Editing Thorium (section)

===Inorganic compounds===
Most binary compounds of thorium with nonmetals may be prepared by heating the elements together.{{sfn|Greenwood|Earnshaw|1997|p=1267}} In air, thorium burns to form {{chem2|ThO2}}, which has the [[fluorite]] structure.<ref name="Yamashita">{{cite journal |title= Thermal expansions of NpO<sub>2</sub> and some other actinide dioxides |journal= J. Nucl. Mater. |volume= 245 |issue= 1 |date= 1997 |pages= 72–78 |last1= Yamashita |first1=Toshiyuki |last2= Nitani |first2=Noriko |last3= Tsuji |first3=Toshihide |last4= Inagaki |first4=Hironitsu| doi= 10.1016/S0022-3115(96)00750-7 |bibcode=1997JNuM..245...72Y}}</ref> Thorium dioxide is a [[refractory material]], with the highest melting point (3390&nbsp;°C) of any known oxide.<ref name="Emsley2011" /> It is somewhat [[hygroscopic]] and reacts readily with water and many gases;{{sfn|Wickleder|Fourest|Dorhout|2006|pp=70–77}} it dissolves easily in concentrated nitric acid in the presence of fluoride.{{sfn|Greenwood|Earnshaw|1997|p=1269}}

When heated in air, thorium dioxide emits intense blue light; the light becomes white when {{chem2|ThO2}} is mixed with its lighter homologue [[cerium dioxide]] ({{chem2|CeO2}}, ceria): this is the basis for its previously common application in [[gas mantle]]s.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=70–77}} A flame is not necessary for this effect: in 1901, it was discovered that a hot Welsbach gas mantle (using {{chem2|ThO2}} with 1% {{chem2|CeO2}}) remained at "full glow" when exposed to a cold unignited mixture of flammable gas{{which|date=November 2022}} and air.<ref name="Ivey" /> 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]]. It occurs because {{chem2|ThO2}} : Ce acts as a catalyst for the recombination of [[free radical]]s that appear in high concentration in a flame, whose deexcitation releases large amounts of energy. The addition of 1% cerium dioxide, as in gas mantles, heightens the effect by increasing emissivity in the visible region of the spectrum; but because cerium, unlike thorium, can occur in multiple oxidation states, its charge and hence visible emissivity will depend on the region on the flame it is found in (as such regions vary in their chemical composition and hence how oxidising or reducing they are).<ref name="Ivey" />

Several binary thorium [[chalcogen]]ides and oxychalcogenides are also known with [[sulfur]], [[selenium]], and [[tellurium]].{{sfn|Wickleder|Fourest|Dorhout|2006|pp=95–97}}

All four thorium tetrahalides are known, as are some low-valent bromides and iodides:{{sfn|Wickleder|Fourest|Dorhout|2006|pp=78–94}} the tetrahalides are all 8-coordinated hygroscopic compounds that dissolve easily in polar solvents such as water.{{sfn|Greenwood|Earnshaw|1997|p=1271}} Many related polyhalide ions are also known.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=78–94}} Thorium tetrafluoride has a [[monoclinic crystal system|monoclinic]] crystal structure like those of [[zirconium tetrafluoride]] and [[hafnium tetrafluoride]], where the {{chem2|Th(4+)}} ions are coordinated with {{chem2|F−}} ions in somewhat distorted [[square antiprism]]s.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=78–94}} The other tetrahalides instead have dodecahedral geometry.{{sfn|Greenwood|Earnshaw|1997|p=1271}} Lower iodides {{chem2|ThI3}} (black) and {{chem2|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 {{chem2|Th(4+)}} and could be more clearly formulated as [[electride]] compounds.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=78–94}} Many polynary halides with the alkali metals, [[barium]], thallium, and ammonium are known for thorium fluorides, chlorides, and bromides.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=78–94}} For example, when treated with [[potassium fluoride]] and [[hydrofluoric acid]], {{chem2|Th(4+)}} forms the complex anion {{chem2|[ThF6](2-)}} (hexafluorothorate(IV)), which precipitates as an insoluble salt, {{chem2|K2[ThF6]}} (potassium hexafluorothorate(IV)).<ref name="ekhyde" />

Thorium borides, carbides, silicides, and nitrides are refractory materials, like those of uranium and plutonium, and have thus received attention as possible [[nuclear fuel]]s.{{sfn|Greenwood|Earnshaw|1997|p=1267}} All four heavier [[pnictogen]]s ([[phosphorus]], [[arsenic]], [[antimony]], and bismuth) also form binary thorium compounds. Thorium germanides are also known.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=97–101}} Thorium reacts with hydrogen to form the thorium hydrides {{chem2|ThH2}} and {{chem2|Th4H15}}, the latter of which is superconducting below 7.5–8&nbsp;K; at standard temperature and pressure, it conducts electricity like a metal.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=64–66}} The hydrides are thermally unstable and readily decompose upon exposure to air or moisture.{{sfn|Greenwood|Earnshaw|1997|p=127}}

[[File:Uranocene-3D-balls.png|thumb|upright|alt=Structure of thorocene|Sandwich molecule structure of thorocene]]