Thorium
Thorium is a chemical element with symbol Th and atomic number 90. A radioactive actinide metal, thorium is one of only two significantly radioactive elements that still occur naturally in large quantities as a primordial element (the other being uranium). It was discovered in 1828 by the Norwegian Reverend and amateur mineralogist Morten Thrane Esmark and identified by the Swedish chemist Jöns Jakob Berzelius, who named it after Thor, the Norse god of thunder.
At a glance
- Atomic number
- 90
- Atomic mass
- 232.03774 u
- Phase
- Solid
- Density
- 11.724 g/cm³
- Melting point
- 2,023 K
- Boiling point
- 5,061 K
- First ionization energy
- 608.5 kJ/mol
- Electronegativity
- 1.3
- Electron affinity
- 112.72 kJ/mol
- Molar heat capacity
- 26.23 J/(mol·K)
- Period
- 7
- Appearance
- silvery, often with black tarnish
Conditions and isotopes affect measured properties. Some properties of short-lived elements are predicted. Electronegativity uses the Pauling scale.
Thorium’s orbitals use a hydrogen-like approximation. Every orbital of each visible subshell is shown: in Shapes as the surface holding half its probability, with light and dark shades for opposite signs of the wavefunction; in Cloud as dots where its electrons are likely to be. Sizes are stepped by shell, like the Shell model.
86 is the [Rn] core total across six shells.
Preparing the orbital view…
90 protons142 neutrons
Thorium-232: its most common form in nature, or its longest-lived if it has none. The nucleus is drawn far too big: it’s about 100,000 times smaller than the atom.
Turn up the heat
A step of 1 K is the same size as 1 °C, so the two scales are always 273.15 apart. Fahrenheit is different: its degrees are smaller and it starts elsewhere, so water freezes at 273.15 K, 0 °C and 32 °F.25 °C · 77 °FSolid
At this temperature, thorium is a solid.
At normal atmospheric pressure (1 atm). The temperature scale is logarithmic. The particle box is schematic: real samples hold vastly more atoms, and spacing and speeds are not to scale.
Pull the electrons off
ThNeutral atom · no charge
A neutral thorium atom. Removing its first electron takes 609 kJ/mol.
Thorium’s outer shell holds 2 electrons. Electron 3 is the first from an inner shell: it sits closer to the nucleus with less shielding, so removing it takes 1.5× as much energy as the one before. Each dashed line on the chart marks another jump, into a shell even closer to the nucleus.
What does this tell us?
- Within a shell the steps rise gently. Each electron removed leaves fewer electrons pushing the others away, while the nucleus pulls just as hard, so the next one is held a little more tightly.
Show the values as a table
| Electron | Shell | Energy (kJ/mol) | × previous | Value |
|---|---|---|---|---|
| 1 | 7 | 609 | – | Measured |
| 2 | 7 | 1,168 | 1.9 | Measured |
| 3 | 6 | 1,768 | 1.5 | Estimated |
| 4 | 6 | 2,764 | 1.6 | Measured |
| 5 | 6 | 5,596 | 2 | Calculated |
| 6 | 6 | 6,667 | 1.2 | Calculated |
| 7 | 6 | 7,912 | 1.2 | Calculated |
| 8 | 6 | 9,166 | 1.2 | Calculated |
| 9 | 6 | 11,385 | 1.2 | Calculated |
| 10 | 6 | 12,833 | 1.1 | Calculated |
| 11 | 6 | 15,920 | 1.2 | Calculated |
| 12 | 6 | 17,464 | 1.1 | Calculated |
| 13 | 5 | 25,279 | 1.4 | Calculated |
| 14 | 5 | 27,498 | 1.1 | Calculated |
| 15 | 5 | 29,910 | 1.1 | Calculated |
| 16 | 5 | 32,419 | 1.1 | Calculated |
| 17 | 5 | 34,928 | 1.1 | Calculated |
| 18 | 5 | 37,533 | 1.1 | Calculated |
| 19 | 5 | 40,910 | 1.1 | Calculated |
| 20 | 5 | 43,515 | 1.1 | Calculated |
| 21 | 5 | 46,313 | 1.1 | Calculated |
| 22 | 5 | 49,015 | 1.1 | Calculated |
| 23 | 5 | 62,715 | 1.3 | Calculated |
| 24 | 5 | 65,610 | 1 | Calculated |
| 25 | 5 | 69,469 | 1.1 | Calculated |
| 26 | 5 | 72,364 | 1 | Calculated |
| 27 | 5 | 80,083 | 1.1 | Calculated |
| 28 | 5 | 83,942 | 1 | Calculated |
| 29 | 5 | 93,591 | 1.1 | Calculated |
| 30 | 5 | 97,450 | 1 | Calculated |
