Polonium dioxide
Names | |
---|---|
Systematic IUPAC name
Polonium dioxide | |
Identifiers | |
ChemSpider | |
UNII | |
Properties | |
PoO2 | |
Molar mass | 240.98 g/mol[1] |
Appearance | pale yellow crystalline solid[1][2][3] |
Density | 8.9 g/cm3[1] |
Melting point | 500 °C (932 °F; 773 K) (decomposes)[1][2] sublimes at 885 °C (under oxygen)[2][4] |
Structure | |
fluorite, Pearson symbol cF12 | |
Fm3m (No 225) | |
a = 0.5637 nm[3]
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Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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
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]
Preparation
Polonium dioxide is prepared by reacting elemental polonium with oxygen at 250 °C or by thermal decomposition of
Chemistry
When placed in
Halogenation of polonium dioxide with the hydrogen halides yields the polonium tetrahalides:[2]
- PoO2 + 4 HF → PoF4 + 2 H2O
- PoO2 + 4 HCl → PoCl4 + 2 H2O
- PoO2 + 4 HBr → PoBr4 + 2 H2O
- PoO2 + 4 HI → PoI4 + 2 H2O
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]
The reaction of polonium dioxide with potassium hydroxide or potassium nitrate in air gives the colourless potassium polonite (K2PoO3):[6]
- PoO2 + 2 KOH → K2PoO3 + H2O
- PoO2 + 2 KNO3 → K2PoO3 + 2 NO
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
References
- ^ ISBN 978-1-4398-5511-9.
- ^ ISBN 0-12-352651-5
- ^ . Retrieved 12 June 2012.
- ^ ISBN 978-0-08-037941-8.
- ISBN 0-12-352651-5
- ^ ISBN 978-0-12-023604-6. Retrieved June 14, 2012.
- ISBN 978-0-618-85748-7. Retrieved June 14, 2012.