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Polonium dioxide
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<h2 id="structure-and-appearance">Structure and appearance</h2> <p>At room temperature, polonium dioxide has a <a href="/facts/Face-centered_cubic/92Co7BKM">face-centered cubic</a> (<a href="/facts/Fluorite/y2G7C8zk">fluorite</a>) crystal structure; upon heating to high temperatures, it crystallises in the <a href="/facts/Tetragonal_crystal_system/12Aop255">tetragonal crystal system</a>. 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.<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a><a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a> The <a href="/facts/Ionic_radius/C3dwKrrB">ionic radius</a> of the Po4+ <a href="/facts/Ion/3bePpDna">ion</a> is 1.02 or 1.04 <a href="/facts/Angstrom/T5mjdd97">Å</a>; 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.<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a> </p> <h2 id="occurrence">Occurrence</h2> <p>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.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a> </p> <h2 id="preparation">Preparation</h2> <p>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 <a href="/facts/Polonium_disulfate/cBNA6gMx">polonium disulfate</a> (Po(SO4)2), polonium selenate (Po(SeO4)2), or <a href="/facts/Polonium_tetranitrate/R5XHV0jo">polonium tetranitrate</a> (Po(NO3)4).<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a><a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> </p> <h2 id="chemistry">Chemistry</h2> <p>When placed in <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a>, polonium dioxide is slowly <a href="/facts/Redox/Pyd5RVcj">reduced</a> to metallic polonium at 200 °C; the same reduction occurs at 250 °C in <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> or <a href="/facts/Hydrogen_sulfide/UbCqjMMk">hydrogen sulfide</a>. When heated in <a href="/facts/Sulfur_dioxide/jDK1fIDs">sulfur dioxide</a> at 250 °C, a white compound is formed, possibly a polonium <a href="/facts/Sulfite/xdppUlKA">sulfite</a>.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> When polonium dioxide is hydrated, polonous acid (H2PoO3), a pale yellow, voluminous <a href="/facts/Precipitate/s3BgsLLY">precipitate</a>, is formed. Despite its name, polonous acid is an <a href="/facts/Amphoteric/2UrXEsyl">amphoteric</a> compound, reacting with both <a href="/facts/Acid/FySU18n1">acids</a> and <a href="/facts/Base_(chemistry)/M9wA7qeM">bases</a>.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a><a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> </p><p><a href="/facts/Halogenation/vYrGVWcJ">Halogenation</a> of polonium dioxide with the <a href="/facts/Hydrogen_halide/avUQ6Nwy">hydrogen halides</a> yields the polonium tetra<a href="/facts/Halide/ujYu8kGD">halides</a>:<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p> PoO2 + 4 <a href="/facts/Hydrogen_fluoride/XfQxlqR6">HF</a> → PoF4 + 2 <a href="/facts/Water/0lkXnJPK">H2O</a> PoO2 + 4 <a href="/facts/Hydrogen_chloride/7Wzkhomd">HCl</a> → <a href="/facts/Polonium_tetrachloride/e6pD101s">PoCl4</a> + 2 H2O PoO2 + 4 <a href="/facts/Hydrogen_bromide/rUw1duLA">HBr</a> → <a href="/facts/Polonium_tetrabromide/0eMnCgIE">PoBr4</a> + 2 H2O PoO2 + 4 <a href="/facts/Hydrogen_iodide/tlfNemUK">HI</a> → <a href="/facts/Polonium_tetraiodide/WSR6k6EJ">PoI4</a> + 2 H2O <p>In reactions, polonium dioxide behaves very much like its homologue <a href="/facts/Tellurium_dioxide/yrILUsAM">tellurium dioxide</a>, forming Po(IV) salts; however, the acidic character of the <a href="/facts/Chalcogen/nXLGmnqL">chalcogen</a> oxides decreases going down the group, and polonium dioxide and polonium(IV) hydroxide are much less acidic than their lighter homologues.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> For example, <a href="/facts/Sulfur_dioxide/jDK1fIDs">SO2</a>, <a href="/facts/Sulfur_trioxide/Ijvm08Lq">SO3</a>, <a href="/facts/Selenium_dioxide/naIqT939">SeO2</a>, <a href="/facts/Selenium_trioxide/X6Fm1XTl">SeO3</a> and <a href="/facts/Tellurium_trioxide/P0C2fSd5">TeO3</a> are acidic, but <a href="/facts/Tellurium_dioxide/yrILUsAM">TeO2</a> is amphoteric, and PoO2, while amphoteric, even shows some <a href="/facts/Base_(chemistry)/M9wA7qeM">basic</a> character.