# Chemicals/Thoriums

Thorium is chemical element number 90 in the periodic table.

## Radiation

The decay chain on the right depicts that chain for thorium.
Thorium nuclei are susceptible to alpha decay because the strong nuclear force cannot overcome the electromagnetic repulsion between their protons. The alpha decay of $^{232}$Th initiates the 4n decay chain which includes isotopes with a mass number divisible by 4 (hence the name; it is also called the thorium series after its progenitor). This chain of consecutive alpha and beta decays begins with the decay of $^{232}$Th to $^{228}$Ra and terminates at $^{208}$Pb. Any sample of thorium or its compounds contains traces of these daughters, which are isotopes of thallium, lead, bismuth, polonium, radon, radium, and actinium. Natural thorium samples can be chemically purified to extract useful daughter nuclides, such as $^{212}$Pb, which is used in nuclear medicine for cancer therapy. $^{232}$Th 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 10$^{21}$ years and alpha decay predominates.

## Theoretical thorium

Def. "a chemical element (symbol Th) with atomic number 90" is called thorium.

## Metals

Thorium is a moderately soft, paramagnetic, bright silvery, radioactive, actinide metal. In the periodic table, it lies to the right of actinium, to the left of protactinium, and below cerium.
At room temperature and pressure, thorium crystallizes into a face-centered cubic lattice, where one thorium atom occupies each location of a black sphere in the diagram on the left.
At high temperature over 1360 °C thorium crystallizes into a body-centred cubic lattice.
At high pressure around 100 GPa thorium crystallizes into a body-centred tetragonal lattice.
Pure thorium is very ductile and, as normal for metals, can be cold-rolled, swaged, and drawn.
Thorium metal has a bulk modulus (a measure of resistance to compression of a material) of 54 GPa, about the same as tin's (58.2 GPa). Aluminium's is 75.2 GPa; copper's 137.8 GPa; and mild steel's is 160–169 GPa.
Thorium is about as hard as soft steel, so when heated it can be rolled into sheets and pulled into wire.
Thorium is nearly half as dense as uranium and plutonium and is harder than either of them.
It becomes superconductive below 1.4 K.
Thorium's melting point of 1750 °C is above both those of actinium (1227 °C) and protactinium (1568 °C). At the start of 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. (The f-electron count for thorium is a non-integer due to a 5f–6d overlap.) 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.
While einsteinium has been measured to have a lower density, this measurement was done on small, microgram-mass samples, and is likely because of the rapid self-destruction of the crystal structure caused by einsteinium's extreme radioactivity.
Thorium's boiling point of 4788 °C is the fifth-highest among all the elements with known boiling points, behind osmium, tantalum, tungsten, and rhenium; 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.}}

## Impurities

The properties of thorium vary widely depending on the degree of impurities in the sample. The major impurity is usually thorium dioxide (ThO$_2$); even the purest thorium specimens usually contain about a tenth of a percent of the dioxide. Experimental measurements of its density give values between 11.5 and 11.66 g/cm$^3$: these are slightly lower than the theoretically expected value of 11.7 g/cm$^3$ calculated from thorium's lattice parameters, perhaps due to microscopic voids forming in the metal when it is cast. These values lie between those of its neighbours actinium (10.1 g/cm$^3$) and protactinium (15.4 g/cm$^3$), part of a trend across the early actinides.

## Alloys

Thorium can form alloys 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 thorium nuclear reactors. Thorium forms eutectic mixtures with chromium and uranium, and it is completely miscible in both solid and liquid states with its lighter congener cerium.

