Polonium dioxide (also known as polonium(IV) oxide) is a chemical compound with the formula PoO2. It is one of three oxides of polonium, the other two being polonium monoxide (PoO) and polonium trioxide (PoO3). It is a pale yellow crystalline solid at room temperature. Under lowered pressure (such as a vacuum), it decomposes into elemental polonium and oxygen at 500 °C. It is the most stable oxide of polonium and is an interchalcogen.[5]
Structure and appearance
At room temperature, polonium dioxide has a face-centered cubic (fluorite) crystal structure; upon heating to high temperatures, it crystallises in the tetragonal crystal system. The cubic form is pale yellow, while the tetragonal form is red. Polonium dioxide darkens upon heating, and is chocolate brown at its sublimation point, 885 °C.[2][3] The ionic radius of the Po4+ ion is 1.02 or 1.04 Å; thus, the ratio of the ionic radii Po4+ /O2− is about 0.73, the lower limit of stability for the cubic crystal system, allowing polonium dioxide to have two modifications. When freshly prepared, polonium dioxide is always in the tetragonal form, and changes to the cubic form after being left to stand or after being cooled strongly.[6]
Occurrence
Polonium dioxide does not occur naturally due to the scarcity of polonium in nature and the high temperatures (250 °C) required to form the dioxide.[2]
In reactions, polonium dioxide behaves very much like its homologue tellurium dioxide, forming Po(IV) salts; however, the acidic character of the chalcogen oxides decreases going down the group, and polonium dioxide and polonium(IV) hydroxide are much less acidic than their lighter homologues.[6] For example, SO2, SO3, SeO2, SeO3 and TeO3 are acidic, but TeO2 is amphoteric, and PoO2, while amphoteric, even shows some basic character.[7]
Polonium dioxide is closely related to the polonite anion (PoO2− 3), similar to the relationship between polonium trioxide and the polonate anion (PoO2− 4).
Applications
Polonium dioxide has no uses outside of basic research.[6]
Precautions
Polonium, whether in elemental form or as any polonium compound, such as polonium dioxide, is extremely radioactive. Thus PoO2 must be handled in a glove box. The glove box must further be enclosed in another box similar to the glove box, maintained at a slightly higher pressure than the first glove box to prevent the radioactive materials from leaking out. Gloves made of natural rubber do not provide sufficient protection against the radiation from polonium; surgical gloves are necessary. Neoprene gloves shield radiation from polonium better than natural rubber.[6]
^ abcdefghHolleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, p. 594, ISBN0-12-352651-5
^Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, p. 585, ISBN0-12-352651-5
^Ebbing, Darrell D.; Gammon, Steven D. (2009). General Chemistry (9 ed.). Boston: Houghton Mifflin Company. p. 320. ISBN978-0-618-85748-7. Retrieved June 14, 2012.