Antimony discontinued. Antimony is resistant to attack by acids. Four allotropes of antimony are known: a stable metallic form and three metastable forms (explosive, black and yellow). Elemental antimony is a brittle, silver-white shiny metalloid. When slowly cooled, molten antimony crystallizes in a trigonal cell, isomorphic with the gray allotrope of arsenic. A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride. When scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms; when rubbed with a pestle in a mortar, a strong detonation occurs. Black antimony
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