Plutonium
[Rn] 5f⁶ 7s² · 2 · 8 · 18 · 32 · 24 · 8 · 2
The element that changed the course of the twentieth century. Plutonium-239 fissions on thermal neutrons and breeds in any uranium reactor, while plutonium-238 keeps spacecraft warm for decades with no fuel at all.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 94
- Atomic mass
- 244 а.е.м. ≈
- Electron configuration
- [Rn] 5f⁶ 7s²
- Electrons per shell
- 2 · 8 · 18 · 32 · 24 · 8 · 2
- Block
- f-block
- Group
- no data
- Period
- 7
- Electronegativity (Pauling)
- 1.28
- Electronegativity (Allen)
- 1.28
- Atomic radius
- 243 pm
- Covalent radius
- 187 pm
- Van der Waals radius
- 243 pm
- Ionisation energy 1
- 584.7 kJ/mol
- Electron affinity
- -48.3 kJ/mol
- Common oxidation states
- +4
- Oxidation states
- +3, +4, +5, +6, +7, +8
Physical properties
- State at 25 °C
- solid
- Density
- 19.85 g/cm³
- Melting point
- 912.5 K · 639.4 °C
- Boiling point
- 3 505 K · 3 231.9 °C
- Speed of sound
- 2 260 m/s
Thermal properties
- Heat of fusion
- 2.82 kJ/mol
- Heat of vaporisation
- 333.5 kJ/mol
- Specific heat capacity
- 0.13 J/(g·K)
- Thermal conductivity
- 6.74 W/(m·K)
Mechanical properties
- Young's modulus
- 96 GPa
- Shear modulus
- 43 GPa
- Bulk modulus
- 55 GPa
- Poisson ratio
- 0.21
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 1 460 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- monoclinic
- Lattice constants
- a = 618.3 pm
Abundance
- In the crust
- does not occur
- In the ocean
- does not occur
- In the universe
- does not occur
- In the human body
- does not occur
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 238Pu | — | 87.71 yr | α |
| 239Pu | — | 24 111.96 yr | α |
| 244Pu | — | 80.81 Myr | α |
Plutonium-239, half-life 24 110 years, is the weapons and power isotope. Plutonium-238, half-life 87.7 years, gives 0.5 W per gram and runs space power sources.
Discovery
- Year of discovery
- 1940
- Discovered by
- Glenn Seaborg and colleagues
- Where
- Berkeley, USA
- Origin of the name
- after Pluto, the next body beyond Neptune
History
Seaborg, McMillan, Kennedy and Wahl synthesised plutonium at the end of 1940 on the Berkeley cyclotron. The discovery was classified until the end of the war; the Trinity test and the Nagasaki bomb were both plutonium.
Where it occurs
Traces in uranium ores. Effectively absent from nature.
How it is produced
By neutron irradiation of uranium-238 in a reactor and chemical separation. World stocks are measured in hundreds of tonnes.
Role in living things
No biological role. Plutonium deposits in bone and liver and is essentially never excreted.
Safety
The hazard is chiefly inhalation: alpha radiation inside the lung. The popular claim that plutonium is the most poisonous substance known is a large exaggeration; botulinum toxin is more toxic by many orders of magnitude.
Uses
- Nuclear weapons
- MOX fuel for power reactors
- Plutonium-238 in radioisotope thermoelectric generators: it powers the Voyagers, Cassini and the Perseverance rover
- Plutonium-powered pacemakers (historical)
Curiosities
- Voyager 1, launched in 1977, is still returning data on plutonium-238.
- Plutonium has six allotropes at ordinary pressure — more than any other element.
- Its density changes by a quarter between phases, which makes plutonium metallurgy a nightmare.
- Plutonium is named after Pluto, at the time still a planet.