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Silver

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                47              palladium ← silver → cadmium
                Cu
                ↑
                Ag
                ↓
                Au

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                       Name, Symbol, Number silver, Ag, 47
                                         Chemical series transition metals
                                             Group, Period, Block 11, 5, d
                                           Appearance lustrous white metal
                                            Atomic mass 107.8682 (2) g/mol
                                    Electron configuration [Kr] 4d^10 5s^1
                                       Electrons per shell 2, 8, 18, 18, 1
                                                       Physical properties
                                                             Colour silver
                                                               Phase solid
                                      Density (near r.t.) 10.49 g·cm^−3
                                   Liquid density at m.p. 9.320 g·cm^−3
                                                  Melting point 1234.93  K
                                                (961.78 ° C, 1763.2 ° F)
                                                      Boiling point 2435 K
                                                    (2162 ° C, 3924 ° F)
                                         Heat of fusion 11.28 kJ·mol^−1
                                     Heat of vaporization 258 kJ·mol^−1
                         Heat capacity (25 °C) 25.350 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 1283 1413 1575 1782 2055 2433

                                                         Atomic properties
                                     Crystal structure face-centered cubic
                                                        Oxidation states 1
                                                       ( amphoteric oxide)
                                    Electronegativity 1.93 (Pauling scale)
                                     Ionization energies 1st: 731.0 kJ/mol
                                                          2nd: 2070 kJ/mol
                                                          3rd: 3361 kJ/mol
                                                      Atomic radius 160 pm
                                              Atomic radius (calc.) 165 pm
                                                    Covalent radius 153 pm
                                               Van der Waals radius 172 pm
                                                             Miscellaneous
                                             Magnetic ordering diamagnetic
                              Electrical resistivity (20 °C) 15.87 nΩ·m
                        Thermal conductivity (300 K) 429 W·m^−1·K^−1
                                   Thermal diffusivity (300 K) 174 mm²/ s
                       Thermal expansion (25 °C) 18.9 µm·m^−1·K^−1
                        Speed of sound (thin rod) ( r.t.) 2680   m·s^−1
                                                    Young's modulus 83 GPa
                                                      Shear modulus 30 GPa
                                                      Bulk modulus 100 GPa
                                                        Poisson ratio 0.37
                                                         Mohs hardness 2.5
                                                  Vickers hardness 251 MPa
                                                 Brinell hardness 24.5 MPa
                                             CAS registry number 7440-22-4
                                                         Selected isotopes

                  CAPTION: Main article: Isotopes of silver

                         iso      NA    half-life DM    DE ( MeV)     DP
                       ^105Ag   syn     41.2 d    ε   -             ^105Pd
                                                  γ   0.344, 0.280,
                                                      0.644, 0.443  -
                       ^106 mAg syn     8.28 d    ε   -             ^106Pd
                                                  γ   0.511, 0.717,
                                                      1.045, 0.450  -
                       ^107Ag   51.839% Ag is stable with 60 neutrons
                       ^108 mAg syn     418 y     ε   -             ^108Pd
                                                  IT  0.109         ^108Ag
                                                  γ   0.433, 0.614,
                                                      0.722         -
                       ^109Ag   48.161% Ag is stable with 62 neutrons
                       ^111Ag   syn     7.45 d    β^- 1.036, 0.694  ^111Cd
                                                  γ   0.342         -

                                                                References

   Silver ( IPA: /ˈsɪlvə/) is a chemical element with the symbol Ag (
   Latin: argentum). A soft white lustrous transition metal, it has the
   highest electrical and thermal conductivity of any metal and occurs in
   minerals and in free form. This metal is used in coins, jewelry,
   tableware, photography, and in mirrors.

Notable characteristics

   A nugget of silver
   Enlarge
   A nugget of silver

   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 and tarnishability has prevented it from being widely used in
   place of copper for electrical purposes.

   Pure silver also has the highest thermal conductivity, whitest colour,
   the highest optical reflectivity (although it is a poor reflector of
   ultraviolet light), 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
   containing sulfur. The most common oxidation state of silver is +1 (for
   example, silver nitrate; AgNO[3]); a few +2 (for example, silver(II)
   fluoride; AgF[2]) and +3 compounds (for example, silver(III)
   persulfate; Ag[2](SO[5])[3]) are also known.

