Polonium (Po)
Polonium (Po) is a rare, highly radioactive element classified under the chalcogen family, which includes oxygen and sulfur. Discovered in 1898 by physicists Marie and Pierre Curie while studying pitchblende, polonium was named to honor Poland, a nod to Marie's heritage amidst its lack of independence at the time. Known for having the most isotopes of any element, polonium-210 is the most common and useful, characterized by a short half-life of approximately 138 days and potent alpha-emitting properties.
This element has significant physical characteristics, including a metallic, silvery-gray appearance and a melting point of 254 degrees Celsius. While polonium is extremely dangerous—over one hundred billion times more toxic than hydrogen cyanide—its natural occurrence is rare, primarily found in very small concentrations in uranium ore. Applications of polonium range from its historical use in atomic bomb development during World War II to modern uses in thermoelectric power systems and static electricity elimination in textiles.
However, due to its high toxicity and ability to induce cancer, polonium must be handled with extreme care. Its presence has even been detected in tobacco smoke, raising health concerns for smokers. Overall, polonium is a fascinating yet perilous element, reflecting the dual-edged nature of scientific discovery and its implications for human health and safety.
Polonium (Po)
- Element Symbol: Po
- Atomic Number: 84
- Atomic Mass: 209
- Group # in Periodic Table: 16
- Group Name: Disputed information
- Period in Periodic Table: 6
- Block of Periodic Table: p-block
- Discovered by: Marie Curie (1898)
Polonium is a rare, radioactive element of the periodic table. It is also sometimes referred to as "radium F." Polonium is a member of the chalcogen family, which also includes oxygen, sulfur, tellurium, and selenium. Polonium is the heaviest element in the chalcogen family. The classification of polonium is oftentimes disputed; it is considered to be semimetallic, usually categorized as either a post-transition metal or a metalloid based on its location in the periodic table.
Polonium is a highly radioactive element that was discovered in 1898 in France. The famous physicists Marie and Pierre Curie discovered the element while they were studying the properties of the mineral pitchblende. In addition to discovering the element, the Curies also coined the term "radioactive." After removing uranium and thorium from pitchblende, the Curies found the mineral was more radioactive than both elements combined. This necessitated the search for more radioactive elements and the ultimate discovery of polonium. The Curies named the element polonium after Marie’s native country of Poland, which was not recognized as an independent country in 1898. Marie Curie hoped that by giving the element this name, more attention might be paid to Polish independence efforts. Five months after they discovered polonium, the Curies famously isolated another radioactive element, radium.
Physical Properties
Polonium has a metallic, silvery-gray color. Its standard state at 298 kelvins (K) is solid. Polonium has a specific gravity of 9.32. Specific gravity of an element is the measurement of its density in comparison with that of water. Polonium is easily dissolved in dilute acids but is less soluble in alkalis. There are no common compounds of polonium, and any that exist are synthesized. The melting point of polonium is 254 degrees Celsius ((C). The boiling point of polonium is 962 (C. The specific heat of an element is the amount of energy required to raise the temperature by one degree. For polonium, at a temperature of 20 (C, the specific heat is 0.12 joules per gram (J/g).
Chemical Properties
Polonium’s chemical composition is similar to that of both bismuth and tellurium. Common oxidation states of polonium are +6, +4, and +2. Polonium has thirty-three known isotopes, more than any other element, all of which are radioactive and unstable. The most stable isotope of polonium is polonium-209, with a half-life of 102 years. However, the most common and useful of polonium’s isotopes is polonium-210, which has a half-life of 138.376 days. For this reason, polonium is a rare element in nature. Polonium-210 has a cubic crystal structure and is known as an alpha emitter. This means it undergoes alpha decay to produce alpha particles, which are two protons and two neutrons bonded together. As it breaks apart, polonium emits a large amount of radiation energy—140 watts per gram (W/g). Sometimes the element will appear to glow a bluish color, a visual by-product of the excitation of its surrounding gas.
Applications
Polonium is rarely found in nature because the half-life of all of its isotopes is comparatively very short. Three of its isotopes (polonium-210, polonium-214, and polonium-218) exist in the decay chain of uranium-238, an isotope of the element uranium. This means that polonium exists in uranium cores in the earth’s crust. Polonium is a very dangerous radioactive element—more than one hundred billion times more dangerous than hydrogen cyanide, an extremely toxic organic compound. However, the amount of polonium found in the earth’s crust is not enough to be harmful to humans.
Isolating polonium from natural sources is a particularly difficult endeavor. Polonium is only present in very small concentrations, which can make extracting it difficult and expensive. It is isolated with the use of a nuclear reactor. Inside the reactor, bismuth-209 is bombarded with neutrons, causing the isotope to decay. This forms a new isotope, bismuth-210, which has a very short half-life of five days. This in turn decays into polonium-210.
Polonium played an important role in the Dayton Project, an offshoot of the Manhattan Project, during World War II. Polonium was crucial in building neutron initiators for the atomic bombs. Along with beryllium, polonium was an ingredient in the "urchin" detonator of the bombs, which set off chain reactions. Polonium was present in the "Fat Man" bomb that fell on Nagasaki, Japan, in 1945.
Due to the heat radiation emitted by polonium, it has been used as a source of thermoelectric power. Its lightweight nature has made it a valuable heat supply aboard space satellites to keep electrical machinery warm in the cold temperatures of outer space. In addition, the alpha particles emitted by polonium have been useful in eliminating charges that cause static electricity. For this reason, polonium has been used in textile mills for reduction of static electricity in fabrics as well as to improve the clarity of pictures in photographic film.
Traces of polonium have also been found in tobacco smoke. Its presence can occur when tobacco leaves have been grown with phosphate fertilizers. Unfortunately, due to the toxic nature of the element, smokers that ingest polonium expose their cells to its harmful radiation. Between 1943 and 1947, the Atomic Energy Commission, in conjunction with the Manhattan Project, conducted experiments on the effects of polonium on humans. Five people participated in the experiments, which were held at the University of Rochester. Polonium has been found to increase the possibility of developing cancer and must be handled safely to reduce exposure to radiation.
Bibliography
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"Technical Data for Polonium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 4 June 2015.