Polonium dioxide

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Polonium dioxide
Fluorite-unit-cell-3D-balls.png
Unit cell of cubic polonium dioxide (white = Po, yellow = O)
Names
Systematic IUPAC name
Polonium dioxide
Identifiers
ChemSpider
UNII
Properties
PoO2
Molar mass 240.98 g/mol [1]
Appearancepale 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]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Polonium dioxide (also known as polonium(IV) oxide) is a chemical compound with the formula Po O 2. 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]

Contents

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]

Preparation

Polonium dioxide is prepared by reacting elemental polonium with oxygen at 250 °C or by thermal decomposition of polonium(IV) hydroxide (PoO(OH)2), or various polonium salts such as polonium disulfate (Po(SO4)2), polonium selenate (Po(SeO4)2), or polonium tetranitrate (Po(NO3)4). [2] [4]

Chemistry

When placed in hydrogen, polonium dioxide is slowly reduced to metallic polonium at 200 °C; the same reduction occurs at 250 °C in ammonia or hydrogen sulfide. When heated in sulfur dioxide at 250 °C, a white compound is formed, possibly a polonium sulfite. [6] When polonium dioxide is hydrated, polonous acid (H2PoO3), a pale yellow, voluminous precipitate, is formed. Despite its name, polonous acid is an amphoteric compound, reacting with both acids and bases. [2] [4]

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 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]

Related Research Articles

<span class="mw-page-title-main">Hydroxide</span> Chemical compound

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, a ligand, a nucleophile, and a catalyst. The hydroxide ion forms salts, some of which dissociate in aqueous solution, liberating solvated hydroxide ions. Sodium hydroxide is a multi-million-ton per annum commodity chemical. The corresponding electrically neutral compound HO• is the hydroxyl radical. The corresponding covalently bound group –OH of atoms is the hydroxy group. Both the hydroxide ion and hydroxy group are nucleophiles and can act as catalysts in organic chemistry.

<span class="mw-page-title-main">Lead(II) oxide</span> Chemical compound

Lead(II) oxide, also called lead monoxide, is the inorganic compound with the molecular formula PbO. PbO occurs in two polymorphs: litharge having a tetragonal crystal structure, and massicot having an orthorhombic crystal structure. Modern applications for PbO are mostly in lead-based industrial glass and industrial ceramics, including computer components. It is an amphoteric oxide.

<span class="mw-page-title-main">Antimony trioxide</span> Chemical compound

Antimony(III) oxide is the inorganic compound with the formula Sb2O3. It is the most important commercial compound of antimony. It is found in nature as the minerals valentinite and senarmontite. Like most polymeric oxides, Sb2O3 dissolves in aqueous solutions with hydrolysis. A mixed arsenic-antimony oxide occurs in nature as the very rare mineral stibioclaudetite.

<span class="mw-page-title-main">Tellurium dioxide</span> Chemical compound

Tellurium dioxide (TeO2) is a solid oxide of tellurium. It is encountered in two different forms, the yellow orthorhombic mineral tellurite, β-TeO2, and the synthetic, colourless tetragonal (paratellurite), α-TeO2. Most of the information regarding reaction chemistry has been obtained in studies involving paratellurite, α-TeO2.

<span class="mw-page-title-main">Lead dioxide</span> Chemical compound

Lead(IV) oxide, commonly known as lead dioxide, is the inorganic compound with the formula PbO2. It is an oxide where lead is in an oxidation state of +4. It is a dark-brown solid which is insoluble in water. It exists in two crystalline forms. It has several important applications in electrochemistry, in particular as the positive plate of lead acid batteries.

<span class="mw-page-title-main">Selenium dioxide</span> Chemical compound

Selenium dioxide is the chemical compound with the formula SeO2. This colorless solid is one of the most frequently encountered compounds of selenium.

<span class="mw-page-title-main">Germanium monoxide</span> Chemical compound

Germanium monoxide (chemical formula GeO) is a chemical compound of germanium and oxygen. It can be prepared as a yellow sublimate at 1000 °C by reacting GeO2 with Ge metal. The yellow sublimate turns brown on heating at 650 °C. GeO is not well characterised. It is amphoteric dissolving in acids to form germanium(II) salts and in alkali to form "trihydroxogermanates" or "germanites" containing the Ge(OH)3− ion.

<span class="mw-page-title-main">Dinitrogen trioxide</span> Chemical compound

Dinitrogen trioxide is the chemical compound with the formula N2O3. It is one of the simple nitrogen oxides. It forms upon mixing equal parts of nitric oxide and nitrogen dioxide and cooling the mixture below −21 °C (−6 °F):

<span class="mw-page-title-main">Polonium dichloride</span> Chemical compound

Polonium dichloride is a chemical compound of the radioactive metalloid, polonium and chlorine. Its chemical formula is PoCl2. It is an ionic salt.

