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2,491 results for: gold
| Dictionary.com Unabridged (v 1.1) | Cite This Source |
Audio Help [gohld] Pronunciation Key | 1. | Herbert, born 1924, U.S. novelist and short-story writer. |
| 2. | Thomas, 1920–2004, U.S. astronomer, born in Austria: formulated the steady-state theory of the universe. |
| Dictionary.com Unabridged (v 1.1) Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006. |
| Dictionary.com Unabridged (v 1.1) | Cite This Source |
| Dictionary.com Unabridged (v 1.1) Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006. |
| Dictionary.com Unabridged (v 1.1) | Cite This Source |
Audio Help [gohld] Pronunciation Key | 1. | a precious yellow metallic element, highly malleable and ductile, and not subject to oxidation or corrosion. Symbol: Au; atomic weight: 196.967; atomic number: 79; specific gravity: 19.3 at 20°C. |
| 2. | a quantity of gold coins: to pay in gold. |
| 3. | a monetary standard based on this metal; gold standard. |
| 4. | money; wealth; riches. |
| 5. | something likened to this metal in brightness, preciousness, superiority, etc.: a heart of gold. |
| 6. | a bright, metallic yellow color, sometimes tending toward brown. |
| 7. | gold medal. |
| 8. | (initial capital letter) Military. the code name for one of the five D-day invasion beaches, assaulted by British troops. |
| 9. | consisting of gold. |
| 10. | pertaining to gold. |
| 11. | like gold. |
| 12. | of the color of gold. |
| 13. | indicating the fiftieth event of a series, as a wedding anniversary. |
| 14. | (of a record, CD, or cassette) having sold a minimum of 500,000 copies. |
] | Dictionary.com Unabridged (v 1.1) Based on the Random House Unabridged Dictionary, © Random House, Inc. 2006. |
| Synonym Collection v1.1 | Cite This Source | |
| Main Entry: | gold | |
| Part of Speech: | adjective | |
| Synonyms: | aureate, gilded, halcyon, aurelian, auric, auriferous, aurous, gilt | |
| Source: | Synonym Collection v1.1 Copyright © 2008 by Lexico Publishing Group, LLC. | |
| Synonym Collection v1.1 | Cite This Source | |
| Main Entry: | gold | |
| Part of Speech: | noun | |
| Synonyms: | (uncoined gold). associated words:alchemist, alchemy, alloy, assay, aureate, billet, bonanza, foil, gild, gilded, ingot, lode, nugget, ore, pinchbeck, amalgamated, assayer, assaying, aurated, auric, auriferous, aurific, aurigraphy, aurivorous, aurocephalous, aurous, aurum, blick, bullion, carat, chlorination, chrysography, cupel, cupellation, filigree, gilding, gilt, goldsmith, inaurate, inauration, lingot, mannheim gold, noble metal, ormolu, orphrey, orris, platinum, schlich, vermeil | |
| Source: | Synonym Collection v1.1 Copyright © 2008 by Lexico Publishing Group, LLC. | |
| Synonym Collection v1.1 | Cite This Source | |
| Main Entry: | gold | |
| Part of Speech: | verb | |
| Synonyms: | pan, prospect, fossick | |
| Source: | Synonym Collection v1.1 Copyright © 2008 by Lexico Publishing Group, LLC. | |
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| Columbia Electronic Encyclopedia | Cite This Source |
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), 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.
The Columbia Electronic Encyclopedia Copyright © 2004, Columbia University Press.
Licensed from Columbia University Press
| Chemical Elements: From Carbon to Krypton | Cite This Source |
Overview
Gold has been called the most beautiful of all chemical elements. Its beauty has made it desirable for use in jewelry, coins, and artwork for thousands of years. It was one of the first pure metals to be used by humans.
Gold is one of the few elements that can affect politics and economics. Wars have been fought over access to gold. Cities and towns have sprung up and died out as gold was discovered and then mined out. Many nations still count their wealth according to the amount of gold they keep in storage.
