactive.[133]. [132] Secondary materials (such as coastal sands) undergo gravity separation. In the 1950s, India targeted achieving energy independence with their three-stage nuclear power programme. Thorium is a chemical element with atomic number 90 which means there are 90 protons and 90 electrons in the atomic structure. [51] Many polynary halides with the alkali metals, barium, thallium, and ammonium are known for thorium fluorides, chlorides, and bromides. (232Th follows the same decay chain, but its much longer half-life means that the quantities of 208Tl produced are negligible. [157] Exposure to an aerosol of thorium, such as contaminated dust, can lead to increased risk of cancers of the lung, pancreas, and blood, as lungs and other internal organs can be penetrated by alpha radiation. Thorium forms eutectic mixtures with chromium and uranium, and it is completely miscible in both solid and liquid states with its lighter congener cerium. [46] Public interest in radioactivity had declined by the end of the 1930s. [132], Industrial production in the 20th century relied on treatment with hot, concentrated sulfuric acid in cast iron vessels, followed by selective precipitation by dilution with water, as on the subsequent steps. Then, fuming sulfuric acid is added and the mixture is kept at the same temperature for another five hours to reduce the volume of solution remaining after dilution. [133], When added to glass, thorium dioxide helps increase its refractive index and decrease dispersion. [150] 233Pa has a relatively long half-life of 27 days and a high cross section for neutron capture. [157] Thorium's low solubility in water also means that excretion of thorium by the kidneys and faeces is rather slow. In the 1920s, thorium's radioactivity was promoted as a cure for rheumatism, diabetes, and sexual impotence. Three atomic orbitals are theoretically available for the valence electrons to occupy: 5f, 6d, and 7s. [1] This is because its parent 238U is soluble in water, but 230Th is insoluble and precipitates into the sediment. This reflected the belief at that time that thorium and the rare-earth metals were divalent. It was also material in high-end optics and scientific instrumentation, used in some broadcast vacuum tubes, and as the light source in gas mantles, but these uses have become marginal. In these deposits, thorium is enriched along with other heavy minerals. [b] Thorium's boiling point of 4788 °C is the fifth-highest among all the elements with known boiling points. The concentration of the sulfuric acid is selected based on reaction rate and viscosity, which both increase with concentration, albeit with viscosity retarding the reaction. Tetrabenzylthorium, Th(CH2C6H5), and tetraallylthorium, Th(C3H5)4, are known, but their structures have not been determined. [160], Tests on the thorium uptake of workers involved in monazite processing showed thorium levels above recommended limits in their bodies, but no adverse effects on health were found at those moderately low concentrations. Thorium Properties. The chemical symbol for Thorium is Th. [35][36], Despite the anomalous electron configuration for gaseous thorium atoms, metallic thorium shows significant 5f involvement. Thus in elements electrons may occupy the $\mathrm{5f}$ or $\mathrm{6d}$ levels or sometimes both. [56], Most of the work on organothorium compounds has focused on the cyclopentadienyl complexes and cyclooctatetraenyls. [39] Finely divided thorium metal can exhibit pyrophoricity, spontaneously igniting in air. Thorium tetrafluoride is used as an anti-reflection material in multilayered optical coatings. 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