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Polonium (Po)
Polonium (symbol Po) is the chemical element with atomic number 84: a post-transition metal, solid at 0 °C, radioactive, with an atomic mass of 209 u. Discovered in 1898 (Pierre and Marie Curie).
Polonium was the first element discovered through its radioactivity, by Marie and Pierre Curie in 1898. Its isotope polonium-210 gives off intense heat and emits alpha particles, harmless outside the body but devastating once swallowed. It is one of the most toxic substances known.
Key facts
- Atomic number
- 84
- Symbol
- Po
- French name
- Polonium
- Atomic mass
- 209 u
- Molar mass
- [209] g/mol
- Family
- Post-transition metals
- Position
- period 6, group 16, p-block
- State at 0 °C
- Solid
- Melting point
- 253.9 °C
- Boiling point
- 961.9 °C
- Density
- 9.2 g/cm³
- Electronegativity (Pauling)
- 2
- First ionization energy
- 812 kJ/mol
- Atomic radius
- 190 pm
- Electron configuration
- [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁴
- Abundance in Earth's crust
- 0 ppm (87th most abundant element)
- Indicative price
- 49,000 billion $/kg (order of magnitude)
- Radioactive
- yes
- Discovery
- 1898, Pierre and Marie Curie
Origin of the name
From Poland, Marie Curie's homeland.
What does polonium look like?
A silvery metal rarely seen in visible amounts. A sample of polonium-210 gives off a bluish glow, because its radiation excites the surrounding air, and it heats itself up.
Where is polonium found?
Present in minute traces in uranium ores, about 0.1 mg per tonne, as a link in the decay chain of uranium-238. It is also found in tobacco smoke, because it settles on the leaves.
Natural sources
- Pitchblende (uraninite), in traces
How is polonium produced?
It is made by irradiating bismuth-209 with neutrons in a nuclear reactor: it becomes bismuth-210, which decays into polonium-210. Virtually all world production, on the order of 100 g a year, comes from Russia.
Top producers
- Russia
What is polonium used for?
- Anti-static brushes for industry and photography.
- A heat source for spacecraft, such as the Soviet Lunokhod moon rovers.
- Neutron initiators in the first atomic bombs (with beryllium).
In everyday life
- An anti-static brush for lenses or photographic film (industrial use)
Role in living things
No biological role. It contributes to the radiation dose smokers receive and is thought to be one of the factors in smoking-related lung cancer.
Hazards of polonium
Extremely radiotoxic if swallowed or inhaled: a few micrograms can be fatal. Its alpha radiation, on the other hand, is stopped by a sheet of paper or the skin.
Cosmic origin
- None of it survives from the formation of the Solar System: it is constantly being created by the radioactive decay of uranium and thorium.
History of polonium
In July 1898, Marie and Pierre Curie, working through pitchblende, isolated a substance far more radioactive than uranium. Marie named it after her homeland, Poland, then wiped off the map and divided among Russia, Prussia and Austria: a political statement.
Did you know?
- In 2006, former Russian agent Alexander Litvinenko died in London after drinking tea laced with polonium-210.
- A single gram of polonium-210 gives off about 140 watts of heat.
- Radium, discovered by the Curies a few months later that same year, has overshadowed polonium in popular memory.
Isotopes of polonium
Polonium has no stable isotopes. Polonium-210, present in trace amounts in nature and in tobacco smoke, is one of the most toxic substances known.
- polonium-208: radioactive, half-life 2.9 years
- polonium-209: radioactive, half-life 124 years. The longest-lived isotope of polonium, used as a laboratory tracer.
- polonium-210: radioactive, half-life 138 days. A fearsome poison used to assassinate Alexander Litvinenko in 2006; also used to eliminate static electricity.
- polonium-214: radioactive, half-life 164 µs
- polonium-218: radioactive, half-life 3.1 min. The first daughter of radon-222, it irradiates the lungs when we breathe radon-laden air.
Related elements
Same family (post-transition metals): Aluminium (Al), Gallium (Ga), Indium (In), Tin (Sn), Thallium (Tl), Lead (Pb), Bismuth (Bi).
Same column (group 16): Oxygen (O), Sulfur (S), Selenium (Se), Tellurium (Te), Livermorium (Lv).