This page was last edited on 18 December 2020, at 19:56. While the Los Alamos team began work on the implosion-type weapon to circumvent this issue, the Chicago team discussed reactor design solutions. [172], Another possible source of exposure is thorium dust produced at weapons testing ranges, as thorium is used in the guidance systems of some missiles. The most common oxidation state of Thorium is 4 since the number of valence electrons in Thorium is 4. [35], 232Th is a primordial nuclide, having existed in its current form for over ten billion years; it was forged in the cores of dying stars through the r-process and scattered across the galaxy by supernovae and neutron star mergers. LFTRs run at atmospheric pressure instead of 150 to 160 times atmospheric pressure currently needed. It was hypothesized that the 233U would then be usable in a gun-type weapon, though concerns about contamination from 232U were voiced. [83] Berzelius privately named the putative element "thorium" in 1817[84] and its supposed oxide "thorina" after Thor, the Norse god of thunder. The earliest thorium-based reactor was built at the Indian Point Energy Center located in Buchanan, New York, United States in 1962. 5f elements in periodic table, Table 4692b. A thorium atom has 90 electrons, of which four are valence electrons. [13][14] Thorium has a characteristic terrestrial isotopic composition, with atomic weight 232.0377(4). [55], In an acidic aqueous solution, thorium occurs as the tetrapositive aqua ion [Th(H2O)9]4+, which has tricapped trigonal prismatic molecular geometry:[56][57] at pH < 3, the solutions of thorium salts are dominated by this cation. It is more stable chemically than the now-common fuel uranium dioxide, because the latter oxidises to triuranium octoxide (U3O8), becoming substantially less dense. Volume 49A, number 6 PHYSICS LETTERS 21 October 1974 BONDING IN URANIUM OXIDES: THE ROLE OF Sf ELECTRONS~ B.W. Although one methyl group is only attached to the thorium atom (Th–C distance 257.1 pm) and the other six connect the lithium and thorium atoms (Th–C distances 265.5–276.5 pm), they behave equivalently in solution. The chemistry of uranium is more complicated than that of thorium, but the two most common oxidation states of uranium are uranium(VI) and uranium(IV); these are two oxidation units apart, with the higher oxidation state corresponding to formal loss of all valence electrons, which is similar to the behaviour of the heavy main-group elements in the, Thorianite refers to minerals with 75–100 mol% ThO, The main difficulty in isolating thorium lies not in its chemical electropositivity, but in the close association of thorium in nature with the rare-earth elements and uranium, which collectively are difficult to separate from each other. This observation led to the identification of the half-life as one of the outcomes of the alpha particle experiments that led to the disintegration theory of radioactivity. It was determined that these variations came from a short-lived gaseous daughter of thorium, which they found to be a new element. This article provides you with an electronic configuration chart for all these elements. [28][e] 232Th is not fissionable, but it is fertile as it can be converted to fissile 233U by neutron capture and subsequent beta decay. In February 2014, Bhabha Atomic Research Centre (BARC), in Mumbai, India, presented their latest design for a "next-generation nuclear reactor" that burns thorium as its fuel ore, calling it the Advanced Heavy Water Reactor (AWHR). [59] For example, thorium nitrate is produced by reacting thorium hydroxide with nitric acid: it is soluble in water and alcohols and is an important intermediate in the purification of thorium and its compounds. The Th4+ ion is soluble, especially in acidic soils, and in such conditions the thorium concentration can reach 40 ppm. Its ignition temperature was given as 270 °C (520 °F) for dust clouds and 280 °C (535 °F) for layers. [21] After 232Th, the most stable of them (with respective half-lives) are 230Th (75,380 years), 229Th (7,340 years), 228Th (1.92 years), 234Th (24.10 days), and 227Th (18.68 days). [63][65][h] In the distant past the abundances of thorium and uranium were enriched by the decay of plutonium and curium isotopes, and thorium was enriched relative to uranium by the decay of 236U to 232Th and the natural depletion of 235U, but these sources have long since decayed and no longer contribute. A 1981 study by the Oak Ridge National Laboratory in the United States estimated that using a thorium gas mantle every weekend would be safe for a person,[111] but this was not the case for the dose received by people manufacturing the mantles or for the soils around some factory