## Isotopes

Four-fifths of the thorium present at Earth's formation has survived to the present. $^{232}$Th is the only isotope of thorium occurring in quantity in nature. Its stability is attributed to its closed nuclear shell with 142 neutrons. Thorium has a characteristic terrestrial isotopic composition, with atomic weight 232.0377(4). It is one of only three radioactive elements (along with protactinium and uranium) that occur in large enough quantities on Earth for a standard atomic weight to be determined.
| nuclide symbol | historic name | Z(p) | N(n) | isotopic mass (u) | half-life | decay mode(s) | daughter isotope(s) | nuclear spin | representative isotopic composition (mole fraction) |
| range of natural variation (mole fraction) |||
| $^{209}$Th | | 90 | 119 | 209.01772(11) | 7(5) ms [3.8(+69-15)] | | | 5/2-# | |
| $^{210}$Th | | 90 | 120 | 210.015075(27) | 17(11) ms [9(+17-4) ms] | α | $^{206}$Ra | 0+ | |
| $^{210}$Th | | 90 | 120 | 210.015075(27) | 17(11) ms [9(+17-4) ms] | β$^+$ (rare) | $^{210}$Ac | 0+ | |
| $^{211}$Th | | 90 | 121 | 211.01493(8) | 48(20) ms [0.04(+3-1) s] | α | $^{207}$Ra | 5/2-# | |
| $^{211}$Th | | 90 | 121 | 211.01493(8) | 48(20) ms [0.04(+3-1) s] | β$^+$ (rare) | $^{211}$Ac | 5/2-# | |
| $^{212}$Th | | 90 | 122 | 212.01298(2) | 36(15) ms [30(+20-10) ms] | α (99.7%) | $^{208}$Ra | 0+ | |
| $^{212}$Th | | 90 | 122 | 212.01298(2) | 36(15) ms [30(+20-10) ms] | β$^+$ (.3%) | $^{212}$Ac | 0+ | |
| $^{213}$Th | | 90 | 123 | 213.01301(8) | 140(25) ms | α | $^{209}$Ra | 5/2-# | |
| $^{213}$Th | | 90 | 123 | 213.01301(8) | 140(25) ms | β$^+$ (rare) | $^{213}$Ac | 5/2-# | |
| $^{214}$Th | | 90 | 124 | 214.011500(18) | 100(25) ms | α | $^{210}$Ra | 0+ | |
| $^{215}$Th | | 90 | 125 | 215.011730(29) | 1.2(2) s | α | $^{211}$Ra | (1/2-) | |
| $^{216}$Th | | 90 | 126 | 216.011062(14) | 26.8(3) ms | α (99.99%) | $^{212}$Ra | 0+ | |
| $^{216}$Th | | 90 | 126 | 216.011062(14) | 26.8(3) ms | β$^+$ (.006%) | $^{216}$Ac | 0+ | |
| $^{216m1}$Th | | 2042(13) keV | 2042(13) keV | 2042(13) keV | 137(4) µs | | | (8+) | |
| $^{216m2}$Th | | 2637(20) keV | 2637(20) keV | 2637(20) keV | 615(55) ns | | | (11-) | |
| $^{217}$Th | | 90 | 127 | 217.013114(22) | 240(5) µs | α | $^{213}$Ra | (9/2+) | |
| $^{218}$Th | | 90 | 128 | 218.013284(14) | 109(13) ns | α | $^{214}$Ra | 0+ | |
| $^{219}$Th | | 90 | 129 | 219.01554(5) | 1.05(3) µs | α | $^{215}$Ra | 9/2+# | |
| $^{219}$Th | | 90 | 129 | 219.01554(5) | 1.05(3) µs | β$^+$ (10$^{−7}$%) | $^{219}$Ac | 9/2+# | |
| $^{220}$Th | | 90 | 130 | 220.015748(24) | 9.7(6) µs | α | $^{216}$Ra | 0+ | |
| $^{220}$Th | | 90 | 130 | 220.015748(24) | 9.7(6) µs | EC (2×10$^{−7}$%) | $^{220}$Ac | 0+ | |
| $^{221}$Th | | 90 | 131 | 221.018184(10) | 1.73(3) ms | α | $^{217}$Ra | (7/2+) | |
| $^{222}$Th | | 90 | 132 | 222.018468(13) | 2.237(13) ms | α | $^{218}$Ra | 0+ | |
| $^{222}$Th | | 90 | 132 | 222.018468(13) | 2.237(13) ms | EC (1.3×10$^{−8}$%) | $^{222}$Ac | 0+ | |
| $^{223}$Th | | 90 | 133 | 223.020811(10) | 0.60(2) s | α | $^{219}$Ra | (5/2)+ | |
