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Polonium

physical science Maturity 9-11 Next article →

Polonium is a rare and highly radioactive chemical element. It is identified by the symbol Po and the atomic number 84. Scientists sometimes classify it as a metalloid, which is a substance with properties between metals and non-metals. Chemically, it behaves similarly to the chalcogens selenium and tellurium. However, its metallic character is more like its neighbors thallium, lead, and bismuth. Polonium is unique because it has no stable isotopes. This means every version of the element is radioactive and will eventually decay into something else.

alpha po lattice
alpha po lattice

The most common form of polonium is polonium-210. This isotope is an alpha emitter, meaning it releases alpha particles during decay. It has a half-life of approximately 138.4 days. A half-life is the time required for half of a radioactive sample to decay. As polonium-210 decays, it transforms directly into a stable isotope called lead-206. This intense radioactivity causes several interesting effects. It can cause radiolysis, which is the breaking of chemical bonds by radiation. It also causes radioactive self-heating. If you have a few curies of polonium-210, it will emit a blue glow. This glow is caused by the ionization of the surrounding air.

Polonium exists in two different solid forms called allotropes. The alpha form is very special in the world of science. It is the only known example of a simple cubic crystal structure based on single atoms at standard temperature and pressure. The unit cell for this structure has an edge length of 335.2 picometers. The second form is the beta form, which has a rhombohedral structure. Polonium is also known to become airborne with surprising ease. Even though its boiling point is high, heating it in air can cause 50% of it to vaporize within 45 hours. Scientists suggest that alpha decay might knock small clusters of atoms off the surface.

alpha po lattice
alpha po lattice

Marie Skłodowska-Curie and Pierre Curie discovered polonium on July 18, 1898. They found it while investigating the radioactivity of pitchblende, a type of uranium ore. They noticed the pitchblende was more radioactive than the uranium and thorium it contained. This discovery led them to isolate polonium, making it the first element discovered through radioactivity alone. They named the element after Marie Curie's homeland, Poland. At the time, Poland was partitioned between three different countries and was not independent. The name was intended to draw political attention to Poland's lack of independence.

alpha po lattice
alpha po lattice

Finding polonium in nature is extremely difficult. It occurs only in tiny traces within uranium ores. For example, you might find only 0.1 mg of polonium per metric ton of ore. This is about 0.2% of the abundance of radium. Because it is so rare, most polonium is produced artificially today. Scientists produce it in milligram quantities through the neutron irradiation of bismuth. This involves hitting bismuth with high-energy neutrons or protons. Polonium-210 is much more powerful than other radioactive elements. One milligram of polonium-210 is 5,000 times more radioactive than radium.

alpha po lattice
alpha po lattice

Polonium has several specific and high-stakes applications. Its heat production makes it useful for heaters in space probes. It is also used in antistatic devices and as a source of neutrons and alpha particles. During World War II, polonium played a role in the Manhattan Project. It was a key ingredient in the 'Urchin' initiator. This device helped start the nuclear chain reaction in certain weapons. However, polonium is extremely dangerous to humans. Because of its high toxicity, it has been used as a poison in historical events, such as the poisoning of Alexander Litvinenko.

alpha po lattice
alpha po lattice

The chemistry of polonium is complex and often studied only on a trace scale. It dissolves easily in dilute acids but is only slightly soluble in alkalis. When polonium is in a solution, it might first appear pink due to Po2+ ions. However, the alpha radiation quickly ionizes the liquid and turns the ions into Po4+, making the solution yellow. Polonium also forms many synthetic compounds. The most stable are called polonides, which are made by reacting two elements together. There are more than 50 known polonium compounds, including various oxides, halides, and hydrides. These chemical properties connect polonium to the broader study of the periodic table and nuclear science.

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