Gold lies in the middle of the periodic table. The periodic table is a chart that shows how elements are related to one another. Gold is a heavy metal in a group known as the transition metals. Gold is also known as a precious metal (as are platinum and silver).
Large amounts of gold are still used in the manufacture of coins, medals, jewelry, and art. Gold also has a number of uses in industry, medicine, and other applications. For example, one radioactive isotope of gold is commonly used to treat cancer.
The chemical symbol for gold is Au. The symbol comes from the Latin word for gold, aurum. Aurum means "shining dawn."
Discovery and naming
Gold objects dating to 2600 B.C. have been found. They were discovered in the royal tombs of the ancient civilization of Ur. These objects showed that humans had already learned how to work with gold this early in history. Some of the gold, for example, had been formed into wires.
One of the special skills developed by the Egyptians was the adding of gold to glass objects. They found a way to use gold to make glass a beautiful ruby-red color. The glass became known as gold ruby glass.
Gold is also mentioned in a number of places in the Bible. A passage in Exodus, for example, refers to the clothing worn by Aaron: "And they did beat the gold into thin plates, and cut it into wires, to work it in the blue, and in the purple, and in the scarlet, and in the fine linen, with cunning work."
Writings from every stage of human history tell of the discovery and use of gold. Roman historian Pliny the Elder (A.D. 23-79), for example, describes gold-mining locations. The Romans found it lying in stream beds in the Tagus River in Spain, the Po River in Italy, the Hebrus River in Thracia (now Greece), the Pactolus River in Asia Minor (now Turkey), and the Ganges River in India.
Gold has long been known in the New World, too. During a visit to Haiti, Christopher Columbus (1451-1506) found gold nuggets lying on the bottom of rivers and harbors. A Portuguese explorer in 1586, Lopez Vaz, wrote that the region called Veragua (now Panama) was the "richest Land of Gold [in] all the rest of the Indies."
In the United States, of course, the most famous story about gold occurred in the late 1840s. Thousands of people flocked to California in search of gold. This era was called the Gold Rush. People became very rich or found nothing at all during this exciting time in history.
Physical properties
Gold is both ductile and malleable. Ductile means it can be drawn into thin wires. Malleable means capable of being hammered into thin sheets. A piece of gold weighing only 20 grams (slightly less than an ounce) can be hammered into a sheet that will cover more than 6 square meters (68 square feet). The sheet will be only 0.00025 centimeters (one ten-thousandth of an inch) thick. Gold foil of this thickness is often used to make the lettering on window signs.
Gold is quite soft. It can usually be scratched by a penny. Its melting point is 1,064.76°C (1,948.57°F) and its boiling point is about 2,700°C (4,900°F). Its density is 19.3 grams per cubic centimeter.
Two other important properties are its reflectivity and lack of electrical resistance. Both heat and light reflect off gold very well. But an electric current passes through gold very easily.
Chemical properties
Generally speaking, gold is not very reactive. It does not combine with oxygen or dissolve in most acids. It does not react with halogens, such as chlorine or bromine, very easily.
These chemical properties also account for some important uses of gold. Gold coins, for example, do not corrode (rust) or tarnish very easily. Neither does jewelry or artwork made of gold.
Occurrence in nature
Gold occurs in nature in both its native state and in compounds. The native state of an element is its free state. It is not combined with any other element. The most common compounds of gold are the tellurides. A telluride is a compound of the element tellurium and one or more other elements. For example, the mineral calavarite is mostly gold telluride (AuTe2).
At one time, gold was found in chunks or nuggets large enough to see. People mined gold by picking it out of streams and rivers. In fact, gold was once very common in some parts of the world. People valued it not because it was rare, but because it was so beautiful.
The abundance of gold in the Earth's crust is estimated to be about 0.005 parts per million. That makes it one of the ten rarest elements in the Earth's crust. Gold is thought to be much more common in the oceans. Some people believe as much as 70 million tons of gold are dissolved in seawater. They also think there may be another 10 billion tons on the bottom of the oceans. So far, however, no one has found a way to mine this gold.