| $^{224}$Th | | 90 | 134 | 224.021467(12) | 1.05(2) s | α | $^{220}$Ra | 0+ | |
| $^{224}$Th | | 90 | 134 | 224.021467(12) | 1.05(2) s | β$^+$β$^+$ (rare) | $^{224}$Ra | 0+ | |
| $^{225}$Th | | 90 | 135 | 225.023951(5) | 8.72(4) min | α (90%) | $^{221}$Ra | (3/2)+ | |
| $^{225}$Th | | 90 | 135 | 225.023951(5) | 8.72(4) min | EC (10%) | $^{225}$Ac | (3/2)+ | |
| $^{226}$Th | | 90 | 136 | 226.024903(5) | 30.57(10) min | α | $^{222}$Ra | 0+ | |
| $^{227}$Th | Radioactinium | 90 | 137 | 227.0277041(27) | 18.68(9) d | α | $^{223}$Ra | 1/2+ | Trace |
| $^{228}$Th | Radiothorium | 90 | 138 | 228.0287411(24) | 1.9116(16) a | α | $^{224}$Ra | 0+ | Trace |
| $^{228}$Th | Radiothorium | 90 | 138 | 228.0287411(24) | 1.9116(16) a | CD (1.3×10$^{−11}$%) | $^{208}$Pb $^{20}$O | 0+ | Trace |
| $^{229}$Th | | 90 | 139 | 229.031762(3) | 7.34(16)×10$^3$ a | α | $^{225}$Ra | 5/2+ | |
| $^{229m}$Th | | 0.0076(5) keV | 0.0076(5) keV | 0.0076(5) keV | 70(50) h | IT | $^{229}$Th | 3/2+ | |
| $^{230}$Th | Ionium | 90 | 140 | 230.0331338(19) | 7.538(30)×10$^4$ a | α | $^{226}$Ra | 0+ | Trace |
| $^{230}$Th | Ionium | 90 | 140 | 230.0331338(19) | 7.538(30)×10$^4$ a | CD (5.6×10$^{−11}$%) | $^{206}$Hg $^{24}$Ne | 0+ | Trace |
| $^{230}$Th | Ionium | 90 | 140 | 230.0331338(19) | 7.538(30)×10$^4$ a | SF (5×10$^{−11}$%) | (Various) | 0+ | Trace |
| $^{231}$Th | Uranium Y | 90 | 141 | 231.0363043(19) | 25.52(1) h | β$^−$ | $^{231}$Pa | 5/2+ | Trace |
| $^{231}$Th | Uranium Y | 90 | 141 | 231.0363043(19) | 25.52(1) h | α (10$^{−8}$%) | $^{227}$Ra | 5/2+ | Trace |
| $^{232}$Th | Thorium | 90 | 142 | 232.0380553(21) | 1.405(6)×10$^{10}$ a | α | $^{228}$Ra | 0+ | 1.0000 |
| $^{232}$Th | Thorium | 90 | 142 | 232.0380553(21) | 1.405(6)×10$^{10}$ a | β$^−$β$^−$ (rare) | $^{232}$U | 0+ | 1.0000 |
| $^{232}$Th | Thorium | 90 | 142 | 232.0380553(21) | 1.405(6)×10$^{10}$ a | SF (1.1×10$^{−9}$%) | (various) | 0+ | 1.0000 |
| $^{232}$Th | Thorium | 90 | 142 | 232.0380553(21) | 1.405(6)×10$^{10}$ a | CD (2.78×10$^{−10}$%) | $^{182}$Yb $^{26}$Ne $^{24}$Ne | 0+ | 1.0000 |
| $^{233}$Th | | 90 | 143 | 233.0415818(21) | 21.83(4) min | β$^−$ | $^{233}$Pa | 1/2+ | |
| $^{234}$Th | Uranium X1 | 90 | 144 | 234.043601(4) | 24.10(3) d | β$^−$ | $^{234m}$Pa | 0+ | Trace |
| $^{235}$Th | | 90 | 145 | 235.04751(5) | 7.2(1) min | β$^−$ | $^{235}$Pa | (1/2+)# | |
| $^{236}$Th | | 90 | 146 | 236.04987(21)# | 37.5(2) min | β$^−$ | $^{236}$Pa | 0+ | |
| $^{237}$Th | | 90 | 147 | 237.05389(39)# | 4.8(5) min | β$^−$ | $^{237}$Pa | 5/2+# | |
| $^{238}$Th | | 90 | 148 | 238.0565(3)# | 9.4(20) min | β$^−$ | $^{238}$Pa | 0+ | |
* ↑ Bold for nuclides with half-lives longer than the age of the universe (nearly stable)
* ↑ Abbreviations: CD: Cluster decay EC: Electron capture IT: Isomeric transition SF: Spontaneous fission
* ↑ Bold for stable isotopes
* 1 2 Intermediate decay product of $^{235}$U
* ↑ Intermediate decay product of $^{232}$Th
* ↑ Used in Uranium-thorium dating
* 1 2 Intermediate decay product of $^{238}$U
* ↑ Primordial radionuclide

## Hypotheses

* Thorium can be fissioned and fusioned.