Editing Thorium (section)

==Bulk properties==
Thorium is a moderately soft, [[paramagnetism|paramagnetic]], bright silvery radioactive actinide metal that can be bent or shaped. In the [[periodic table]], it lies to the right of [[actinium]], to the left of [[protactinium]], and below [[cerium]]. Pure thorium is very [[Ductility|ductile]] and, as normal for metals, can be [[cold-rolling#Cold rolling|cold-rolled]], [[Swaging|swaged]], and [[Drawing (manufacturing)|drawn]].{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}} At room temperature, thorium metal has a [[Cubic crystal system|face-centred cubic]] crystal structure; it has two other forms, one at high temperature (over 1360&nbsp;°C; body-centred cubic) and one at high pressure (around 100&nbsp;GPa; [[tetragonal crystal system|body-centred tetragonal]]).{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}}

Thorium metal has a [[bulk modulus]] (a measure of resistance to compression of a material) of 54&nbsp;[[gigapascal|GPa]], about the same as [[tin]]'s (58.2&nbsp;GPa). [[Aluminium]]'s is 75.2&nbsp;GPa; copper's 137.8&nbsp;GPa; and mild steel's is 160–169&nbsp;GPa.<ref>{{cite book |last1=Gale |first1=W. F. |last2=Totemeier |first2=T. C. |title=Smithells Metals Reference Book |year=2003 |publisher=[[Butterworth-Heinemann]] |isbn=978-0-08-048096-1 |language=en |pages=15-2–15-3}}</ref> Thorium is about as hard as soft [[steel]], so when heated it can be rolled into sheets and pulled into wire.<ref name="Yu. D. Tretyakov">{{cite book|editor-first=Yu. D. |editor-last=Tretyakov|title= Non-organic chemistry in three volumes| publisher= Academy|date= 2007|volume= 3|series= Chemistry of transition elements|isbn= 978-5-7695-2533-9}}</ref>

Thorium is nearly half as dense as [[uranium]] and [[plutonium]] and is harder than both.<ref name="Yu. D. Tretyakov" /> Thorium has a magnetic susceptibility of 0.412 × 4π  × 10E-9 m<sup>3</sup> kg <sup>-1</sup> at room temperature. This susceptibility is mostly temperature-independent, however impurities and dopants can affect this value.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}} It becomes [[superconductor|superconductive]] below 1.4&nbsp;[[kelvin|K]].{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}} Thorium's [[melting point]] of 1750&nbsp;°C is above both those of actinium (1227&nbsp;°C) and protactinium (1568&nbsp;°C). At the start of [[period 7 element|period 7]], from [[francium]] to thorium, the melting points of the elements increase (as in other periods), because the number of delocalised electrons each atom contributes increases from one in francium to four in thorium, leading to greater attraction between these electrons and the metal ions as their charge increases from one to four. 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.<ref name="Yu. D. Tretyakov" /><ref name="Johansson" /> (The f-electron count for thorium metal is a non-integer due to a 5f–6d overlap.)<ref name="Johansson">{{cite journal |last1=Johansson |first1=B. |last2=Abuja |first2=R. |last3=Eriksson |first3=O. |last4=Wills |first4=J. M. |display-authors=3 |year=1995 |title=Anomalous fcc crystal structure of thorium metal. |journal=Physical Review Letters |volume=75 |issue=2 |pages=280–283 |doi=10.1103/PhysRevLett.75.280 |pmid=10059654 |bibcode=1995PhRvL..75..280J |url=https://zenodo.org/record/1233903 |archive-date=8 March 2023 |access-date=24 August 2019 |archive-url=https://web.archive.org/web/20230308191836/https://zenodo.org/record/1233903 |url-status=live }}</ref> 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. Thorium's boiling point of 4788&nbsp;°C is the fifth-highest among all the elements with known boiling points.{{efn|Behind [[osmium]], [[tantalum]], [[tungsten]], and [[rhenium]];{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}} higher boiling points are speculated to be found in the 6d transition metals, but they have not been produced in large enough quantities to test this prediction.{{Fricke1975}}}}

The properties of thorium vary widely depending on the degree of impurities in the sample. The major impurity is usually [[thorium dioxide]] ({{chem2|ThO2}}); even the purest thorium specimens usually contain about a tenth of a per cent of the dioxide.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}} Experimental measurements of its density give values between 11.5&nbsp;and&nbsp;11.66&nbsp;g/cm<sup>3</sup>: these are slightly lower than the theoretically expected value of 11.7&nbsp;g/cm<sup>3</sup> calculated from thorium's [[lattice parameter]]s, perhaps due to microscopic voids forming in the metal when it is cast.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}} These values lie between those of its neighbours actinium (10.1&nbsp;g/cm<sup>3</sup>) and protactinium (15.4&nbsp;g/cm<sup>3</sup>), part of a trend across the early actinides.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}}

Thorium can form [[alloy]]s with many other metals. Addition of small proportions of thorium improves the mechanical strength of [[magnesium]], and thorium-aluminium alloys have been considered as a way to store thorium in proposed future thorium nuclear reactors. Thorium forms [[eutectic mixture]]s with [[chromium]] and uranium, and it is completely [[miscibility|miscible]] in both solid and liquid [[state of matter|states]] with its lighter [[congener (chemistry)|congener]] cerium.{{sfn|Wickleder|Fourest|Dorhout|2006|pp=61–63}}