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silver tea caddy, 1767–68
Silver tea caddy with maker"s mark C.N., hallmark for 1767–68, London; in the Victoria và Albert Museum, London.
Courtesy of the Victoria and Albert Museum, London; photograph, A.C. Cooper Ltd.
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Silver ornaments & decorations have been found in royal tombs dating back as far as 4000 bce. It is probable that both gold và silver were used as money by 800 bce in all countries between the Indus và the Nile.
Alexander the Great
Alexander the Great as Zeus Ammon on a silver tetradrachm of Lysimachus, 297–281 bce, thought to lớn be a copy of a portrait by Lysippus; in the British Museum. Diameter 30 mm.
Reproduced with permission of the trustees of the British Museum; photograph, Ray Gardner for The Hamlyn Publishing Group Limited
Silver is widely distributed in nature, but the total amount is quite small when compared with other metals; the metal constitutes 0.05 part per million of Earth’s crust. Practically all sulfides of lead, copper, & zinc contain some silver. Silver-bearing ores may contain amounts of silver from a trace khổng lồ several thousand troy ounces per avoirdupois ton, or about 10 percent.
Unlike gold, silver is present in many naturally occurring minerals. For silver the more important deposits commercially are such compounds as the minerals tetrahedrite and argentite (silver sulfide, Ag2S), which is usually associated with other sulfides such as those of lead & copper, as well as several other sulfides, some of which contain antimony as well. Silver is found generally in lead ores, copper ores, & cobalt arsenide ores & is also frequently associated with gold in nature. Most silver is derived as a by-product from ores that are mined và processed to obtain these other metals. Deposits of native (chemically free, or uncombined) silver are also commercially important.
| *Estimate. | ||||
| **Includes silver obtainable from base-metal ores. | ||||
| ***Detail does not địa chỉ to total given because of rounding. | ||||
| Source: U.S. Department of the Interior, Mineral Commodity Summaries 2017. | ||||
| Mexico | 5,600 | 20.7 | 37,000 | 6.5 |
| Peru | 4,100 | 15.2 | 120,000 | 21.1 |
| china | 3,600 | 13.3 | 39,000 | 6.8 |
| Chile | 1,500 | 5.6 | 77,000 | 13.5 |
| nước australia | 1,400 | 5.2 | 89,000 | 15.6 |
| Poland | 1,400 | 5.2 | 85,000 | 14.9 |
| Russia | 1,400 | 5.2 | 20,000 | 3.5 |
| Bolivia | 1,300 | 4.8 | 22,000 | 3.9 |
| United States | 1,100 | 4.1 | 25,000 | 4.4 |
| other countries | 5,400 | đôi mươi | 57,000 | 10 |
| world total | 27,000 | 100*** | 570,000 | 100*** |
Historically, a major use of silver has been monetary, in the form of reserves of silver bullion & in coins. By the 1960s, however, the demand for silver for industrial purposes, in particular the photographic industry, exceeded the total annual world production. In the early 21st century, digital cameras supplanted those that used film, but demand for silver from other sectors—such as for sterling and plated silverware, ornaments, jewelry, coinage, electronic components, và photovoltaic cells—continued lớn be important.
Alloys of silver with copper are harder, tougher, and more fusible than pure silver & are used for jewelry and coinage. The proportion of silver in these alloys is stated in terms of fineness, which means parts of silver per thousand of the alloy. Sterling silver contains 92.5 percent of silver và 7.5 percent of another metal, usually copper; i.e., it has a fineness of 925. Jewelry silver is an alloy containing 80 percent silver and 20 percent copper (800 fine). The yellow gold that is used in jewelry is composed of 53 percent gold, 25 percent silver, and 22 percent copper. (For treatment of silver’s use in ornamental and household objects, see metalwork.)
Natural silver consists of a mixture of two stable isotopes: silver-107 (51.839 percent) & silver-109 (48.161 percent). The metal does not react with moist air or dry oxygen but is oxidized superficially by moist ozone. It is quickly tarnished at room temperature by sulfur or hydrogen sulfide. In the molten state, silver can dissolve up lớn 22 times its volume of oxygen; on solidification, most of the oxygen is expelled, a phenomenon known as the spitting of silver. This can be controlled by the addition of a deoxidant such as charcoal khổng lồ the molten silver. Silver dissolves readily in nitric acid & in hot concentrated sulfuric acid. The metal will also dissolve in oxidizing acids & in solutions containing cyanide ions in the presence of oxygen or peroxides. Dissolution in cyanide solutions is attributable to the formation of the very stable dicyanoargentate,
Like copper, silver has a single s electron outside a completed d shell, but, in spite of the similarity in electronic structures và ionization energies, there are few close resemblances between silver and copper.
Compounds
For silver the preeminently important oxidation state in all of its ordinary chemistry is the state +1, although the states +2 and +3 are known.
Silver compounds include silver chloride (AgCl), silver bromide (AgBr), and silver iodide (AgI). Each of these salts is used in photography. Silver chloride serves as the light-sensitive material in photographic printing papers and, together with silver bromide, in certain films & plates. The iodide is also used in the manufacture of photographic papers and films, as well as in cloud seeding for artificial rainmaking và in some antiseptics. All three halides are derived from silver nitrate (AgNO3), which is the most important of the inorganic silver salts. Besides these other salts, silver nitrate is also the starting material for the production of the silver cyanide used in silver plating.
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