[13][14] Thorium has a characteristic terrestrial isotopic composition, with atomic weight 232.0377(4). [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. [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. [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. These f-block chemical elements known as actinides because they appear after actinium. 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. [137] Since the 1920s, thoriated tungsten wires have been used in electronic tubes and in the cathodes and anticathodes of X-ray tubes and rectifiers. Magnetic separation follows, with a series of magnets of increasing strength. In particular, concentrations of atoms with high neutron capture cross-sections must be very low (for example, gadolinium concentrations must be lower than one part per million by weight). )[75] Its decay accounts for a gradual decrease of thorium content of the Earth: the planet currently has around 85% of the amount present at the formation of the Earth. [35], High coordination numbers are the rule for thorium due to its large size. [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. The most stable isotope, 232Th, has a half-life of 14.05 billion years, or about the age of the universe; it decays very slowly via alpha decay, starting a decay chain named the thorium series that ends at stable 208Pb. He noted impregnated traces of a white mineral, which he cautiously assumed to be an earth (oxide in modern chemical nomenclature) of an unknown element. Thorium metal is silvery and tarnishes black when exposed to air, forming the dioxide. The scheme has a range of several hundred thousand years. 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. [35][36], Despite the anomalous electron configuration for gaseous thorium atoms, metallic thorium shows significant 5f involvement. Because of this, thorium is a potentially attractive alternative to uranium in mixed oxide fuels to minimise the generation of transuranics and maximise the destruction of plutonium. [167][168][169], Thorium exists in very small quantities everywhere on Earth although larger amounts exist in certain parts: the average human contains about 40 micrograms of thorium and typically consumes three micrograms per day. 5f elements in periodic table . [138][139], Thorium dioxide is found in heat-resistant ceramics, such as high-temperature laboratory crucibles,[29] either as the primary ingredient or as an addition to zirconium dioxide. Thorium's atomic number is 90. [1], Thorium has three known nuclear isomers (or metastable states), 216m1Th, 216m2Th, and 229mTh. 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. [50], All four thorium tetrahalides are known, as are some low-valent bromides and iodides:[51] the tetrahalides are all 8-coordinated hygroscopic compounds that dissolve easily in polar solvents such as water. First, sulfuric acid in excess of 60% of the sand mass is added, thickening the reaction mixture as products are formed. The ions with 2 or 6 electrons in 5f orbitals are coloured in both the crystalline and in solution state due to f-f transition of electrons. They are concentrated, but of small size. 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