Silicon and germanium

Silicon is a hard, dark-gray nonmetallic ele­ment. It is very abundant, making up about 28 per cent of the earth's crust. Only oxygen is more plentiful. Silicon occurs exclusively in compounds, combined chiefly with oxygen in many types of silicates. There are more than 800 known natural silicates.

Silica, a type of silicate, is the main ingredi­ent of sand. It is also a major ingredient of quartz, lava, and various minerals that form rocks such as granite and sandstone. A new form of silica was produced when the first atomic bomb was exploded in New Mexico.

Pure silicon is indispensable to the elec­tronics industry because it is a good semicon­ductor. A semiconductor conducts electricity with an efficiency between that of conductors (like metal) and insulators (like glass). This al­lows for greater control in transmitting elec­tric signals. Thus, pure silicon is used in mak­ing integrated circuits, solar cells, transistors, and similar devices that transmit electric sig-

nals. In 1950, 2 ounces (56 grams) of extremely pure silicon produced 50 transistors. In 1980, the same amount provided one million transis­tors, as integrated circuits. A single integrated circuit can now hold more than 10,000 transis­tors and still efficiently and accurately control electric signals.

Silicon compounds are also widely used in industry—in making glass, in grinding and pol­ishing other materials, in producing synthetic rubber, and in making lubricants, insulators, and water repellents.

Germanium is a hard, brittle, grayish-whitfe metal. It is comparatively rare, being found in small amounts in copper, lead, and zinc ores. Germanium, like silicon, is widely used as a semiconductor, especially in diodes and solar batteries. It is also used in certain kinds of tele­phone lines, data transmission lines, and com­puter cables, as well as in some lead-acid stor­age batteries, and in medicine.

Tin

Tin is a malleable white metal that is found pri­marily in the southern hemisphere. It makes up only about .001 per cent of the earth's crust. Malaysia is the world's leading producer of tin.

Tin was one of the earliest metals known and its use has closely followed the growth of civilization. Food canning and preservation de­veloped with tin-coated steel. Fast machinery depended on tin-based bearings. Printing ex­panded with metal type that contained tin. Many communications devices first depended on tin-based solder (an alloy used to join metal surfaces). Tin alloys are used for musical in­struments and, especially, organ pipes. Be­cause the metal is comparatively rare in na­ture, it is now sufficiently expensive for tin cans to be collected and the tin extracted and recycled.

Tin can be easily formed into complex shapes. It also protects steel from rusting. For these and other reasons, tin is chiefly used today to make tin plate. Tin plate is a very thin film of tin used to coat both sides of a piece of steel. Tin-plated steel is used chiefly for mak­ing tin cans. Tin coatings are also applied to staples, pins, paper clips, and containers and utensils for handling and storing food.

Tin is a major ingredient of solder (tin and lead), bronze (tin and copper), and pewter (tin, antimony, and copper). Small amounts of tin also go into the making of bearings, dental fill­ings, toothpastes, printing alloys, and cast iron.

Lead

Lead is a soft but heavy bluish-gray metal. It is widely distributed in the earth's crust, usually found in a gray metallic ore called galena. Ga­lena most often contains other metals also, such as copper, gold, silver, and zinc. The world's leading lead-mining countries are Aus­tralia and the Soviet Union.

Lead is very soft and malleable. It is easily cast, joined, and converted into pipes or sheets. The principal modern use of the metal is in the electrodes of storage batteries. These batteries provide power for the electrical sys­tems of automobiles, airplanes, and many other vehicles. Lend is also added to gasoline

Major groups of elements: Silicon to lead 39

The eroded sandstone pinnaclesof Bryce Canyon in the United States (left) and the stained glass win­dow(below) both consist largely of silica. In the sand­stone, the silica is in the form of quartz. In the stained glass, it is mixed with lead oxide. Most old stained glass also contains various metal compounds to make it colored. Gold, for instance, produces red glass.

Fact entries

Siliconwas first isolated in 1823 by the Swedish chem­ist Jons Berzelius (1779-1848). Its name is derived from the Latin si/ex, mean­ing flint. At. no. 14; at. mass 28.0855; m.p. 1410° C; b.p. 2355' C.

Germaniumwas predicted in 1871 by the Russian chemist Dmitri Mendeleev (1834-1907). It was not dis­covered until 1886 by the German chemist Clemens Winkler (1838-1894). He named it after his homeland.

At. no. 32; at. mass 72.59; m.p. 937.4° C; b.p. about 2830° C.

Tin,in the form of bronze (an alloy with copper), has been known since at least 3500 B.C. Its chemical sym-

bol, Sn, comes from the Latin word for the element, stannum. One naturally oc­curring form of tin—gray tin—is powdery at low tem­peratures. At. no. 50; at. mass 118.71; m.p. 231.9° C; b.p. 2270° C.

Leadhas been known as a metal since at least 4000 B.C. Its chemical symbol, Pb, is derived from the Latin word for the element, plumbum. At. no. 82; at. mass 207.19; m.p. 327.5° C; b.p. 1740° C.

Date: 2015-12-11; view: 1300