compounds of silicon and hydrogen. Only saturated silicon hydrides (silanes) of the general formula SinH2n+2 have been isolated; silanes up to octasilane, Si8H18, have been obtained. At room temperature, the first two silicon hydrides—monosilane, SiH4, and disilane, Si2H6 —are gaseous, and the rest are volatile liquids. All silicon hydrides have an unpleasant odor and are toxic. They are far less stable than alkanes and are pyrophoric on exposure to air; for example, 2Si2H6 + 7O2 = 4SiO2 + 6H2O. Silicon hydrides dissociate in water: Si3H8 + 6H2O = 3SiO2 + 10H2.
No silicon hydrides occur freely in nature. Under laboratory conditions, the interaction of diluted acids and magnesium silicide produces a mixture of various silicon hydrides, which is subjected to strong cooling and then separated by fractional distillation in the full absence of air.