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p><p>The reaction of polonium dioxide with <a href="/facts/Potassium_hydroxide/NBhPBuXc">potassium hydroxide</a> or <a href="/facts/Potassium_nitrate/TycqMdcG">potassium nitrate</a> in air gives the colourless potassium polonite (K2PoO3):<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> PoO2 + 2 KOH → K2PoO3 + H2O PoO2 + 2 KNO3 → K2PoO3 + 2 <a href="/facts/Nitric_oxide/UvhdvDzp">NO</a> <p>Polonium dioxide is closely related to the polonite anion (PoO2−3), similar to the relationship between <a href="/facts/Polonium_trioxide/sKUqRsej">polonium trioxide</a> and the polonate anion (PoO2−4). </p> <h2 id="applications">Applications</h2> <p>Polonium dioxide has no uses outside of basic research.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p> <h2 id="precautions">Precautions</h2> <p>Polonium, whether in elemental form or as any polonium compound, such as polonium dioxide, is extremely <a href="/facts/Radioactive/Ya6FVjt4">radioactive</a>. Thus PoO2 must be handled in a <a href="/facts/Glove_box/NnR37n6E">glove box</a>. 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 <a href="/facts/Rubber/CbsjJxhY">rubber</a> do not provide sufficient protection against the radiation from polonium; surgical gloves are necessary. <a href="/facts/Neoprene/MtLEdFvE">Neoprene</a> gloves shield radiation from polonium better than natural rubber.<a class="footnote-ref" id="fnref:16" href="#fn:16"><sup>16</sup></a> </p> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>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 <a href="0-12-352651-5" target="_blank">0-12-352651-5</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>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 <a href="0-12-352651-5" target="_blank">0-12-352651-5</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>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. <a href="http://pubs.rsc.org/en/content/articlelanding/1954/jr/jr9540004295" target="_blank">http://pubs.rsc.org/en/content/articlelanding/1954/jr/jr9540004295</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>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. <a href="978-0-12-023604-6" target="_blank">978-0-12-023604-6</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>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 <a href="0-12-352651-5" target="_blank">0-12-352651-5</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>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 <a href="0-12-352651-5" target="_blank">0-12-352651-5</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 780. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>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. <a href="978-0-12-023604-6" target="_blank">978-0-12-023604-6</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>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 <a href="0-12-352651-5" target="_blank">0-12-352651-5</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 780. ISBN 978-0-08-037941-8. <a href="978-0-08-037941-8" target="_blank">978-0-08-037941-8</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>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 <a href="0-12-352651-5" target="_blank">0-12-352651-5</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>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. <a href="978-0-12-023604-6" target="_blank">978-0-12-023604-6</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> <li id="fn:13"><p>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. <a href="978-0-618-85748-7" target="_blank">978-0-618-85748-7</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></p></li> <li id="fn:14"><p>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. <a href="978-0-12-023604-6" target="_blank">978-0-12-023604-6</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></p></li> <li id="fn:15"><p>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. <a href="978-0-12-023604-6" target="_blank">978-0-12-023604-6</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></p></li> <li id="fn:16"><p>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. <a href="978-0-12-023604-6" target="_blank">978-0-12-023604-6</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></p></li> </ol>