Silicon compounds are compounds containing the element silicon (Si). As a carbon group element, silicon often forms compounds in the +4 oxidation state, though many unusual compounds have been discovered that differ from expectations based on its valence electrons, including the silicides and some silanes. Metal silicides, silicon halides, and similar inorganic compounds can be prepared by directly reacting elemental silicon or silicon dioxide with stable metals or with halogens. Silanes, compounds of silicon and hydrogen, are often used as strong reducing agents, and can be prepared from aluminum–silicon alloys and hydrochloric acid.
Several inorganic compounds have been formed with silicon and other nonmetals such as sulfur and nitrogen; most of these compounds are highly incompatible with water. One of the most useful and successfully marketed inorganic silicon compounds is silicon carbide.
Naturally occurring silicon is found in silicate and aluminosilicate minerals. One of the most common silicon compounds found in the Earth's crust is silicon dioxide or silica, which often occurs as quartz.
Organosilicon compounds are fairly stable due to the similarity in strength of the Si–C bond to the C–C bond. Organosilicates include silicone polymers.