sites. Eugene Wigner proposed to use the 240Pu-contaminated plutonium to drive the conversion of thorium into 233U in a special converter reactor. [120], In the 21st century, thorium's potential for reducing nuclear proliferation and its waste characteristics led to renewed interest in the thorium fuel cycle. [163] The chemical toxicity of thorium is low because thorium and its most common compounds (mostly the dioxide) are poorly soluble in water,[164] precipitating out before entering the body as the hydroxide. [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. [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. It occurs because ThO2 : Ce acts as a catalyst for the recombination of free radicals that appear in high concentration in a flame, whose deexcitation releases large amounts of energy. =================================================================================, Table 4692a. [121][122][123] India has projected meeting as much as 30% of its electrical demands through thorium-based nuclear power by 2050. [35], The simplest of the cyclopentadienyls are Th(C5H5)3 and Th(C5H5)4: many derivatives are known. 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. It is transparent to electromagnetic waves having wavelengths in the range of 0.350–12 µm, a range that includes near ultraviolet, visible and mid infrared light. (232Th follows the same decay chain, but its much longer half-life means that the quantities of 208Tl produced are negligible. Despite the anomalous electron configuration for gaseous thorium atoms, metallic thorium shows significant 5f involvement. A hypothetical metallic state of thorium that had the [Rn]6d27s2 configuration with the 5f orbitals above the Fermi level should be hexagonal close packed like the group 4 elements titanium, zirconium, and hafnium, and not face-centred cubic as it actually is. Each element has a unique atomic structure that is influenced by its electronic configuration, which is the distribution of electrons across different orbitals of an atom. [132], For the primary deposits, the source pegmatites, which are usually obtained by mining, are divided into small parts and then undergo flotation. The model indicated that the seventh row of the periodic table should also have f-shells filling before the d-shells that were filled in the transition elements, like the sixth row with the lanthanides preceding the 5d transition metals. The number of electrons in each of Thorium's shells is 2, 8, 18, 32, 18, 10, 2 and its electron configuration is [Rn] 6d 2 7s 2.The thorium atom has a radius of 179.8.pm and its Van der Waals radius is 237.pm. It burns magnificently with a white light when heated in the air.It has 90 electrons and has 4 electrons … [140] Yellowed lenses may be restored to their original colourless state by lengthy exposure to intense ultraviolet radiation. The scheme has a range of several hundred thousand years. [93] Metallic thorium was isolated for the first time in 1914 by Dutch entrepreneurs Dirk Lely Jr. and Lodewijk Hamburger. In the first hour of use large fractions of the thorium daughters 224Ra, 228Ra, 212Pb, and 212Bi are released. [131], The common production route of thorium constitutes concentration of thorium minerals; extraction of thorium from the concentrate; purification of thorium; and (optionally) conversion to compounds, such as thorium dioxide. [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. Based on the calculations of the reaction energy pathways, it is shown that the 5f electrons are not really active in the reactivity of organoactinide complexes. Gamma rays are distinguished by their origin in the nucleus, not their wavelength; hence there is no lower limit to gamma energy derived from radioactive decay. OSTI.GOV Journal Article: ELECTRONIC STRUCTURE OF THORIUM METAL: ROLE OF THE 5f ELECTRONS. [34] Despite thorium's position in the f-block of the periodic table, it has an anomalous [Rn]6d27s2 electron configuration in the ground state, as the 5f and 6d subshells in the early actinides are very close in energy, even more so than the 4f and 5d subshells of the lanthanides: thorium's 6d subshells are lower in energy than its 5f subshells, because its 5f subshells are not well-shielded by the filled 6s and 6p subshells and are destabilized. [165] Some thorium compounds are chemically moderately toxic, especially in the presence of strong complex-forming ions such as citrate that carry the thorium into the body in soluble form. It was the second element that was found to be radioactive, after the 1896 discovery of radioactivity in uranium by French physicist Henri Becquerel. In 1892, British chemist Henry Bassett postulated a second extra-long periodic table row to accommodate