| 31 | 4 | 105,169 | 1.1 | Calculated |
| 32 | 4 | 111,923 | 1.1 | Calculated |
| 33 | 4 | 119,642 | 1.1 | Calculated |
| 34 | 4 | 126,396 | 1.1 | Calculated |
| 35 | 4 | 133,150 | 1.1 | Calculated |
| 36 | 4 | 140,869 | 1.1 | Calculated |
| 37 | 4 | 147,623 | 1 | Calculated |
| 38 | 4 | 154,377 | 1 | Calculated |
| 39 | 4 | 162,095 | 1 | Calculated |
| 40 | 4 | 169,814 | 1 | Calculated |
| 41 | 4 | 176,568 | 1 | Calculated |
| 42 | 4 | 184,287 | 1 | Calculated |
| 43 | 4 | 191,041 | 1 | Calculated |
| 44 | 4 | 198,760 | 1 | Calculated |
| 45 | 4 | 230,600 | 1.2 | Calculated |
| 46 | 4 | 236,871 | 1 | Calculated |
| 47 | 4 | 243,529 | 1 | Calculated |
| 48 | 4 | 250,669 | 1 | Calculated |
| 49 | 4 | 257,519 | 1 | Calculated |
| 50 | 4 | 264,080 | 1 | Calculated |
| 51 | 4 | 276,334 | 1 | Calculated |
| 52 | 4 | 283,184 | 1 | Calculated |
| 53 | 4 | 290,710 | 1 | Calculated |
| 54 | 4 | 297,754 | 1 | Calculated |
| 55 | 4 | 325,638 | 1.1 | Calculated |
| 56 | 4 | 332,392 | 1 | Calculated |
| 57 | 4 | 339,821 | 1 | Calculated |
| 58 | 4 | 346,672 | 1 | Calculated |
| 59 | 4 | 380,442 | 1.1 | Calculated |
| 60 | 4 | 388,353 | 1 | Calculated |
| 61 | 4 | 408,133 | 1.1 | Calculated |
| 62 | 4 | 416,141 | 1 | Estimated |
| 63 | 3 | 672,696 | 1.6 | Calculated |
| 64 | 3 | 687,940 | 1 | Calculated |
| 65 | 3 | 704,246 | 1 | Calculated |
| 66 | 3 | 721,710 | 1 | Calculated |
| 67 | 3 | 738,113 | 1 | Calculated |
| 68 | 3 | 753,550 | 1 | Calculated |
| 69 | 3 | 789,250 | 1 | Calculated |
| 70 | 3 | 805,653 | 1 | Calculated |
| 71 | 3 | 824,950 | 1 | Calculated |
| 72 | 3 | 841,352 | 1 | Calculated |
| 73 | 3 | 889,595 | 1.1 | Calculated |
| 74 | 3 | 904,068 | 1 | Calculated |
| 75 | 3 | 920,470 | 1 | Calculated |
| 76 | 3 | 934,943 | 1 | Calculated |
| 77 | 3 | 1,041,077 | 1.1 | Calculated |
| 78 | 3 | 1,058,444 | 1 | Calculated |
| 79 | 3 | 1,094,144 | 1 | Calculated |
| 80 | 3 | 1,110,546 | 1 | Calculated |
| 81 | 2 | 2,321,437 | 2.1 | Calculated |
| 82 | 2 | 2,361,961 | 1 | Calculated |
| 83 | 2 | 2,406,344 | 1 | Calculated |
| 84 | 2 | 2,446,868 | 1 | Calculated |
| 85 | 2 | 2,837,634 | 1.2 | Calculated |
| 86 | 2 | 2,891,665 | 1 | Calculated |
| 87 | 2 | 2,960,170 | 1 | Calculated |
| 88 | 2 | 3,002,894 | 1 | Calculated |
| 89 | 1 | 11,876,476 | 4 | Calculated |
| 90 | 1 | 12,084,817 | 1 | Calculated |
Successive ionization energies of gas-phase atoms and ions from the NIST Atomic Spectra Database. Solid bars are measured; hatched bars were estimated from nearby measurements or calculated from quantum theory, as is usual for highly charged ions. Electrons are taken from the outermost shell first, a simplification: electrons in different subshells of the same shell also differ in energy. On the log scale each gridline is 10 times the one below.
How does it compare?
Density
11.7 g/cm³22nd highest of 99
Melting point
2,023 K17th highest of 96
Boiling point
5,061 K5th highest of 97
Electronegativity
1.334th lowest of 96
First ionization energy
609 kJ/mol40th lowest of 99
Elements 1–99 from the reference data; heavier elements are left out because only a few atoms have ever been made, so their bulk properties are predictions. First ionization energies come from NIST. Density uses a logarithmic scale, because gases are around a thousand times less dense than solids; gas densities are at 0 °C and 1 atm. Melting and boiling points are at normal pressure. Everyday temperatures and light sources in the pictures are approximate. Hover over a dot to see the element, or click it to compare.
Keep exploring
Explore the stories, imagery, and reference data in more depth. Properties with no value in the reference are marked unavailable.
- ThoriumRoyal Society of Chemistry
- ThoriumWikipedia
- Quantum numbers and electron configurationsPurdue
- Hydrogenic wavefunctionsNIST
- Ionization energiesNIST Atomic Spectra Database