with a hardness similar to lead. It has a simple cubic crystalline structure characterised (as determined by electron density calculations) by partially directional bonding, and a BCN of 6. Such a structure ordinarily results in very low ductility and fracture resistance however polonium has been predicted to be a ductile metal. It forms a covalent hydride; its halides are covalent, volatile compounds, resembling those of tellurium. The oxide of polonium in its preferred oxidation state (PoO2; +4) is predominantly basic, but amphoteric if dissolved in concentrated aqueous alkali, or fused with potassium hydroxide in air. The yellow polonate(IV) ion is known in aqueous solutions of low Cl‒ concentration and high pH. Polonides such as Na2Po, BePo, ZnPo, CdPo and HgPo feature Po2− anions; except for HgPo these are some of the more stable of the polonium compounds. Livermorium is expected to be less reactive than moscovium. The standard reduction potential of the Lv2+/Lv couple is expected to be around +0.1 V. It should be most stable in the +2 oxidation state; the 7p3/2 electrons are expected to be so weakly bound that the first two ionisation potentials of livermorium should lie between those of the reactive alkaline earth metals magnesium and calcium. The +4 oxidation state should only be reachable with the most electronegative ligands. Livermorium(II) oxide (LvO) should be basic and livermorium(IV) oxide (LvO2) should be amphoteric, analogous to polonium. Group 17 Astatine is a radioactive element that has never been seen; a visible quantity would immediately be vaporised due to its intense radioactivity. It may be possible to prevent this with sufficient cooling. Astatine is commonly regarded as a nonmetal, less commonly as a metalloid and occasionally as a metal. Unlike its lighter congener iodine, evidence for diatomic astatine is sparse and inconclusive. In 2013, on the basis of relativistic modelling, astatine was predicted to be a monatomic metal, with a face-centered cubic crystalline structure. As such, astatine could be expected to have a metallic appearance; show metallic conductivity; and have excellent ductility, even at cryogenic temperatures. It could also be expected to show significant nonmetallic character, as is normally the case for metals in, or in the vicinity of, the p-block. Astatine oxyanions AtO−, and are known, oxyanion formation being a tendency of nonmetals. The hydroxide of astatine At(OH) is presumed to be amphoteric. Astatine forms covalent compounds with nonmetals, including hydrogen astatide HAt and carbon tetraastatide