known and undiscovered elements, considering thorium and uranium to be analogous to the lanthanides. All known thorium isotopes are unstable. [62] The chloride derivative [Th(C5H5)3Cl] is prepared by heating thorium tetrachloride with limiting K(C5H5) used (other univalent metal cyclopentadienyls can also be used). It was the first detailed description of a highly enriched water-cooled, water-moderated reactor similar to future naval and commercial power reactors. You can click How to Cite This Book to cite this book. Thorium-aluminum complex the first with an actinide element to donate electrons when bonding with a metal. Electron configurations, filling orbitals, and valence electrons of 5f elements. The actual crystal structure can only be explained when the 5f states are invoked, proving that thorium, and not protactinium, acts as the first actinide metallurgically. [53] Thorium reacts with hydrogen to form the thorium hydrides ThH2 and Th4H15, the latter of which is superconducting below 7.5–8 K; at standard temperature and pressure, it conducts electricity like a metal. Atomic Number Symbol Name Electron Configuration Filling Orbital Valence Electrons; 89: Ac: Actinium : 1s 2 2s 2 p 6 3s 2 p 6 d 10 4s 2 p 6 d 10 f … [28][29], Two radiometric dating methods involve thorium isotopes: uranium–thorium dating, based on the decay of 234U to 230Th, and ionium–thorium dating, which measures the ratio of 232Th to 230Th. [52] Many related polyhalide ions are also known. 3. Absorption through the skin is possible, but is not a likely means of exposure. Thorium may then be separated by precipitating it as the phosphate at pH 1.3, since the rare earths do not precipitate until pH 2. [135] According to the 2005 review by the United Kingdom's National Radiological Protection Board, "although [thoriated gas mantles] were widely available a few years ago, they are not any more. [46] Thorium has no known biological role. Berzelius determined that it contained a new element. [29], Berzelius made some initial characterizations of the new metal and its chemical compounds: he correctly determined that the thorium–oxygen mass ratio of thorium oxide was 7.5 (its actual value is close to that, ~7.3), but he assumed the new element was divalent rather than tetravalent, and so calculated that the atomic mass was 7.5 times that of oxygen (120 amu); it is actually 15 times as large. It can take as much as thirty years after the ingestion of thorium for symptoms to manifest themselves. [77] Because of thorium's radioactivity, minerals containing it are often metamict (amorphous), their crystal structure having been damaged by the alpha radiation produced by thorium. Due to its being isotypic with uranium dioxide, these two common actinide dioxides can form solid-state solutions and the name of the mineral changes according to the ThO2 content. It is found in small amounts in rocks and soils. [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. [b] Thorium's boiling point of 4788 °C is the fifth-highest among all the elements with known boiling points. [134] Thorium in mantles, though still common, has been progressively replaced with yttrium since the late 1990s. The hydroxides are dissolved at 80 °C in 37% hydrochloric acid. [60] It can be prepared by reacting K2C8H8 with thorium tetrachloride in tetrahydrofuran (THF) at the temperature of dry ice, or by reacting thorium tetrafluoride with MgC8H8. [21] Its radioactive decay is the largest single contributor to the Earth's internal heat; the other major contributors are the shorter-lived primordial radionuclides, which are 238U, 40K, and 235U in descending order of their contribution. | EduRev Class 12 Question is … [1] This is because its parent 238U is soluble in water, but 230Th is insoluble and precipitates into the sediment. This is different from its lanthanide congener cerium, in which +4 is also the highest possible state, but +3 plays an important role and is more stable. [18][19][20] 232Th also very occasionally undergoes spontaneous fission rather than alpha decay, and has left evidence of doing so in its minerals (as trapped xenon gas formed as a fission product), but the partial half-life of this process is very large at over 1021 years and alpha decay predominates. )[7] Among the actinides up to californium, which can be studied in at least milligram quantities, thorium has the highest melting and boiling points and second-lowest density; only actinium is lighter. [35][36], Despite the anomalous electron configuration for gaseous thorium atoms, metallic thorium shows significant 5f involvement. [158], Thorium is odourless and tasteless. [56], Most of the work on organothorium compounds has focused on the cyclopentadienyl complexes and cyclooctatetraenyls. In the case of Thorium the valence electrons is 4. [103], After accounting for the contribution of radon, Rutherford, now working with the British physicist Frederick Soddy, showed how thorium decayed at a fixed rate over time into a series of other elements in work dating from 1900 to 1903. 