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In a Grain of Sand
| Article
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20585 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
11 / 1992 |
2,976 Words |
| Author
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Harold Goldwhite
Harold Goldwhite is professor of chemistry at California
State University, Los Angeles. |
The beaches of the Caribbean are known for their beautiful white sands; that sand is the dioxide of the element silicon. After oxygen, silicon is the second most abundant element in the solid crust of the earth. It is present not only in silica sands, but also in an astonishing variety of compounds containing, besides oxygen, a range of metals. Collectively called silicates, these materials are the major constituents of the earth's crust. Silicon compounds are, literally, as common as dirt. Some less common silicates are highly prized for their color and the beauty of their crystals, such as the gemstones beryl, garnet, jade, opal, topaz, and zircon.
Silicon bonds readily and tenaciously with oxygen so that all naturally occurring silicon compounds contain oxygen. The free element was not prepared until early in the nineteenth century, and then only in an impure form. In the mid and late-twentieth century there were major innovations in the chemistry and applications of silicon and its compounds that have turned them into indispensable materials for modern technology.
Silicon appears below carbon in Group 4 of the periodic table of elements. While there are some superficial similarities between silicon and carbon, both, for example, have a valency of found, which means they form compounds in which four other atoms or groups are bound to the silicon or carbon, there also are major differences between the two. In particular while carbon readily forms double and triple bonds with other atoms, including other carbon atoms, it is only recently that silicon has been shown to form double bonds, and then only in a few special compounds.
Arrowheads And Building Blocks
The name silicon derives from the Latin word silex, meaning flint, which is impure silicon dioxide, or silica, in a glassy, noncrystalline form. Our Stone Age ancestors discovered that flint pebbles, when struck against each other, resulted in flakes with sharp cutting edges. These flakes made excellent flint tools, such as knives and arrow-and spearheads.
Other advances using silicon compounds came about in time. Clays, which are found in many soils, are silicates that contain aluminum. When mixed with water they form a pliable mass that can be molded and cast as desired. When the clay-water mixture is heated, the water evaporates and structural changes occur in the silicates, making them rigid and strong, though relatively brittle, materials. Bricks, tiles, and
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