Chemical Properties
Polonium is a rare and highly radioactive silver-white metal (sometimes categorized as a metalloid). Polonium is chemically similar to tellurium, but also has some similarities to its neighbor bismuth. Polonium is soluble in dilute acids and slightly soluble in bases. Solutions of polonium first appear pink because of the Po2+ ion, but then rapidly turn yellow because the alpha decay of polonium ionizes the solvent and oxidizes the Po2+ to Po4+. Since polonium also releases alpha particles upon decay, this process is accompanied by bubbling, heat and light emission from laboratory glassware due to absorption of the alpha particles.
Physical properties
Most of the known chemistry of polonium is based on the naturally occurring radioactiveisotope polonium-210, which is a natural radioactive decay by-product of the uranium decayseries. Its melting point is 254°C, its boiling point is 962°C, and its density is 9.32g/cm3.
Po-210 is a strong emitter of alpha particles. One gram of Po-210 will produce about 140watts of energy, making it ideal as a lightweight thermoelectric power source for space vehicles.It has a half-life of 138.39 days.
Po-209, the most stable isotope of polonium, decays into lead-205 by alpha decay. It costsabout $3,000 per microcurie, which is a very small amount of polonium.
Isotopes
There are 41 isotopes of polonium. They range from Po-188 to Po-219. Allof them are radioactive with half-lives ranging from a few milliseconds to 102 years,the latter for its most stable isotope Po-209. Polonium is involved with several radioactivedecay series, including the actinium series, Po-211 and Po-215; the thoriumseries, Po-212 and Po-216; and the uranium decay series, Po-210, Po-214, and Po-218.
Origin of Name
Named for Poland, the native country of Marie Curie, who discovered
the element.
Occurrence
Polonium is found only in trace amounts in the Earth’s crust. In nature it is found inpitchblende (uranium ore) as a decay product of uranium. Because it is so scarce, it is usuallyartificially produced by bombarding bismuth-209 with neutrons in a nuclear (atomic) reactor,resulting in bismuth-210, which has a half-life of five days. Bi-210 subsequently decays intoPo-210 through beta decay. The reaction for this process is 209Bi(n,γ )210Bi → 210Po + β-. Onlysmall commercial milligram amounts are produced by this procedure.
Characteristics
Polonium is more metallic in its properties than the elements above it in group 16. It isthe only element in group 16 that is naturally radioactive. It is in a position on the periodictable of elements where it can be a metal, metalloid, or nonmetal. It is more often considereda metal because of its electrical conductivity decreases with an increase in temperature.
As an oxide, it is similar to the reddish color of tellurium oxide. Chemically, it behavessimilar to tellurium, lead, and bismuth.
Uses
There are not many uses for polonium. Probably the most important is as a source of alphaparticles (nuclei of helium atoms) and high-energy neutrons for research and radiation studies.It is also used to calibrate radiation-detection devices.
Polonium is used to eliminate static electricity in industrial processes, such as rolling outpaper, wire, or sheet metal in mills. Polonium is also sometimes used in “brushes” to removedust from photographic film and in the manufacturing of spark plugs that make ignition systemsin automobiles more efficient, particularly in extremely cold temperatures. It can also beused as a portable, low-level power source and, since polonium is fissionable, used in nuclearweapons and nuclear electric power plants.
Definition
A radioactive metallic element belonging to group 16 of the periodic table. It occurs in very minute quantities in uranium ores. Over 30 radioisotopes are known, nearly all alphaparticle emitters. Polonium is a volatile metal and evaporates with time. It is also strongly radioactive; a quantity of polonium quickly reaches a temperature of a few hundred degrees C because of the alpha emission. For this reason it has been used as a lightweight heat supply in space satellites. Symbol: Po; m.p. 254°C; b.p. 962°C; r.d. 9.32 (20°C); p.n. 84; stablest isotope 209Po (half-life 102 years).
Definition
polonium: Symbol Po. A rare radioactivemetallic element of group 16(formerly VIB) of the periodic table;a.n. 84; r.a.m. 210; r.d. 9.32; m.p.254°C; b.p. 962°C. The element occursin uranium ores to an extent ofabout 100 micrograms per 1000 kilograms.It has over 30 isotopes, morethan any other element. The longestlivedisotope is polonium-209 (halflife103 years). Polonium hasattracted attention as a possible heatsource for spacecraft as the energyreleased as it decays is 1.4×105J kg-1s-1. It was discovered by MarieCurie in 1898 in a sample of pitchblende.
Hazard
Even though polonium is a rare element, it is a very dangerous radiation source and shouldbe avoided.
Cigarette smoke contains a minute amount of polonium, along with many other carcinogenicchemicals, many of which can cause lung cancer. Over one hundred trace elements andcompounds have been identified in cigarette smoke besides polonium. Some examples arenicotine, cresol, carbon monoxide, pyridine, and the carcinogenic compound benzopyrene.
