Encyclopedia > Gold (color)

Gold is a chemical element in the periodic table that has the symbol Au (L. aurum) and atomic number 79. A soft, shiny, yellow, heavy, malleable, ductile (trivalent and univalent) transition metal, gold does not react with most chemicals but is attacked by chlorine and aqua regia. The metal occurs mainly uncombined as nuggets in rocks and alluvial deposits and is one of the coinage metals. Gold is used as a monetary standard for many nations and is also used in jewelry, dentistry, and in electronics.

Table of contents

1 Notable characteristics

2 Applications

3 History

3.1 Value

Notable characteristics Gold is a metallic element that exhibits a yellow color en mass but can be black, ruby, or purple when finely divided. It is arguably the most beautiful of all the elements and is the most malleable and ductile metal known. In fact, 1 oz. of gold can be hammered into a sheet that covers 300 square feet. A soft metal, gold is often alloyed with other metals to give it more strength.

Gold is also a good conductor of heat and electricity and is not affected by air and most reagents. It is quite chemically unalterable by heat, moisture, and most corrosive agents and therefore is well suited for its use in coin and jewelry.

The color of solid gold as well as of the intensely colored, often purple, colloidal solutions that can be made from it is caused by the fact that the plasmon frequency of this element lies in the visible range, which causes red and yellow light to be reflected and blue light to be absorbed. Native gold contains usually eight to ten per cent silver, but often much more. As the amount of silver increases, the color becomes whiter and the specific gravity lower.

Alloys with with copper yield a redder metal, alloys with iron are green, aluminum alloys are purple. Jewelry made with combinations of colored gold is sold in the western United States to the tourist trade as Black Hills gold.

Common oxidation states of gold include +1 and +3. Applications Pure gold is too soft for ordinary use and is hardened by alloying with silver and copper. Gold and its many alloys are most often used in jewelry, coinage and as a standard for monetary exchange in many countries. Because of its superior electrical conductivity and resistance to corrosion and other desirable combinations of physical and chemical properties, gold also emerged in the late 20th century as an essential industrial metal. Other uses;

Gold performs critical functions in computers, communications equipment, spacecraft, jet aircraft engines, and a host of other products.
The high electrical conductivity and resistance to oxidation of gold has led to its widespread use as thin layers electroplated on the surface of electrical connectors to ensure a good, low-resistance connection.
Like silver, gold can form a hard amalgam with mercury, and is sometimes used for dental fillings[?].
Colloidal gold (gold nanoparticles) is an intensely colored solution that is currently studied in many labs for medical and biological applications. It is also the form used as gold paint on ceramics prior to firing.
Chlorauric acid is used in photography for toning the silver image.
Disodium aurothiomalate is a treatment for rheumatoid arthritis (administered intramuscularly).
The gold isotope Au-198, (half-life: 2.7 days) is used in some cancer treatments and for treating other diseases.
Gold is used as a coating enabling biological material to be viewed under a scanning electron microscope.
Gold is often symbolic for the highest or best achievement. Like a blue ribbon[?], a gold medal is the highest award in the Olympics and many other competitions.

Since it is a good reflector of both infrared and is inert light, it is used for the protective coatings on many artificial satellites. History Gold (Sanskrit Jval; Anglo-Saxon gold; Latin aurum all meaning "gold") has been known and highly valued since ancient times. Egyptian hieroglyphs from 2600 BC describe the metal and gold is mentioned several times in the Old Testament.

Gold has long been considered one of the most precious metals, and its value has been used as the standard for many currencies (known as the gold standard) in history.

The primary goal of the alchemists was to produce gold from other substances, such as lead - Though they were never successful at this attempt, the alchemists promoted an interest in what can be done with substances, and this laid a foundation for today's chemistry. Many competitions award a gold medal[?] to the winner, silver to the second-place finisher, and bronze to the third. The largest gold depository in the world is the U.S. Federal Reserve Bank.

Value

Like other precious metals, gold is measured by troy weight and when it is alloyed with other metals the term carat is used to indicate the amount of gold present with 24 carats being pure gold.

Historical gold was used to back currency in a system known as the gold standard in which one unit of currency was equivalent to a certain amount of gold.

For a very long time the value of gold was set by the United States at $20.67 per troy ounce but in 1934 the value of gold was fixed at $35.00 per troy ounce. Because of a gold crisis, on March 17, 1968, a two-tiered pricing scheme was established whereby gold was still used to settle international accounts at the old $35.00 per troy ounce but the price of gold on the private market was allowed to fluctuate, this two-tiered pricing system was abandoned in 1975 when the price of gold was allowed to fluctuate. Since 1968 the price of gold on the open market has widely fluctuated reaching $620/troy oz. in January 1980 but later dropped to $410/troy oz by January 1990.

Because of its use as a reserve store of value, the possession of gold is sometimes restricted or banned. Within the United States, the private possession of gold except as jewelry and coin collecting was banned between 1933 and 1975.

As an investment gold is not highly regarded in normal times, because it pays no dividends. However, gold becomes desirable in times of extremely weak confidence and during hyperinflation because gold maintains its value even as all other investments become worthless. Occurrence Due to its relative chemical inertness, gold often is found as the native metal, occasionally as large nuggets, but usually as minute flakes in some minerals, quartz veins, slate, metamorphic rocks and in alluvial deposits that originated from these sources. Gold is widely distributed, is very often associated with the minerals quartz or pyrite and is combined with tellurium in the minerals petzite[?], calaverite[?] and sylvanite[?]. Gold is extracted from alluvium by techniques of placer mining[?]. South Africa is the source for about two-thirds of the world's gold supply (mines in South Dakota and Nevada supply two-thirds of gold used in the United States).

Gold is extracted from ores through the use of cyanide, amalgam, and smelting. Refining of the metal is frequently accomplished by electrolysis. This metal occurs in sea water at 0.1 to 2 mg/ton depending sample location. However, there is no profitable method for recovering gold from sea water yet.

Although gold is important to industry and the arts, it also retains a unique status among all commodities as a long-term store of value. It has been estimated that all the gold in the world that has been refined could form a single cube 60 ft. on a side. Compounds Auric chloride (AuCl₃) and chlorauric acid (HAuCl₄) are the most common compounds of gold. Although gold is a noble metal it can form many compounds

It dissolves in Aqua regia to form the AuCl₄^- ion
Gold halides (F,Cl,Br,I)
Gold chalcogenides (O, S, Se,Te)
Gold cluster compounds[?]

Isotopes There is only one stable isotope of gold, and 18 radioisotopes with Au-195 being the most stable with a half-life of 186 days. Precautions The human body does not absorb this metal well and compounds of gold are not normally very toxic. Liver and kidney damage has, however, been reported for up to 50% of arthritis patients treated with gold-containing drugs. External links

WebElements.com - Gold (http://www.webelements.com/webelements/elements/text/Au/index)
EnvironmentalChemistry.com - Gold (http://environmentalchemistry.com/yogi/periodic/Au)
Gold as non-government issued (http://www.e-gold.com/) electronic money
Gold prices and economy (http://www.kitco.com)

Gold is also a color, a shade of yellow.

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