Silver (Environmental & Earth Science)
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Silver
Silver is the chemical element of atomic number 47; it is sometimes found in the Earth as the mineral native silver. Its chemical symbol is Ag, after the Latin word Argentum. Silver has a bright, metallic luster, and when untarnished, has a white color. Silver is found combined with a number of different elements to form a variety of minerals and ores. It is also found in very small amounts (called trace amounts) in gold, lead, zinc, and copper ores.
As a mineral, silver crystallizes in the cubic (isometric) system. In rare cases it forms crystals. Usually it is found in thin sheets or as long wires and bundles of wires. Silver is rather soft at 2 to 3 on Mohs' hardness scale. Like gold, it is malleable which means it can be hammered into thin sheets. It is also ductile, meaning it can be drawn into wire.
Silver has been known and used since ancient times. Evidence in Asia Minor suggests that people were separating silver from lead as long ago as 3000 BC. Like gold, it is a prized metal, both for its beauty and usefulness. Early coinage from silver emerged from Crete and some of the other Grecian islands as early as approximately 600 BC.
Name
| Previous Element: Palladium Next Element: Cadmium |
| |
| Physical Properties | ||
|---|---|---|
| Color | silvery | |
| Phase at Room Temp. | solid | |
| Density (g/cm3) | 10.49 | |
| Hardness (Mohs) | 3.25 | |
|
Melting Point (K) |
1235.1 | |
|
Boiling Point (K) |
2428 | |
| Heat of Fusion (kJ/mol) | 11.3 | |
| Heat of Vaporization (kJ/mol) | 258 | |
| Heat of Atomization (kJ/mol) | 284 | |
| Thermal Conductivity (J/m sec K) | 429 | |
| Electrical Conductivity (1/mohm cm) | 630.5 | |
| Source | Argentite (sulfide) | |
| Atomic Properties | ||
| Electron Configuration | [Kr]5s14d10 | |
|
Number of Isotopes |
59 (2 natural) | |
| Electron Affinity (kJ/mol) | 125.6 | |
| First Ionization Energy (kJ/mol) | 731 | |
| Second Ionization Energy (kJ/mol) | 2073.5 | |
| Third Ionization Energy (kJ/mol) | 3360.6 | |
| Electronegativity | 1.93 | |
| Polarizability (Å3) | 7.9 | |
| Atomic Weight | 107.87 | |
| Atomic Volume (cm3/mol) | 10.3 | |
| Ionic Radius2- (pm) | --- | |
| Ionic Radius1- (pm) | --- | |
| Atomic Radius (pm) | 144 | |
| Ionic Radius1+ (pm) | 129 | |
| Ionic Radius2+ (pm) | 108 | |
| Ionic Radius3+ (pm) | 89 | |
| Common Oxidation Numbers | +1 | |
| Other Oxid. Numbers | +2, +3 | |
| Abundance | ||
| In Earth's Crust (mg/kg) | 7.5x10-2 | |
| In Earth's Ocean (mg/L) | 4.0x10-5 | |
| In Human Body (%) | 0.000003% | |
| Regulatory / Health | ||
| CAS Number | 7440-22-4 | |
| OSHA Permissible Exposure Limit (PEL) | TWA: 0.01 mg/m3 | |
| OSHA PEL Vacated 1989 | TWA: 0.01 mg/m3 | |
|
NIOSH Recommended Exposure Limit (REL) |
TWA: 0.01 mg/m3 IDLH: 10 mg/m3 | |
|
Sources: |
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Silver was named from the Old English (Anglo-Saxon) word seolfer. This name is related to the German word silber and the Dutch word zilfer.
An early Latin name for this mineral was Luna which means moon, an allusion to its striking, bright luster.
Sources
Silver is found in lead, zinc, and copper ore deposits. A full two-thirds of the silver resources in the world are found in association with these other metal ores. The remaining third is found in association with deposits of gold.
The most important ore mineral of silver is argentite (Ag2S, silver sulfide).
In the United States, Nevada is the leading producer of silver where it is a by-product of gold mining. Other significant world producers of silver are Mexico, Peru, Chile, and Canada. A number of other countries produce smaller amounts of silver.
Human exposure
See main artcle: Health effects of silver
Most people are exposed daily to very low levels of silver chiefly in food and drinking water, and to lesser dosages in air. The silver in these exposures is partially due to naturally occurring silver in water and soil. Skin contact and breathing in air containing silver compounds also occurs in some industrial workplaces. Other sources of exposure include the use of silver in medicines, and in activities such as jewelry-making, soldering and photography. Exposure from everyday use, such as wearing jewelry or eating with silver-coated flatware, is not expected to result in any signiifant silver intake into the body.
Silver levels of less than 0.000001 mg silver per cubic meter of air or 0.2 to 2.0 parts silver per billion parts water (ppb) in surface waters, such as lakes and rivers, and 200 to 300 ppb in soils are found from naturally occurring sources. Silver compounds are also found in groundwater and at hazardous waste sites throughout the world. Drinking water supplies in the United States have been commonly found to contain silver levels of up to 80 ppb. Surveys show that one-tenth to one third of samples taken from drinking water supplies (both groundwater and surface water (Surface runoff of water)) contain silver at levels greater than 30 ppb.
Uses
Silver has been used for thousands of years for jewelry and decorative items of all types. Likewise, it has been used for silverware. Of all the metals, untarnished silver is the best reflector of light. As a result, it was used in ancient times to make mirrors. Unfortunately, silver tarnishes very easily and quickly, and its use as a mirror could be frustrating. Sterling silver is silver alloyed with another metal, usually copper. For such an alloy to be called “Sterling” it has to have 92.5% silver content. Silver is also used as a currency and at one time, along with gold, was the standard for the currency of the United States of America. Silver bromide and silver nitrate are used in photography. It is estimated that about one-third of the silver used in the United States is used in various photographic materials and processes. It is also used in electrical products because it conducts electricity so well (silver actually conducts electricity more efficiently than copper). It is used by dentists in amalgam fillings. Silver is also used in the production of bearings.
Substitutes and Alternative Sources
There are a number of materials and technologies that can be used in place of silver. Stainless steel is used to make tableware. Film with a lower silver content might be used in photography. Digital photography can conceivably significantly reduce the demand for silver-based films. Digital imaging will also reduce the consumption of silver-based films in the printing industry. Rhodium and aluminum can be substituted for silver in making mirrors.
Further Reading
- Common Minerals and Their Uses, Mineral Information Institute.
- More than 170 Mineral Photographs, Mineral Information Institute.
| Disclaimer: This article contains some information that was originally published by, the Mineral Information Institute. Topic editors and authors for the Encyclopedia of Earth have edited its content and added substantial new information. The use of information from the Mineral Information Institute should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content. |
