Thorium monoxide (thorium(II) oxide), is the binary oxide of thorium having chemical formula ThO. In the vapor phase, it is a diatomic molecule.
Gaseous (molecular) form
Laser ablation of thorium in the presence of oxygen produces vapor-phase thorium monoxide. Thorium monoxide molecules contain a highly polar covalent bond. The effective electric field between the two atoms has been calculated to be about 80 gigavolts per centimeter, one of the largest known internal effective electric fields.
Solid form
Simple combustion of thorium in air produces thorium dioxide. However, exposure of a thin film of thorium to low-pressure oxygen at medium temperature forms a rapidly growing layer of thorium monoxide under a more-stable surface coating of the dioxide.
At extremely high temperatures, thorium dioxide can convert to the monoxide either by a comproportionation reaction (equilibrium with liquid thorium metal) above 1,850 K (1,580 °C; 2,870 °F) or by simple dissociation (evolution of oxygen) above 2,500 K (2,230 °C; 4,040 °F).
- ThO2 Th(l) ⇌ 2 ThO(s)
- ThO2 → ThO(s) ½ O2
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