Silver is a chemical element with the symbol Ag (from Latin: argentum, derived from the Proto-Indo-European root h₂erǵ-, meaning "shining" or "white") and atomic number 47. A soft, white, lustrous transition metal, it exhibits the highest electrical conductivity, thermal conductivity, and reflectivity of any metal.
Properties Silver is a highly ductile and malleable metal, second only to gold in its malleability. Its characteristic metallic luster is bright and reflects light very efficiently. Silver readily tarnishes in the presence of sulfur compounds, forming a black layer of silver sulfide. It is stable in pure air and water but is attacked by nitric acid and hot concentrated sulfuric acid. Silver has a melting point of 961.78 °C and a boiling point of 2162 °C. Its density is 10.49 g/cm³.
Occurrence and Production Silver occurs in native form (pure silver), but more commonly in various ores, often in association with other metals like copper, lead, and zinc. Major silver-bearing minerals include argentite (Ag₂S), chlorargyrite (AgCl), and polybasite. Most silver today is produced as a byproduct of mining and refining copper, lead, zinc, and gold ores. Significant silver deposits are found in Mexico, Peru, China, Australia, and Russia.
History Silver has been known and valued by humans since ancient times, with evidence of its use dating back to 3000 BCE in Egypt, Anatolia, and Mesopotamia. Its luster and relative scarcity made it highly prized for ornamentation, jewelry, coinage, and religious artifacts. Ancient civilizations developed sophisticated methods for refining silver from its ores. Historically, silver played a crucial role as a monetary standard in many economies, often alongside gold.
Uses Silver's unique combination of properties makes it indispensable in a wide array of applications:
- Jewelry and Decorative Items: Due to its beauty and malleability, silver is widely used in jewelry, silverware, and decorative objects. Sterling silver, an alloy of 92.5% silver and 7.5% copper, is a popular choice for these items, offering greater durability.
- Coinage and Investment: Historically a primary material for coins, silver continues to be used in commemorative coins and as an investment in the form of bullion (bars and rounds).
- Electronics and Electrical Applications: Silver's exceptional electrical conductivity makes it vital for electrical contacts, conductors, and printed circuit boards, particularly in high-reliability applications.
- Photography: Silver halides (e.g., silver bromide, silver chloride) are light-sensitive and form the basis of traditional photographic film and paper. Although digital photography has reduced its use, it remains relevant in specialized photographic processes.
- Mirrors and Optics: Silver's high reflectivity makes it an excellent coating for mirrors and optical devices.
- Catalysis: Silver acts as a catalyst in various industrial chemical reactions, such as the production of ethylene oxide.
- Medicine: Silver and its compounds have antimicrobial properties. Silver sulfadiazine is used in burn creams, and silver nanoparticles are incorporated into medical devices and wound dressings to prevent infection. Colloidal silver has also been used, though its efficacy and safety are debated.
- Water Purification: Silver ions can be used to purify water by inhibiting bacterial growth.
Alloys The most common silver alloy is sterling silver, consisting of 92.5% silver and 7.5% copper. Other metals can be added in smaller amounts to improve specific properties like hardness or resistance to tarnish. Amalgams used in dentistry historically contained silver, though their use has declined.