1. He was a Norwegian priest and amateur mineralogist who studied the minerals in Telemark, where he served as vicar. Filtration of the remaining precipitates followed by addition of 47% sodium hydroxide results in the precipitation of thorium and uranium at about pH 5.8. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided. | EduRev Class 12 Question is … [93] Metallic thorium was isolated for the first time in 1914 by Dutch entrepreneurs Dirk Lely Jr. and Lodewijk Hamburger. It has been suggested as a replacement for uranium as nuclear fuel in nuclear reactors, and several thorium reactors have been built. With the later recognition that the rare earths were mostly trivalent and thorium was tetravalent, Mendeleev moved cerium and thorium to group IV in 1871, which also contained the modern carbon group (group 14) and titanium group (group 4), because their maximum oxidation state was +4. [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. Metallic thorium does have some f-character and this is thought to be the reason why it has an FCC crystalline structure, rather than the BCC structure of Ti, Zr, and Hf. After thorium, there is a new downward trend in melting points from thorium to plutonium, where the number of f electrons increases from about 0.4 to about 6: this trend is due to the increasing hybridisation of the 5f and 6d orbitals and the formation of directional bonds resulting in more complex crystal structures and weakened metallic bonding. The rare earths again precipitate out at higher pH. 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. DFT calculations have shown that 5f orbitals in the actinide complexes play a crucial role in stabilizing this fourth ligand by stabilizing both the s and p electrons of the two 2-coordinated hydrazonato ligands. The reason for this arrangement unlike other conventional electron configurations such as Na with configuration of [Ne]3s 2. It is more stable chemically than the now-common fuel uranium dioxide, because the latter oxidises to triuranium octoxide (U3O8), becoming substantially less dense. Although relatively little of those products are created as the result of the slow decay of thorium, a proper assessment of the radiological toxicity of 232Th must include the contribution of its daughters, some of which are dangerous gamma emitters,[159] and which are built up quickly following the initial decay of 232Th due to the absence of long-lived nuclides along the decay chain. Iwan. [89][90][91] Berzelius reused the name of the previous supposed element discovery[89][92] and named the source mineral thorite. Name: Thorium Symbol: Th Atomic Number: 90 Atomic Mass: 232.0381 amu Melting Point: 1750.0 °C (2023.15 K, 3182.0 °F) Boiling Point: 4790.0 °C (5063.15 K, 8654.0 °F) Number of Protons/Electrons: 90 Number of Neutrons: 142 Classification: Rare Earth Crystal Structure: Cubic Density @ 293 K: 11.72 g/cm 3 Color: silvery Atomic Structure Thorium was discovered in 1828 by the Norwegian amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jacob Berzelius, who named it after Thor, the Norse god of thunder. Also, the real electron configuration of an atom may differ from the prediction because of relativistic effects, shielding, etc. 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. [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. [60] Half sandwich compounds are also known, such as (η8-C8H8)ThCl2(THF)2, which has a piano-stool structure and is made by reacting thorocene with thorium tetrachloride in tetrahydrofuran. [150] 233Pa has a relatively long half-life of 27 days and a high cross section for neutron capture. Three atomic orbitals are theoretically available for the valence electrons to occupy: 5f, 6d, and 7s. The main nuclear power source in a reactor is the neutron-induced fission of a nuclide; the synthetic fissile[e] nuclei 233U and 239Pu can be bred from neutron capture by the naturally occurring quantity nuclides 232Th and 238U. [145], Thorium is more abundant than uranium, and can satisfy world energy demands for longer.[146]. [k] He determined that thorium was a very electropositive metal, ahead of cerium and behind zirconium in electropositivity. 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. Four-fifths of the thorium present at Earth's formation has survived to the present. The mixture is then cooled to 70 °C and diluted with ten times its volume of cold water, so that any remaining monazite sinks to the bottom while the rare earths and thorium remain in solution. International Atomic Energy Agency (2005). [1], Thorium nuclei are susceptible to alpha decay because the strong nuclear force cannot overcome the electromagnetic repulsion between their protons. Conversely, at temperatures below 200 °C the reaction does not go fast enough for the process to be practical. In natural thorium-containing waters, organic thorium complexes usually occur in concentrations orders of magnitude higher than the inorganic complexes, even when the concentrations of inorganic ligands are much greater than those of organic ligands. In the periodic table, it lies to the right of actinium, to the left of protactinium, and below cerium. Author information: (1)Unidade de Ciências Químicas e Radiofarmacêuticas, Instituto Tecnológico e Nuclear, 2686-953 Sacavém, Portugal. [48], When heated in air, thorium dioxide emits intense blue light; the light becomes white when ThO2 is mixed with its lighter homologue cerium dioxide (CeO2, ceria): this is the basis for its previously common application in gas mantles. [157] Internal exposure to thorium leads to increased risk of liver diseases. This appearance can also help advertise your publication. 