<span class="mw-page-title-main">Polonium hydride</span> Chemical compound

Polonium hydride (also known as polonium dihydride, hydrogen polonide, or polane) is a chemical compound with the formula PoH2. It is a liquid at room temperature, the second hydrogen chalcogenide with this property after water. It is very unstable chemically and tends to decompose into elemental polonium and hydrogen. It is a volatile and very labile compound, from which many polonides can be derived. Additionally, like all polonium compounds, it is highly radioactive.

The chalcogens react with each other to form interchalcogen compounds.

Polonium tetrachloride (also known as polonium(IV) chloride) is a chemical compound with the formula PoCl4. The salt is a hygroscopic bright yellow crystalline solid at room temperature. Above 200 °C, it tends to decompose into polonium dichloride and excess chlorine, similar to selenium tetrachloride and tellurium tetrachloride.

Polonium trioxide (also known as polonium(VI) oxide) is a chemical compound with the formula PoO3. It is one of three oxides of polonium, the other two being polonium monoxide (PoO) and polonium dioxide (PoO2). It is an interchalcogen that has so far only been detected in trace amounts.

Polonium monoxide (also known as polonium(II) oxide) is a chemical compound with the formula PoO. It is one of three oxides of polonium, the other two being polonium dioxide (PoO2) and polonium trioxide (PoO3). It is an interchalcogen.

Polonium dibromide (also known as polonium(II) bromide) is a chemical compound with the formula PoBr2. This salt is a purple-brown crystalline solid at room temperature. It sublimes (decomposing slightly) at 110 °C/30 μ and decomposes when melted in nitrogen gas at 270–280 °C.

<span class="mw-page-title-main">Post-transition metal</span> Category of metallic elements

The metallic elements in the periodic table located between the transition metals to their left and the chemically weak nonmetallic metalloids to their right have received many names in the literature, such as post-transition metals, poor metals, other metals, p-block metals and chemically weak metals. The most common name, post-transition metals, is generally used in this article.

Tellurium compounds are compounds containing the element tellurium (Te). Tellurium belongs to the chalcogen family of elements on the periodic table, which also includes oxygen, sulfur, selenium and polonium: Tellurium and selenium compounds are similar. Tellurium exhibits the oxidation states −2, +2, +4 and +6, with +4 being most common.

Polonium sulfide is an inorganic compound of polonium and sulfur with the chemical formula PoS. The compound is radioactive and forms black crystals.

Gallium compounds are compounds containing the element gallium. These compounds are found primarily in the +3 oxidation state. The +1 oxidation state is also found in some compounds, although it is less common than it is for gallium's heavier congeners indium and thallium. For example, the very stable GaCl2 contains both gallium(I) and gallium(III) and can be formulated as GaIGaIIICl4; in contrast, the monochloride is unstable above 0 °C, disproportionating into elemental gallium and gallium(III) chloride. Compounds containing Ga–Ga bonds are true gallium(II) compounds, such as GaS (which can be formulated as Ga24+(S2−)2) and the dioxan complex Ga2Cl4(C4H8O2)2. There are also compounds of gallium with negative oxidation states, ranging from -5 to -1, most of these compounds being magnesium gallides (MgxGay).

Americium compounds are compounds containing the element americium (Am). These compounds can form in the +2, +3, and +4, although the +3 oxidation state is the most common. The +5, +6 and +7 oxidation states have also been reported.

References

  1. 1 2 3 4 Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). CRC Press. p. 4.81. ISBN   978-1-4398-5511-9.
  2. 1 2 3 4 5 6 7 8 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. 594, ISBN   0-12-352651-5
  3. 1 2 3 Bagnall, K. W.; D'Eye, R. W. M. (1954). "The Preparation of Polonium Metal and Polonium Dioxide". J. Chem. Soc. RSC: 4295–4299. doi:10.1039/JR9540004295 . Retrieved 12 June 2012.
  4. 1 2 3 Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 780. ISBN   978-0-08-037941-8.
  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, ISBN   0-12-352651-5
  6. 1 2 3 4 5 6 Bagnall, K. W. (1962). "The Chemistry of Polonium". Advances in Inorganic Chemistry and Radiochemistry. New York: Academic Press. pp. 197–230. ISBN   978-0-12-023604-6 . Retrieved June 14, 2012.
  7. ↑ Ebbing, Darrell D.; Gammon, Steven D. (2009). General Chemistry (9 ed.). Boston: Houghton Mifflin Company. p. 320. ISBN   978-0-618-85748-7 . Retrieved June 14, 2012.
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