gold (redirected from atomic number 79)

gold, metallic chemical element; symbol Au [Lat. aurum=shining dawn]; at. no. 79; at. wt. 196.9665; m.p. 1,064.43°C;; b.p. 2,808°C;; sp. gr. 19.32 at 20°C;; valence +1 or +3.

Gold is very ductile and is the most malleable metal; it can be beaten into extremely thin sheets of gold leaf. Only silver and copper, which are above it in Group 11 of the periodic table, are better electrical conductors. Gold is chemically inactive. It is unaffected by moisture, oxygen, or ordinary acids but is attacked by the halogens. Aqua regia (a mixture of nitric and hydrochloric acids that liberates chlorine) is so named for its ability to dissolve gold, the "king" of the metals. Gold forms both aurous (univalent) and auric (trivalent) compounds; auric chloride and chloroauric acid are its most common compounds.

A relatively soft metal, gold is usually hardened by alloying with copper, silver, or other metals. White gold, a substitute for platinum, is an alloy of gold with platinum, palladium, nickel, or nickel and zinc. Green gold, also used by jewelers, is usually an alloy of gold with silver. Alloys of gold with copper are a reddish yellow and are used for coinage and jewelry. Gold is often found in nature alloyed with other metals; when more than 20% of silver is present the alloy is called electrum. The gold content of an alloy is commonly stated in carats, a carat being 1-24 part by weight of the total mass. Pure gold is therefore 24 carats fine; an alloy that is 75% gold is 18 carats fine. Fineness is sometimes expressed in terms of parts per thousand; thus gold containing 10% of other metals is said to have a fineness of 900.

Gold is widely distributed on the earth; although large amounts are present also in seawater, the cost of current methods for recovering it exceeds its value. Most gold is found in the metallic state in the form of dust, grains, flakes, or nuggets. It occurs, usually in association with silver or other metals, in quartz veins or lodes so finely disseminated that it is not visible. It is found also in alluvial placer deposits, which are worked by panning, dredging, and hydraulic mining. Gold is extracted from its ores by mechanical means and separated from other metals by chemical processes, notably the cyanide process, the amalgamation process, and the chlorination process (in this the ore is oxidized and chlorinated and the gold precipitated with hydrogen sulfide). It also occurs in compounds, notably telluride minerals.

Gold has been known from prehistoric times and was possibly the first metal used by humans. It was valued for ornaments (see goldwork

The Ancient World

The earliest-known fine goldwork is from Ur in Mesopotamia. Dating from c.
..... ), and magical efficacy was attributed to it. In the Middle Ages alchemists sought to transmute baser metals into gold. The quest for gold stimulated European explorations and conquests in the Western Hemisphere, and its discovery has led to many a gold rush. Much of the gold now extracted is used for jewelry. The chief producers are South Africa, the United States (especially in Nevada and Alaska), Australia, Canada, Russia, China, Brazil, Uzbekistan, Papua New Guinea, and Indonesia. For a discussion of the monetary function of gold, see bimetallism; coin; international monetary system; money.

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gold

Metallic chemical element, one of the transition elements, chemical symbol Au, atomic number 79. It is a dense, lustrous, yellow, malleable precious metal, so durable that it is virtually indestructible, often found uncombined in nature. Jewelry and other decorative objects have been crafted from gold for thousands of years. It has been used for coins, to back paper currencies, and as a reserve asset. Gold is widely distributed in all igneous rocks, usually pure but in low concentrations; its recovery from ores and deposits has been a major preoccupation since ancient times (see cyanide process). The world's gold supply has seen three great leaps, with Christopher Columbus's arrival in the Americas in 1492, with discoveries in California (see gold rush) and Australia (1850–75), and discoveries in Alaska, Yukon (see Klondike), and South Africa (1890–1915). Pure gold is too soft for prolonged handling; it is usually used in alloys with silver, copper, and other metals. In addition to being used in jewelry and as currency, gold is used in electrical contacts and circuits, as a reflective layer in space applications and on building windows, and in filling and replacing teeth. Dental alloys are about 75% gold, 10% silver. In jewelry, its purity is expressed in 24ths, or karats: 24-karat is pure, 12-karat is 50% gold, etc. Its compounds, in which it has valence 1 or 3, are used mainly in plating and other decorative processes; a soluble chloride compound has been used to treat rheumatoid arthritis.

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gold

color of the sun’s rays. [Color Symbolism: Jobes, 357]

See : Sun

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gold

symbol of sagacity. [Color Symbolism: Jobes, 356]

See : Wisdom