Silicon - Silicones
Like silicates, silicones are a family of compounds held together by strong Si-O-Si bridges. But where silicates have two additional, non-bridging oxygen atoms attached to each silicon atom, the silicones have organic groups-for example, two methyl groups, CH3. The resulting (CH3)2SiO-groups can build up into long chains, just as the silicates. In contrast, however, are organic groups in the chains, that allow the compounds to resemble organic materials such as oils, greases, and rubbers.
As with organic compounds, a variety of silicone compounds can be composed of various-length silicon-oxygen chains with organic groups attached. The smaller molecules are the basis of silicone oils that, as with the all-organic petroleum oils, are used as lubricants but which better resist decomposition at higher temperatures. Very large silicone molecules make silicone rubbers with high compression elasticity. These compounds are incorporated into ranging from super-bouncing balls to high impact bumpers. The first human footprint on the moon was made with a silicone-rubber-soled boot.
Between the oils and rubbers are hundreds of kinds of silicones that are used in electrical insulators, rust preventives, soaps, fabric softeners, hair sprays, hand creams, furniture and auto polishes, paints, adhesives, and chewing gum. Silicones are also used in surgical implants because they less prone that organic material to rejection by the immune system.