compounds of silicon and the halogens. Silicon halides of the following types are known (X = halogen): SiX4, SiHnX4-n (halosilanes), SinX2n+2, and mixed halides, such as SiC1Br3.
Under normal conditions, SiF4 is a gas, SiC14 and SiBr4 are liquids (melting points, —68.8° and 5°C), and SiI4 is a solid (melting point, 124° C). The SiX4 compounds are readily hydro-lyzed: SiX4 + 2H2O = SiO2 + 4HX. They fume in air owing to the formation of very fine particles of SiO2; silicon tetrafluo-ride reacts differently: 3SiF4 +2H2O = SiO2 + 2H2SiF6.
Chlorosilanes (SiHnX4-n), such as SiHCI3 (prepared by the reaction of gaseous HC1 with Si), react with water to give polymeric compounds with a strong siloxane chain Si—O—Si. Chlorosilanes, being highly reactive, are the starting materials used in the synthesis of organosilicon compounds.
Compounds of the type SinX2n+2, which contain chains of Si atoms, give a series of compounds when X is chlorine, which includes Si6Cl14 (melting point, 320°C). The remaining halogens form Si2X6 only.
Compounds of the types (SiX2)n and (SiX)n have also been obtained. Molecules of SiX2 and SiX exist at high temperatures in gaseous form and on rapid cooling (with liquid nitrogen) form solid polymeric materials, which are insoluble in the usual organic solvents.
Silicon Tetrachloride, SiCI4, is used in the production of lubricants, electrical insulating materials, coolants, hydrophobizing liquids, and other products.
V. P. BARZAKOVSKII