Silicon °C respectively are the second-highest among all the metalloids and nonmetals, being only surpassed by boron. Silicon is the eighth most common element in the universe by mass, but very rarely occurs as the pure element in the Earth's crust. It is most widely distributed in dusts, sands, planetoids, and planets as various forms of silicon dioxide (silica) or silicates. More than 90% of the Earth's crust is composed of silicate minerals, making silicon the second most abundant element in the Earth's crust (about 28% by mass) after oxygen. Most silicon is used commercially without being separated, and often with
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