Si

Si, river, China: see Xi.

Si, symbol for the element silicon.

SI: see International System of Units.

Nonmetallic to semimetallic chemical element, chemical symbol Si, atomic number 14. Second only to oxygen in abundance in Earth's crust, it never occurs free but is found in almost all rocks and in sand, clay, and soils, combined with oxygen as silica (silicon dioxide, SiO₂) or with oxygen and metals as silicate minerals. It occurs in many plants and some animals. Pure silicon is a hard, dark gray solid with a metallic lustre and the same crystal structure as diamond. It is an extremely important semiconductor; doped (see dopant) with boron, phosphorus, or arsenic, it is used in various electronic circuit and switching devices, including computer chips, transistors, and diodes. Silicon is also used in metallurgy as a reducing (see reduction) agent and in steel, brass, and bronze. Its usual valence in compounds is 4. Silica is used in the form of sand and clay for many purposes; as quartz, it may be heated to form special glasses. Silicates are used in making glass, enamels, and ceramics; sodium silicates (water glass) are used in soaps, wood treatment, cements, and dyeing. Seealso silane; silicone.

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Industrial region, west-central California. Roughly bounded by San Francisco Bay on the north, the Santa Cruz Mountains on the west, and the Diablo Range on the east, it takes its (unofficial) name from the extensive use of silicon in the region's electronics industries. The U.S. government invested heavily in the region's industry following World War II. A second economic surge occurred with the proliferation of personal computers in the 1980s, and a third surge followed the growth of the Internet in the 1990s.

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In Inuit mythology, Ka-Ha-Si was a lazy Inuit boy who was shunned by his tribe for his constant sleeping. In a dream, a loon spoke to him and said he had to save his tribe from a famine because the hunters had been unable to find game. Ka-Ha-Si tricked a group of walruses into killing each other, but his fame for saving the tribe quickly evaporated. And he was once again teased for his laziness. The same dream recurred and Ka-Ha-Si fought a giant the next day, who had been beating all the men of his tribe in wrestling matches. Ka-Ha-Si ended up becoming a wise and well-respected shaman.