Silicon Halides

compounds of silicon and the halogens. Silicon halides of the following types are known (X = halogen): SiX₄, SiH_nX_4-n (halosilanes), Si_nX_2n+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 (SiH_nX_4-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 Si_nX_2n+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.