Nonmetal are called "metalloids" mainly in light of their physical resemblance to metals. While they each have a metallic appearance, they are brittle and only fair conductors of electricity. Boron, silicon, germanium, tellurium are semiconductors. Arsenic and antimony have the electronic band structures of semimetals although both have less stable semiconducting allotropes. Astatine has been predicted to have a metallic crystalline structure. Chemically the metalloids generally behave like (weak) nonmetals. They have moderate ionisation energies, low to high electron affinities, moderate electronegativity values, are poor to moderately strong oxidising agents, and demonstrate a tendency to form alloys with metals. The reactive
Arsenic pentachloride Arsenic pentachloride Arsenic pentachloride is a chemical compound of arsenic and chlorine. This compound was first prepared in 1976 through the UV irradiation of arsenic trichloride, AsCl, in liquid chlorine at −105 °C. AsCl decomposes at around −50 °C. The structure of the solid was finally determined in 2001. AsCl is similar to phosphorus pentachloride, PCl in having a trigonal bipyramidal structure where the equatorial bonds are shorter than the axial bonds (As-Cl = 210.6 pm, 211.9 pm; As-Cl= 220.7 pm). The pentachlorides of the elements above and below arsenic in group 15, phosphorus pentachloride and antimony pentachloride are much