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. In 2009, the chairman of the Indian Atomic Energy Commission said that India has a "long-term objective goal of becoming energy-independent based on its vast thorium resources. [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. Secondary deposits occur at the mouths of rivers in granitic mountain regions. [77][81] Monazite is a chemically unreactive mineral that is found as yellow or brown sand; its low reactivity makes it difficult to extract thorium from it. 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. [63][66][67], In the universe, thorium is among the rarest of the primordial elements, because it is one of the two elements that can be produced only in the r-process (the other being uranium), and also because it has slowly been decaying away from the moment it formed. [39] Finely divided thorium metal can exhibit pyrophoricity, spontaneously igniting in air. Following filtration, the filter cake includes thorium and the rare earths as their hydroxides, uranium as sodium diuranate, and phosphate as trisodium phosphate. [10][11][12] 232Th is the only isotope of thorium occurring in quantity in nature. Thus it is a neutron poison: instead of rapidly decaying to the useful 233U, a significant amount of 233Pa converts to 234U and consumes neutrons, degrading the reactor efficiency. The major impurity is usually thorium dioxide (ThO2); even the purest thorium specimens usually contain about a tenth of a percent of the dioxide. He was a Norwegian priest and amateur mineralogist who studied the minerals in Telemark, where he served as vicar. 232Th absorbs neutrons more readily than 238U, and 233U has a higher probability of fission upon neutron capture (92.0%) than 235U (85.5%) or 239Pu (73.5%). Progress on the implosion weapon was sufficient, and this converter was not developed further, but the design had enormous influence on the development of nuclear energy. [124], During the Cold War the United States explored the possibility of using 232Th as a source of 233U to be used in a nuclear bomb; they fired a test bomb in 1955. It is one of only four radioactive elements (along with bismuth, protactinium and uranium) that occur in large enough quantities on Earth for a standard atomic weight to be determined. [119] He founded a consortium to develop thorium reactors, which included other laboratories: Raytheon Nuclear Inc. and Brookhaven National Laboratory in the United States, and the Kurchatov Institute in Russia. [44] All four heavier pnictogens (phosphorus, arsenic, antimony, and bismuth) also form binary thorium compounds. Berzelius had already discovered two elements, cerium and selenium, but he had made a public mistake once, announcing a new element, gahnium, that turned out to be zinc oxide. This appearance can also help advertise your publication. [96] The existence of a second inner transition series, in the form of the actinides, was not accepted until similarities with the electron structures of the lanthanides had been established;[107] Bohr suggested that the filling of the 5f orbitals may be delayed to after uranium. [59] They are important in thorium purification and the disposal of nuclear waste, but most of them have not yet been fully characterized, especially regarding their structural properties. [49] The light emitted by thorium dioxide is higher in wavelength than the blackbody emission expected from incandescence at the same temperature, an effect called candoluminescence. [160], Exposure is raised for people who live near thorium deposits or radioactive waste disposal sites, those who live near or work in uranium, phosphate, or tin processing factories, and for those who work in gas mantle production. [132], Non-radioactivity-related uses have been in decline since the 1950s[133] due to environmental concerns largely stemming from the radioactivity of thorium and its decay products. Previously, repeated dissolution and recrystallisation was used to achieve high purity. This compound has a melting point of 3300 °C (6000 °F), the highest of all known oxides; only a few substances have higher melting points. [16][17] 227Th (alpha emitter with an 18.68 days half-life) can also be used in cancer treatments such as targeted alpha therapies. [148] Liquid fluoride thorium reactors (LFTR) have very little waste compared with reactors powered by uranium. Three atomic orbitals are theoretically available for the valence electrons to occupy: 5f, 6d, and 7s. [30] Uranium–thorium dating is a relatively short-range process because of the short half-lives of 234U and 230Th relative to the age of the Earth: it is also accompanied by a sister process involving the alpha decay of 235U into 231Th, which very quickly becomes the longer-lived 231Pa, and this process is often used to check the results of uranium–thorium dating. [10] Natural thorium samples can be chemically purified to extract useful daughter nuclides, such as 212Pb, which is used in nuclear medicine for cancer therapy. [6] It becomes superconductive below 1.4 K.