Editing Metalloid (section)

===Polonium===
{{Main|Polonium}}
Polonium is "distinctly metallic" in some ways.<ref name="Cotton FA 1999, p.502">[[#Cotton1999|Cotton et al. 1999, p.&nbsp;502]]</ref> Both of its allotropic forms are metallic conductors.<ref name="Cotton FA 1999, p.502"/> It is soluble in acids, forming the rose-coloured Po<sup>2+</sup> cation and displacing hydrogen: Po + 2 H<sup>+</sup> → Po<sup>2+</sup> + H<sub>2</sub>.<ref>[[#Wiberg2001|Wiberg 2001, p.&nbsp;594]]</ref> Many polonium salts are known.<ref>[[#Greenwood2002|Greenwood & Earnshaw 2002, p.&nbsp;786]]; [[#Schwietzer2010|Schwietzer & Pesterfield 2010, pp.&nbsp;242–43]]</ref> The oxide [[polonium dioxide|PoO<sub>2</sub>]] is predominantly basic in nature.<ref name=Bagnall1966p41>[[#Bagnall1966|Bagnall 1966, p.&nbsp;41]]; [[#Nickless1968|Nickless 1968, p.&nbsp;79]]</ref> Polonium is a reluctant oxidizing agent, unlike its lightest congener oxygen: highly [[reducing agent|reducing conditions]] are required for the formation of the Po<sup>2−</sup> anion in aqueous solution.<ref>[[#Bagnall1990|Bagnall 1990, pp.&nbsp;313–14]]; [[#Lehto2011|Lehto & Hou 2011, p.&nbsp;220]]; [[#Siekierski2002|Siekierski & Burgess 2002, p.&nbsp;117]]: "The tendency to form X<sup>2−</sup> anions decreases down the Group [16 elements]&nbsp;..."</ref>

Whether polonium is ductile or brittle is unclear. It is predicted to be ductile based on its calculated [[Young's modulus#Relation among elastic constants|elastic constants]].<ref>[[#Legit|Legit, Friák & Šob 2010, pp.&nbsp;214118–18]]</ref> It has a simple [[cubic crystal system|cubic crystalline structure]]. Such a structure has few [[Slip (materials science)#slip systems|slip systems]] and "leads to very low ductility and hence low fracture resistance".<ref>[[#Halford|Manson & Halford 2006, pp.&nbsp;378, 410]]</ref>

Polonium shows nonmetallic character in its halides, and by the existence of [[polonide]]s. The halides have properties generally characteristic of nonmetal halides (being volatile, easily hydrolyzed, and soluble in [[organic solvent]]s).<ref>[[#Bagnall1957|Bagnall 1957, p.&nbsp;62]]; [[#Fernelius1982|Fernelius 1982, p.&nbsp;741]]</ref> Many metal polonides, obtained by heating the elements together at 500–1,000&nbsp;°C, and containing the Po<sup>2−</sup> anion, are also known.<ref>[[#Bagnall1966|Bagnall 1966, p.&nbsp;41]]; [[#Barrett2003|Barrett 2003, p.&nbsp;119]]</ref>