Polonium
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴ · 2 · 8 · 18 · 32 · 18 · 6
The first element discovered by Marie Skłodowska-Curie and one of the most radiotoxic substances known. Polonium-210 emits alpha particles so intensely that a gram of it self-heats to 500 °C.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 84
- Atomic mass
- 209 а.е.м. ≈
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴
- Electrons per shell
- 2 · 8 · 18 · 32 · 18 · 6
- Block
- p-block
- Group
- Chalcogens
- Period
- 6
- Electronegativity (Pauling)
- 2
- Electronegativity (Allen)
- 2.19
- Atomic radius
- 135 pm
- Covalent radius
- 140 pm
- Van der Waals radius
- 197 pm
- Ionisation energy 1
- 812.1 kJ/mol
- Electron affinity
- 183.3 kJ/mol
- Common oxidation states
- +2, +4
- Oxidation states
- -2, +2, +4, +5, +6
Physical properties
- State at 25 °C
- solid
- Density
- 9.196 g/cm³
- Melting point
- 527 K · 253.9 °C
- Boiling point
- 1 235 K · 961.9 °C
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- 13 kJ/mol
- Heat of vaporisation
- 103 kJ/mol
- Specific heat capacity
- 0.125 J/(g·K)
- Thermal conductivity
- 20 W/(m·K)
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- 26 GPa
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- 400 nΩ·m
- Magnetic ordering
- non-magnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- simple cubic
- Lattice constants
- a = 335.9 pm
Abundance
- In the crust
- 2·10⁻¹⁰ 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 |
|---|---|---|---|
| 209Po | — | 123.59 yr | α |
| 210Po | — | 138.43 d | α |
Polonium-210, half-life 138 days, is essentially the only isotope in use; it produces 140 watts of heat per gram.
Discovery
- Year of discovery
- 1898
- Discovered by
- Marie and Pierre Curie
- Where
- France
- Origin of the name
- after Poland, the homeland of Marie Skłodowska-Curie
History
Marie and Pierre Curie isolated polonium in 1898 from pitchblende after noticing that the residue was more radioactive than pure uranium. Marie named it after Poland, then partitioned between three empires.
Where it occurs
Around 10⁻¹⁰ mg/kg of the crust: polonium is made continuously in the uranium series and decays just as fast. Less than 100 grams exist naturally on the whole planet.
How it is produced
By neutron irradiation of bismuth-209 in a reactor. World output is about 100 grams a year.
Role in living things
No biological role. Polonium-210 is present in tobacco smoke and contributes measurably to a smoker's lung dose.
Safety
Among the most toxic substances per unit mass: an ingested lethal dose is measured in micrograms. Alpha radiation cannot cross skin, so the danger arises only on inhalation or ingestion.
Uses
- Antistatic brushes and ionisers in film and photographic manufacture
- Heat sources in spacecraft thermoelectric generators (historically)
- Neutron initiators in early nuclear weapon designs
Curiosities
- Polonium is named after a Poland that did not exist on the 1898 map — a deliberate political gesture.
- The 2006 polonium-210 poisoning was the first known murder by radioactive substance.
- Polonium is the only element with a simple cubic crystal structure at ordinary conditions.
- A gram of polonium-210 glows blue from ionising the air around it.