Thorium (Th)

Silvery metal

Thorium is a weakly radioactive actinide being explored as a safer alternative to uranium for nuclear power, and with [Rn] 6d² 7s², thorium-232 (half-life 14 billion years) is four times more abundant than uranium. Thorium fuel cycles produce less long-lived transuranic waste and cannot easily be weaponized.

Key metrics

Density11.7g/cm³

Melting point2,115K

Boiling point5,061K

Electronegativity1.3Pauling

Discovery

1828discovered

Discovered by: Jöns Jakob Berzelius
Reactivity profile: Slowly oxidizes in air
Reactivity: Medium
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Rn]}\; \textcolor{#22c55e}{6_{d}^{2}}\; \textcolor{#ef4444}{7_{s}^{2}}

[Rn] 6d2 7s2

Wave function

\Psi_{\text{Th}} \approx \frac{1}{\sqrt{90!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{90}(\mathbf{r}_{90}) \right|

Probability density $|\Psi|^2$ across the Th valence shell.

Crystal structure

Face-Centered Cubic

Lattice constantsa = 1.00

Cell anglesα = β = γ = 90°

Coordination number12

Atoms per cell4

Atomic packing factor0.74

Physical properties

Atomic radius: 180 pm
Ionization energy: 587 kJ/mol
Electron affinity: 50 kJ/mol
Crystal structure: Face-centered cubic

Oxidation states

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

2115 K5061 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

401.9nmTh I (violet)Violet100%

443.2nmTh I (blue)Violet70%

538.0nmTh I (green)Green40%

Dominant line 401.9 nmRange 402–538 nmTransitions 3