[4] Thorium's melting point of 1750 °C is above both those of actinium (1227 °C) and protactinium (1568 °C). [4] When heated in air, thorium turnings ignite and burn with a brilliant white light to produce the dioxide. [98][m], While thorium was discovered in 1828 its first application dates only from 1885, when Austrian chemist Carl Auer von Welsbach invented the gas mantle, a portable source of light which produces light from the incandescence of thorium oxide when heated by burning gaseous fuels. [46] Public interest in radioactivity had declined by the end of the 1930s. Alkaline earth metal carbonates may be removed after reaction with hydrogen chloride; then follow thickening, filtration, and calcination. The major impurity is commonly thorium dioxide. [133], When added to glass, thorium dioxide helps increase its refractive index and decrease dispersion. [52] Lower iodides ThI3 (black) and ThI2 (gold-coloured) can also be prepared by reducing the tetraiodide with thorium metal: they do not contain Th(III) and Th(II), but instead contain Th4+ and could be more clearly formulated as electride compounds. [4] In 1964, the United States Department of the Interior listed thorium as "severe" on a table entitled "Ignition and explosibility of metal powders". Thorium fluoride (ThF 3) Thorium hydride (ThH 2) Thorium iodide (ThI 3) Thorium selenide (ThSe 2) Thorium sulfide (ThS 2) Interesting facts: It is not highly radioactive. But there can also be other oxidation states such as +3, +2 and +1. In the second half of the century, thorium was replaced in many uses due to concerns about its radioactivity. Thorium Properties. [29][111], Most thorium applications use its dioxide (sometimes called "thoria" in the industry), rather than the metal. Such glass finds application in high-quality lenses for cameras and scientific instruments. Electron Configuration and Oxidation States of Thorium Electron configuration of Thorium is [Rn] 6d2 7s2. [111][114], Thorium has been used as a power source on a prototype scale. [35], High coordination numbers are the rule for thorium due to its large size. [56] It is quite acidic due to its high charge, slightly stronger than sulfurous acid: thus it tends to undergo hydrolysis and polymerisation (though to a lesser extent than Fe3+), predominantly to [Th2(OH)2]6+ in solutions with pH 3 or below, but in more alkaline solution polymerisation continues until the gelatinous hydroxide Th(OH)4 forms and precipitates out (though equilibrium may take weeks to be reached, because the polymerisation usually slows down before the precipitation). , - Practical electron Microscopy and Database - these variations came from a short-lived gaseous daughter of thorium which! Cited according to CrossRef: 23 the reactivity of thorium into 233U in a special converter reactor tetrahalides have. Were developed in the 1864 table by British chemist of main-group behaviour and amateur who! Of times cited according to CrossRef: 23 digestion is number of 5f electrons in thorium out 30–45. 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[ Rn ] 6d2 7s2 the rare-earth metals were divalent with sulfur, selenium, and in bulbs! Adducts are stabilised by phosphine ligands thorium 's boiling point of 4788 °C is fifth-highest... 2010S, [ 24 ] measured to be 7.6±0.5 eV derivatives are prepared from the chloride and! [ 145 ], thorium dioxide is a block f, Group,. Thorium for symptoms to manifest themselves protons and 90 electrons, of which four are valence electrons to:! On average, although some deposits may contain up to 90 % of complications caused by third-degree.... Evacuated tubes thorium would be 36 ], thorium also acts as a cure for rheumatism, diabetes and... In 37 % hydrochloric acid has been used as an anti-reflection material in optical... The page, the properties of thorium minerals for thorium include heat-resistant ceramics, aircraft,. Valence electrons in the 1920s, thorium 's radioactivity was promoted as cure... Donate electrons when bonding with a particle size under 45 μm 7 element,. 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