What is Polonium?
Polonium is a post-transition metal in in group 16, period 6 of the periodic table. It is radioactive and very rare on Earth because it has no stable isotopes. However, the decay of uranium produces polonium, so polonium can be found in trace amounts in minerals that contain uranium. Polonium has few practical uses, though it has been used in atomic bombs, poison, and aerospace technology.
Polonium’s Place in the Periodic Table
Group 16 elements are known as chalcogens. Oxygen, sulfur, selenium, tellurium, livermorium, and polonium make up this group. Polonium is unstable, so it readily decays into other elements. Therefore, it has no stable isotopes on Earth. Polonium is named after the discoverer’s place of birth, Polonia or Poland.
- Atomic number: 84
- Atomic Radius: 168 picometers
- Atomic mass: 209
- Symbol: Po
- Group: 16
- Period: 6
- Number of Protons: 84
- Number of Electrons: 84
- Number of Neutrons: 125
- Number of Isotopes: No natural isotopes
Properties of Polonium
Pure polonium is a silvery, grey, soft metal with an appearance similar to lead, which is also found in period 6. Because polonium is unstable, it is rare, but present in small quantities in uranium ores. On radioactive decay, polonium releases a nucleus of helium (2 protons and 2 neutrons) in a process known as alpha decay. This form of radiation is toxic if it enters the body through food or drink.
Polonium is solid at room temperature, and liquid up to 962 °C. That is about the temperature of molten rock, or lava, released from active volcanoes. Polonium has a density similar to a copper penny or a silver pendant.
- Melting Point: 254°C.
- Boiling Point: 962°C.
- Density of Solid Polonium: 2 g cm-3.
Polonium has six valence electrons (Fig3). However, it does not form chemical bonds in nature. Polonium and oxygen are both in group 16. When oxygen reacts with hydrogen, it forms water. When polonium reacts with hydrogen in the laboratory, it can produce PoH2. PoH2 and H2O are the only hydrides of group 16 elements that are liquid at room temperature. Even though polonium is solid at very high temperatures, if heated in air to 55°C, it will vaporize. 500 grams of polonium would be lost from a sample of 1000 grams exposed under these conditions after 45 days.
- Oxidation states: +6, +4, +2
- Specific Heat: Unknown
- Electronegativity: 2.0 (Pauling scale)
- Heat of Fusion: 13 kj mol-1
- Heat of Vaporization: 9 kj mol-1
- Electron Configuration: [Xe] 4f14 5d10 6s2 6p4
Due to radioactive decay with a Po-210 is very rare on Earth, and is mostly produced from the radioactive decay of uranium. Po-208 and Po-209 can be synthesized in a laboratory. Po-210 can be produced in the laboratory by collision of bismuth with neutrons. This is a process that occurs in the core of stars to produce heavier elements from lighter ones. These elements are then released into the universe during supernovas. In fact, all elements on the periodic table are thought to be formed this way after the Big Bang.
Alloys and Allotropes
Polonium is used to form an alloy with beryllium. When an alpha particle is released from polonium when it decays, it is captured by beryllium. Beryllium then releases a neutron. Therefore, polonium and beryllium are combined to create a source of neutrons.
Compounds of Polonium
Almost all compounds that contain polonium are produced in laboratories. One of the few naturally occurring polonium compounds is lead polonium. Because polonium decays to form lead, lead polonium eventually transforms to pure lead. Polonium hydride (PoH2) is a volatile liquid at room temperature. Beryllium and polonium were used as the switch to initiate the first atomic bomb.
Interesting Facts about Polonium
- Alpha particles released by polonium decay cannot penetrate skin. Therefore, it is not very harmful when outside the body, unless long-term, repeat exposure occurs. However, if consumed, it is toxic and can rapidly damage internal organs, leading to death.
- Polonium has been used by Russia to poison a former Russian spy that joined the British spy agency, MI6.
- Tobacco contains low amounts of polonium. It is estimated that polonium is responsible for 130 out of 1000 people that die from smoking.
Occurrence and Abundance of Polonium
Polonium is rare on Earth but can be found associated with ores of uranium. Uranium can be found in mineral sources, such as uraninite, carnotite, tyuyamunite, torbernite, and autunite. In an average sample of the Earth’s crust, for every kilogram of crust, .0000000002 g of Po are present. So, it is ten times more likely to buy a winning Mega Million lottery ticket than to find polonium in a handful of dirt.
Uses of Polonium
Most Notable Uses in General
There are few everyday uses of polonium. One use is to remove static electricity that is problematic during the production of fabrics, paper, and plastics. The positively charged alpha particles released by polonium decay can neutralize the static electricity produced by an excess of electrons.
Most Notable Uses in Science
Polonium has been used in specialized equipment by scientists. A gram of polonium will reach 500°C as a result of the energy released during radioactive decay. This heat has been used in space equipment as an energy source. This type of energy source was used on the first moon rovers deployed by Russia in 1970 and 1973.
Discovery of Polonium
Polonium was discovered by Marie and Pierre Curie in 1898. Marie Curie is well known for her work on radioactivity. After extracting uranium and thorium from uraninite, the Curies found that the remaining material was even more radioactive than uranium and thorium. They hypothesized that another radioactive element was present. They isolated a few milligrams of polonium from several tons of uranium ore.
Polonium in the Future
Most of the uses of polonium are historical. That is because alternatives that are more common and safer have been found. Presently, no new uses for this element have been discovered.