Polonium
Atomic Data
| Atomic Number | 84 |
| Symbol | Po |
| Atomic Weight | 209 u |
| Density (STP) | 9.196 g/cm³ |
| Melting Point | 253.85 °C (527 K) |
| Boiling Point | 961.85 °C (1235 K) |
| Electronegativity | 2.0 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p4 |
| Oxidation States | +2, +4 |
| Phase at STP | Solid |
| Category | Metalloid |
| Period / Group | 6 / 16 |
| CAS Number | 7440-08-6 |
Electron Configuration
[Xe] 4f14 5d10 6s2 6p4
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| N | 4 | 4f | 14 | 60 |
| O | 5 | 5s | 2 | 62 |
| O | 5 | 5p | 6 | 68 |
| O | 5 | 5d | 10 | 78 |
| P | 6 | 6s | 2 | 80 |
| P | 6 | 6p | 4 | 84 |
| Total | 84 | 84 | ||
Isotopes of Polonium
Polonium has two naturally occurring stable isotopes. The most abundant is ²⁰⁹Po, comprising None% of all naturally occurring Polonium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Polonium-209 | ²⁰⁹Po | 84 | 125 | trace | Stable |
| Polonium-210 | ²¹⁰Po | 84 | 126 | trace | Stable |
Abundance & Occurrence
Polonium is present in Earth's crust at approximately trace amounts by mass and at approximately trace amounts by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Extreme radioactivity: Polonium-210, the most commonly available isotope, is an intense alpha emitter; internal contamination (ingestion, inhalation, wound absorption) delivers a very high localised radiation dose: it is one of the most acutely toxic substances known by mass.
- Internal dose hazard: The principal hazard is internal exposure; alpha particles are stopped by skin but cause severe radiation damage to internal organs if Po-210 is ingested or inhaled: even microgram quantities are potentially lethal.
- Containment requirements: All polonium work must take place in radiologically controlled areas with negative-pressure glove boxes; alpha-monitoring for air and surface contamination is mandatory.
- Litvinenko assassination: The 2006 poisoning of Alexander Litvinenko in London with Po-210: causing acute radiation syndrome and death: demonstrated the extreme lethality of internal Po-210 contamination and the difficulty of detecting alpha-emitter poisoning.
Polonium in the Real World
Real-World Uses
- Static eliminator devices: Polonium-210 (t½ = 138.4 d) alpha sources ionise air between two electrodes to neutralise static electricity, used in anti-static brushes for cleaning photographic negatives, optical discs, and film in print production.
- Spacecraft heating elements (historical): Po-210 was used as a compact heat source (Lunokhod lunar rovers, early RTGs) because its intense alpha emission generates heat in a very small mass; it has been largely replaced by plutonium-238 for long-duration missions.
- Scientific research: Polonium is studied as a model system for heavy post-transition metals and as a source of alpha particles in nuclear physics experiments; its chemistry in the astatine-bismuth region of the periodic table is of fundamental interest.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
Has polonium ever been used for anything?
Polonium-210 has been used as a static eliminator in photographic film handling (small amounts of Po-210 ionise surrounding air, neutralising static charges that attract dust). It was used in nuclear weapon triggers (as a neutron initiator when mixed with beryllium). Polonium has also been used in some spacecraft RTGs. All uses are extremely limited due to its intense radioactivity and toxicity.
How toxic is polonium?
Polonium-210 is one of the most acutely toxic substances known. It is an intense alpha emitter: while alpha particles do not penetrate skin from outside, if Po-210 is ingested or inhaled, it delivers a massive internal radiation dose to surrounding tissues. The lethal dose is estimated at less than 1 microgram when inhaled or ingested. Polonium-210 was used to poison the former FSB officer Alexander Litvinenko in London in 2006: the first confirmed case of nuclear terrorism against an individual.
How was polonium discovered?
Polonium was discovered in July 1898 by Marie and Pierre Curie while studying the radioactivity of uranium ore (pitchblende). They noticed the ore was far more radioactive than pure uranium, suggesting unknown radioactive elements were present. After laboriously processing tonnes of pitchblende, they isolated two new elements: polonium and radium. Marie Curie named polonium after her native Poland, then partitioned among foreign powers and seeking independence.
Why is polonium so intensely radioactive?
Polonium-210 has a half-life of only 138 days and decays entirely by alpha emission, releasing 5.3 MeV alpha particles. Because all decays occur within this short period, the activity per gram is enormous: about 166 terabecquerels per gram (166 trillion disintegrations per second). A lethal dose in mass terms is less than 1 microgram, but that microgram is generating about 166 billion alpha disintegrations per second inside the body.