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Silver is a chemical element with symbol Ag ((ギリシア語:άργυρος) ''árguros'', (ラテン語:argentum), both from the Indo-European root '' *h₂erǵ-'' for "grey" or "shining") and atomic number 47. A soft, white, lustrous transition metal, it possesses the highest electrical conductivity, thermal conductivity and reflectivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a byproduct of copper, gold, lead, and zinc refining. Silver has long been valued as a precious metal. More abundant than gold, silver metal has in many premodern monetary systems functioned as coinable specie, sometimes even alongside gold. In addition, silver has numerous applications beyond currency, such as in solar panels, water filtration, jewelry and ornaments, high-value tableware and utensils (hence the term silverware), and also as an investment in the forms of coins and bullion. Silver is used industrially in electrical contacts and conductors, in specialized mirrors, window coatings and in catalysis of chemical reactions. Its compounds are used in photographic film and X-rays. Dilute silver nitrate solutions and other silver compounds are used as disinfectants and microbiocides (oligodynamic effect), added to bandages and wound-dressings, catheters and other medical instruments. ==Characteristics== Silver is produced during certain types of supernova explosions by nucleosynthesis from lighter elements through the r-process, a form of nuclear fusion that produces many elements heavier than iron, of which silver is one. Silver is a very ductile, malleable (slightly less so than gold), univalent coinage metal, with a brilliant white metallic luster that can take a high degree of polish. Protected silver has higher optical reflectivity than aluminium at all wavelengths longer than ~450 nm. At wavelengths shorter than 450 nm, silver's reflectivity is inferior to that of aluminium and drops to zero near 310 nm.〔(【引用サイトリンク】title=Silver vs. Aluminum )〕 The electrical conductivity of silver is the highest of all metals, even higher than copper, but it is not widely used for electrical purposes due to its much higher cost. An exception to this is in radio-frequency engineering, particularly at VHF and higher frequencies, where silver plating is employed to improve electrical conductivity of parts and wires (at high frequencies current tends to flow on the surface of conductors, not their interior, hence silver plating greatly improves overall conductivity). Silver also has the lowest contact resistance of any metal. During World War II in the US, 13,540 tons were used in the electromagnets used for enriching uranium, mainly because of the wartime shortage of copper. Pure silver has the highest thermal conductivity of any metal, although those of the nonmetal carbon in the form of diamond and Superfluid helium-4 are higher. Silver halides are photosensitive and are remarkable for their ability to record a latent image that can later be developed chemically. Silver is stable in pure air and water, but tarnishes when it is exposed to air or water containing ozone or hydrogen sulfide, the latter forming a black layer of silver sulfide, which can be cleaned off with dilute hydrochloric acid.〔 The most common oxidation state of silver is +1 (for example, silver nitrate, AgNO3); the less common +2 compounds (for example, silver(II) fluoride, AgF2), and the even less common +3 (for example, potassium tetrafluoroargentate(III), KAgF4) and even +4 compounds (for example, potassium hexafluoroargentate(IV), K2AgF6) are also known. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「silver」の詳細全文を読む スポンサード リンク
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