About a quarter of the world's gold comes from South Africa. Other leading producers of the metal are the United States, Australia, Canada, China, and Russia. In the United States, about two-thirds of its gold is mined in Nevada. California, Montana, Alaska, and South Dakota also produce gold.
Isotopes
There is only one naturally occurring isotope of gold, gold-197. Isotopes are two or more forms of an element. Isotopes differ from each other according to their mass number. The number written to the right of the element's name is the mass number. The mass number represents the number of protons plus neutrons in the nucleus of an atom of the element. The number of protons determines the element, but the number of neutrons in the atom of any one element can vary. Each variation is an isotope.
About two dozen radioactive isotopes of gold are known also. A radioactive isotope is one that breaks apart and gives off some form of radiation. Radioactive isotopes are produced when very small particles are fired at atoms. These particles stick in the atoms and make them radioactive.
One radioactive isotope of gold is widely used in medicine, gold-198. This isotope has two major uses. First, it can be used to study the liver. It is made into a form known as colloidal gold. Colloidal gold consists of very fine particles of gold mixed in a liquid solution. The colloidal gold is injected into the patient's body, where it travels to the liver. There, it can be detected because of the radiation it gives off. The radiation can be used to tell if the liver is functioning normally or not.
Colloidal gold is also used to treat medical problems. In some forms of cancer, the body develops large amounts of liquid in the space around the stomach and intestines (the peritoneum). One way to treat this collection of liquid is with colloidal gold. The colloidal gold is injected into the peritoneum.
It is not able to Leave the peritoneum and go into the stomach and intestines. While in the peritoneum, the colloidal gold gives off radiation. The radiation kills cancer cells that cause the accumulation of fluid.
Extraction
There are at least two main ways to remove gold from its ores. One is to mix an ore with mercury metal. Mercury combines with gold in the ore to form an amalgam. An amalgam is a mixture of two or more metals, one of which is mercury. The gold amalgam is then removed from the ore. It is heated to drive off the mercury. Pure gold remains.
Gold ores can also be treated with potassium cyanide (KCN) or some other kind of cyanide. The gold combines with the cyanide to form a new compound, gold cyanate. The gold cyanate is then treated with an active metal, such as zinc. The active metal replaces gold in the compound, leaving pure gold.
Uses
In a 1986 study, experts estimated that 121,000 tons of gold had been mined throughout history. Of that amount, about 18,000 tons were used for industrial, research, health, and other "dissipative" uses. Dissipative means that the gold was gone once it was used. It was made into devices that were eventually thrown away. The gold could not or was not recovered from the devices.
Of the remaining 103,000 tons of gold, about a third (35,000 tons) had been made into gold bars held by national banks. The gold bars are used as security for national money systems. In the United States, for example, the nation's supply of gold is stored at Fort Knox, Kentucky.
Finally, the remaining 68,000 tons of gold are owned by private individuals. This gold exists in the form of jewelry, coins, or bullion. Gold bullion are bars or other large pieces of pure gold.
Jewelry is the largest single use of gold. In 1996, about 3,290 tons of gold were made worldwide. Of that amount, nearly 85 percent was made into jewelry. The second largest use of gold (about 213 tons, or about 7 percent) was in industrial devices and consumer products. Some examples include electrical contacts and switches, laboratory equipment, printed circuits, dental alloys, instruments on space vehicles, and nozzles used in the production of synthetic fibers.
Compounds
Few gold compounds have any important commercial uses.
Health effects
Gold is not required to maintain good health in plants or animals. It can be injected into a plant or animal without causing harmful effects. Some medical and commercial uses are based on this property.
Chemical Elements: From Carbon to Krypton
Copyright © 1999 by The Gale Group.
Published by The Gale Group. All rights reserved, including the right of reproduction in whole or in part in any form.
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