Atomic number 84 · Metalloid
Polonium Po
Polonium (Po), element 84, is an intensely radioactive element with no stable isotopes. It was the first element discovered by Marie and Pierre Curie and is lethally toxic in minute amounts. It is classified by some as a metalloid and by others as a metal.
Key properties
| Atomic number | 84 |
|---|---|
| Atomic weight | [209] (No stable isotope; mass number of a representative isotope in brackets) |
| Category | Metalloid |
| Group | 16 |
| Period | 6 |
| Block | p |
| State (25 °C, 1 atm) | Solid |
| Melting point | 527 K (253.9 °C) |
| Boiling point | 1235 K (961.9 °C) |
| Density | 9.32 g/cm³ |
| Electronegativity (Pauling) | 2 |
| Atomic radius (van der Waals) | 197 pm |
| First ionization energy | 8.417 eV |
| Electron affinity | 1.9 eV |
| Oxidation states | +4, +2 |
| Discovered | 1898 |
Electron configuration
- Condensed
- [Xe]6s2 4f14 5d10 6p4
- Full
- 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p4
- Electrons per shell
- 2 · 8 · 18 · 32 · 18 · 6
Orbital diagram
Position in the table
Discovery
In 1898 Marie and Pierre Curie in Paris noticed that pitchblende, a uranium ore, was far more radioactive than its uranium content could explain. Processing large quantities of ore chemically and following the radioactivity through each step, they announced in July a new element that separated together with bismuth. In December they announced radium.
Polonium is so scarce in ore, reportedly around 0.1 mg per tonne of uranium ore, that gathering a pure sample was extremely difficult. Marie Curie received the 1911 Nobel Prize in Chemistry for the discovery of polonium and radium.
Origin of the name
The element is named after Poland (Latin Polonia), Marie Curie's homeland, which at the time was partitioned among Russia, Prussia and Austria and did not exist as a state. The Curies hoped the name would draw attention to Poland's situation, and polonium is often described as the first element named with a political purpose.
Main uses
- Static eliminators: alpha particles from polonium-210 ionise the air, and it was used in devices that remove static charge in film and precision-manufacturing plants.
- Neutron sources: mixed with beryllium, polonium's alpha particles knock neutrons out of beryllium; such sources served as neutron initiators in early nuclear weapons.
- Heat sources: a gram of polonium-210 releases roughly 140 watts of heat, and it was used to keep equipment warm on the Soviet Lunokhod lunar rovers.
Isotopes
All isotopes of polonium are radioactive. The most familiar, polonium-210, has a half-life of about 138 days and is made today mainly by irradiating bismuth-209 with neutrons in a reactor. Polonium-209 and polonium-208 live longer, with half-lives of around a century and about 2.9 years respectively. Because polonium emits almost only alpha particles, a sheet of paper stops its radiation outside the body, but inside the body it is extremely dangerous.
In everyday life
The 2006 death of former Russian intelligence officer Alexander Litvinenko in London after polonium-210 poisoning showed the world how deadly this element is. Tobacco smoke contains traces of polonium-210, thought to come from radon decay products that settle on tobacco leaves, and it is discussed as one of the contributors to smoking-related lung damage. Polonium is also notable as one of the very few elements that crystallise in a simple cubic structure.
Good to know
- Polonium was the first element discovered by the Curies, in 1898.
- Polonium is one of very few elements with a simple cubic crystal structure.
- A gram of polonium-210 heats itself strongly through radioactive decay.
Same group (16)
Data sources · Properties: PubChem Periodic Table (US NIH/NLM public data) · Atomic weights: CIAAW 2024 abridged standard atomic weights · Names: Wikidata (CC0); Korean names follow the Korean Chemical Society. Retrieved 2026-09-23.