Protactinium
[Rn] 5f² 6d¹ 7s² · 2 · 8 · 18 · 32 · 20 · 9 · 2
One of the rarest and most expensive natural elements. Protactinium is named for what it becomes: its decay produces actinium, so it is literally the parent of actinium.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 91
- Atomic mass
- 231.036 а.е.м.
- Electron configuration
- [Rn] 5f² 6d¹ 7s²
- Electrons per shell
- 2 · 8 · 18 · 32 · 20 · 9 · 2
- Block
- f-block
- Group
- no data
- Period
- 7
- Electronegativity (Pauling)
- 1.5
- Electronegativity (Allen)
- 1.14
- Atomic radius
- 243 pm
- Covalent radius
- 200 pm
- Van der Waals radius
- 243 pm
- Ionisation energy 1
- 568 kJ/mol
- Electron affinity
- 53.7 kJ/mol
- Common oxidation states
- +5
- Oxidation states
- +2, +3, +4, +5
Physical properties
- State at 25 °C
- solid
- Density
- 15.37 g/cm³
- Melting point
- 1 841 K · 1 567.9 °C
- Boiling point
- 4 300 K · 4 026.9 °C ≈
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 12.34 kJ/mol
- Heat of vaporisation
- 481 kJ/mol ≈
- Specific heat capacity
- 0.099 J/(g·K)
- Thermal conductivity
- 47 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 177 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 1.4 K
Crystal structure
- Crystal structure
- tetragonal
- Lattice constants
- a = 392.5 pm · c = 323.8 pm
Abundance
- In the crust
- 1.4·10⁻⁶ mg/kg
- In the ocean
- no data
- In the universe
- no data
- In the human body
- no data
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 231Pa | — | 32 766.16 yr | α |
| 233Pa | — | 26.97 d | β− |
Protactinium-231, half-life 32 760 years, is the main natural isotope; protactinium-233 is an intermediate in the thorium fuel cycle.
Discovery
- Year of discovery
- 1913
- Discovered by
- Kasimir Fajans and Oswald Göhring
- Where
- Germany
- Origin of the name
- the parent of actinium: its decay produces actinium
History
Fajans and Göhring found a short-lived isotope in 1913, and Hahn and Meitner isolated long-lived protactinium-231 in 1917. That work began the long collaboration that led to the discovery of nuclear fission.
Where it occurs
1.4·10⁻⁶ mg/kg of the crust. It occurs in uranium ores at roughly one protactinium atom per three million uranium atoms.
How it is produced
Recovered from uranium processing residues. Perhaps a hundred kilograms have been made in total; a 1961 British programme extracted 125 grams from 60 tonnes of waste.
Role in living things
No biological role.
Safety
Extremely radiotoxic and handled in glove boxes. Comparable to plutonium in hazard.
Uses
- Dating marine sediments and corals through the protactinium-231 / thorium-230 pair
- Research in nuclear physics and actinide chemistry
Curiosities
- The name means, literally, the parent of actinium.
- The 1961 British programme to extract 125 grams cost half a million pounds, which at the time made it among the most expensive substances on Earth.
- Protactinium-231 accumulates in a thorium reactor and needs separate handling.
- The protactinium-thorium pair dates marine sediments back some 250 000 years.