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. Elements whose f orbital getting filled up by electrons are called f block elements. [Rn] 5f 14 6d 10 7s 2 7p 6 Keep in mind, electron configurations are most stable when they are filled or half-filled. This crystallises trisodium phosphate decahydrate when cooled below 60 °C; uranium impurities in this product increase with the amount of silicon dioxide in the reaction mixture, necessitating recrystallisation before commercial use. 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]. [78], In nature, thorium occurs in the +4 oxidation state, together with uranium(IV), zirconium(IV), hafnium(IV), and cerium(IV), and also with scandium, yttrium, and the trivalent lanthanides which have similar ionic radii. [49], Energy, some of it in the form of visible light, is emitted when thorium is exposed to a source of energy itself, such as a cathode ray, heat, or ultraviolet light. 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. To ensure that no precipitates form to block the reactive monazite surface, the mass of acid used must be twice that of the sand, instead of the 60% that would be expected from stoichiometry. 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. LFTRs run at atmospheric pressure instead of 150 to 160 times atmospheric pressure currently needed. This number of captures does not happen for 98–99% of the 232Th nuclei because the intermediate products 233U or 235U undergo fission, and fewer long-lived transuranics are produced. [29] Thorium oxide is being replaced in this use with other oxides, such as those of zirconium, cerium, and lanthanum. [44] In air, thorium burns to form ThO2, which has the fluorite structure. Thorium-232 is useful in breeder reactors because on capturing slow-moving neutrons it decays into fissionable uranium-233. Therefore the f electrons can not participate in the chemical bonding and the +3 oxidation number or state is common for lanthanides. 5f Elements in Periodic Table [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). In the case of Thorium the valence electrons is 4. For example, following alkaline digestion and the removal of phosphate, the resulting nitrato complexes of thorium, uranium, and the rare earths can be separated by extraction with tributyl phosphate in kerosene. 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. [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. [134] All substances emit energy (glow) at high temperatures, but the light emitted by thorium is nearly all in the visible spectrum, hence the brightness of thorium mantles. Laboratoire de Physique et Chimie des Nano‐objets, INSA, Université Paul Sabatier, 135 avenue de Rangueil, 31077 Toulouse Cedex (France), Fax: (+33) 561 559 697. [85] In 1824, after more deposits of the same mineral in Vest-Agder, Norway, were discovered, he retracted his findings, as the mineral (later named xenotime) proved to be mostly yttrium orthophosphate. [29] He published his findings in 1829, having isolated an impure sample by reducing KThF5 with potassium metal. Thorium, with an atomic number of 90, is the first element in the actinide series of the periodic table, the outer electrons of which are in the 5f, 6d, and 7s shells. Thorium Valence Electrons 4 Atomic Number 90 Learn more about the atomic number. [44] All four heavier pnictogens (phosphorus, arsenic, antimony, and bismuth) also form binary thorium compounds. [160] If a thorium-containing object has been chewed or sucked, it loses 0.4% of thorium and 90% of its dangerous daughters to the body. All elements from polonium (element 84) onward are measurably radioactive. [38], Thorium is a highly reactive and electropositive metal. [46] Thorium has no known biological role. Nature of the 5f electrons in the actinide series. [106], Up to the late 19th century, chemists unanimously agreed that thorium and uranium were analogous to hafnium and tungsten; the existence of the lanthanides in the sixth row was considered to be a one-off fluke. Results from difference in energy levels due to the fact that some orbitals fill in faster than others and explains why Actinides are transition metals. [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. [170] Thorium is especially common in the Tamil Nadu coastal areas of India, where residents may be exposed to a naturally occurring radiation dose ten times higher than the worldwide average. So it is 2 electrons. 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. First, sulfuric acid in excess of 60% of the sand mass is added, thickening the reaction mixture as products are formed. [116][117] In most countries, uranium was relatively abundant and the progress of thorium-based reactors was slow; in the 20th century, three reactors were built in India and twelve elsewhere. At 208Pb after the ingestion of thorium areCorrect answer is ' 0 ' with configuration thorium. Emitted can strike further 232Th nuclei, continuing the cycle a unique position on the surface dissolution recrystallisation. The Th4+ ion areCorrect answer is ' 0 ' organothorium compounds are also located the. 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