Silver

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	Silver

Notable Characteristics

Silver is a very ductile and malleable (slightly harder than gold) univalent coinage metal with a brilliant white metallic luster that can take a high degree of polish. It has the highest electrical conductivity of all metals, even higher than copper, but its greater cost has prevented it from being widely used in place of copper for electrical purposes.

Pure silver also has the highest thermal conductivity, whitest color, the highest optical reflectivity (although it is a poor reflector of ultraviolet), and the lowest contact resistance of any metal. Silver halides are photosensitive and are remarkable for the effect of light upon them. This metal is stable in pure air and water, but does tarnish when it is exposed to ozone, hydrogen sulfide, or air with sulfur in it. The most common oxidation states of silver are +1 and +2.

Applications

The principal use of silver is as a precious metal and its halide salts, especially silver nitrate, are also widely used in photography (which is the largest single end use of silver). Other uses;

Silver has many industrial applications such as in mirrors, electrical and electronic products.
Silver's catalytic properties make it ideal for use as a catalyst in oxidation reactions; for example, the production of formaldehyde from methanol and air by means of silver screens or crystallites[?] containing a minimum 99.95 weight-percent silver.
Sterling silver alloy (92.5% silver) is used for jewelry, silverware[?] and other places where appearance is important.
This metal is used in dental alloys that make fittings and fillings.
Used to make solder and brazing alloys, electrical contacts[?], and high capacity silver-zinc and silver-cadmium batteries.
Printed circuits are made using silver paints.
Silver fulminate[?] is a powerful explosive.
Silver chloride[?] can be made transparent and is used as a cement for glass.
Since 400 B.C. silver has been employed by many countries to make coins used in monetary exchange. In many languages the words for "silver" and "money" are the same.
Silver iodide[?] has been used in attempts to seed clouds to produce rain.

History

Silver (Anglo-Saxon, Seolfor siolfur; Ag is from the Latin argentum) has been known since ancient times. It is mentioned in the book of Genesis and slag heaps found in Asia Minor and on the islands of the Aegean Sea indicate that silver was being separated from lead as early as the 4th millennium BC.

Silver has been used for thousands of years as ornaments and utensils[?], for trade, and as the basis for many monetary systems[?]. It was long considered the second most precious metal, second only to gold, and was known under the name of luna to the ancients and alchemists. The alchemical symbol for silver is a half-moon with the open part on the left.

Europeans, found huge amount of silver in the New World, in Zacatecas, Mexico and Potosí, which triggered a period of inflation in Europe.

Argentina was named after the metal. Plata, as in Rio de la Plata is the Spanish word for silver

Occurrence

Silver is found in native form, combined with sulfur, arsenic, antimony, or chlorine and in various ores such as argentite[?] (Ag₂S) and horn silver[?] (AgCl). The principal sources of silver are copper, copper-nickel, gold, lead and lead-zinc ores obtained from Canada, Mexico, Peru, and the United States.

This metal is also produced during the electrolytic refining of copper. Commercial grade fine silver is at least 99.9% pure silver and purities greater than 99.999% are available.

Isotopes

Naturally occurring silver is composed of the two stable isotopes Ag-107 and Ag-109 with Ag-107 being the most abundant (51.839% natural abundance). Twenty-eight radioisotopes have been characterized with the most stable being Ag-105 with a half-life of 41.29 days, Ag-111 with a half-life of 7.45 days, and Ag-112 with a half-life of 3.13 hours. All of the remaining radioactive isotopes have half-lifes that are less than an hour and the majority of these have half lifes that are less than 3 minutes. This element also has numerous meta states with the most stable being Agm-128 (t_˝ 418 years), Agm-110 (t_˝ 249.79 days) and Agm-107 (t_˝ 8.28 days).

Isotopes of silver range in atomic weight from 93.943 amu (Ag-94) to 123.929 amu (Ag-124). The primary decay mode before the most abundant stable isotope, Ag-107, is electron capture and the primary mode after is beta decay. The primary decay products before Ag-107 are palladium (element 46) isotopes and the primary products after are cadmium (element 48) isotopes.

The palladium isotope Pd-107 decays by beta emission to Ag-107 with a half-life of 6.5 million years. Iron meteorites are the only objects with a high enough Pd/Ag ratio to yield measurable variations in Ag-107 abundance. Radiogenic Ag-107 was first discovered in the Santa Clara meteorite in 1978. The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. Pd-107 versus Ag correlations observed in bodies, which have clearly been melted since the accretion of the solar system, must reflect the presence of live short-lived nuclides in the early solar system.

Precautions

Silver itself isn't toxic but most of its salts are poisonous and may be carcinogenic. Compounds containing silver can be absorbed into the circulatory system and become deposited in various body tissues leading to the condition called argyria which results in a grayish skin pigmentation and mucus membranes. Silver has germicidal effects and kills many microbial organisms without causing noticeable harm to more complex life-forms. This metal plays no natural biological role in humans.

Production

Mexico is the largest silver producer. According to the Secretary of Economics of Mexico, it has produced in 2000, 2747 tons, about 15% of the annual production of the world.

External Links

WebElements.com - Silver (http://www.webelements.com/webelements/elements/text/Ag/index.html)
EnvironmentalChemistry.com - Silver (http://environmentalchemistry.com/yogi/periodic/Ag.html)

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