Applications

   The principal use of silver is as a precious metal. Its salts,
   especially silver nitrate and silver halides, are also widely used in
   photography (which is the largest single end use of silver). Some other
   uses for silver are as follows:
     * Electrical and electronic products, which need silver's superior
       conductivity, even when tarnished. For example, printed circuits
       are made using silver paints, and computer keyboards use silver
       electrical contacts. Silver (silver cadmium oxide) is also used in
       high voltage contacts because it can minimize any arcing.
     * Mirrors which need superior reflectivity for visible light are made
       with silver as the reflecting material in a process called
       silvering. Common mirrors are backed with aluminium.
     * Many high end musical instruments are made with silver, which
       benefit from a higher tone quality.
     * Silver has been coined to produce money since 700 BC by the
       Lydians, in the form of electrum. Later, silver was refined and
       coined in its pure form. The words for "silver" and "money" are the
       same in at least 14 languages.
     * The metal is chosen for its beauty in the manufacture of jewelry
       and silverware, which are traditionally made from the silver alloy
       known as Sterling silver, which is 92.5% silver and usually alloyed
       with copper. The name of United Kingdom monetary unit 'Pound'
       originally had the value of one troy pound of sterling silver.
     * Silver is also used in medals, denoting second place.
     * The malleability, non-toxicity and beauty of silver make it useful
       in dental alloys for fittings and fillings.
     * 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. Silver (upon some
       suitable support) is probably the only catalyst available today to
       convert ethylene to ethylene oxide (later hydrolyzed to ethylene
       glycol, used for making polyesters)—a very important industrial
       reaction.
     * Oxygen dissolves in silver relatively easily compared to other
       gases present in air. Attempts have been made to construct silver
       membranes of only a few monolayers thickness. Such a membrane could
       be used to filter pure oxygen from air.
     * Used to make solder and brazing alloys, electrical contacts, and
       high capacity silver-zinc and silver-cadmium batteries.
     * Silver sulfide, also known as Silver Whiskers, is formed when
       silver electrical contacts are used in an atmosphere rich in
       hydrogen sulfide.
     * Silver fulminate is a powerful explosive.
     * Silver chloride can be made transparent and is used as a cement for
       glass.
     * Silver chloride is also a widely used electrode for pH testing and
       potentiometric measurement.
     * Silver iodide has been used in attempts to seed clouds to produce
       rain.
     * Silver oxide is used as a positive electrode ( cathode) in watch
       batteries.
     * Colloidal silver is a possible antibacterial / antibiotic treatment
       espoused in alternative medicine, also notorious for causing
       argyria.
     * Silver nitrate (liquid) was a standard of care but was largely
       replaced by silver sulfadiazine cream (SSD Cream) which was
       generally the "standard of care" for the antibacterial/antibiotic
       treatment of serious burns until the late 1990's. Now, other
       options such as silver coated dressings (activated silver
       dressings) are used in addition to SSD cream, and may present
       advantages such as pain reduction and capacity for treatment at
       home.
     * Silver is often used in modern horror fiction as a weapon against
       certain supernatural entities, especially werewolves, who are
       sometimes described as being burned by silver.

History

   Alchemical symbol for silver
   Enlarge
   Alchemical symbol for silver

   Silver (from Anglo-Saxon seolfor, compare Old High German silabar; 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 for ornaments and utensils,
   for trade, and as the basis for many monetary systems. Its value as a
   precious metal was long considered second only to gold. In Ancient
   Egypt and Medieval Europe, it was often more valuable than gold.

   Judas Iscariot is infamous for having, according to the New Testament,
   taken a bribe of thirty pieces of silver from religious leaders in
   Jerusalem to turn Jesus Christ over to the Romans.

   Associated with the moon, as well as with the sea and various lunar
   goddesses, the metal was referred to by alchemists by the name luna.
   One of the alchemical symbols for silver is a crescent moon with the
   open part on the left (see picture, left).

   The metal mercury was thought of as a kind of silver, though the two
   elements are chemically unrelated; its Latin and English names,
   hydrargyrum ("watery silver") and quicksilver, respectively, reflect
   this history.

   In heraldry, the argent, in addition to being shown as silver (this has
   been shown at times with real silver in official representations), can
   also be shown as white. Occasionally, the word "silver" is used rather
   than argent; sometimes this is done across-the-board, sometimes to
   avoid repetition of the word "argent" in blazon.

   Europeans found a huge amount of silver in the New World in Zacatecas
   and Potosí, which triggered a period of inflation in Europe. The
   conquistador Pizarro was said to have resorted to having his horses
   shod with silver horseshoes due to the metal's abundance, in contrast
   to the relative lack of iron in Peru. Silver, which was extremely
   valuable in China, became a global commodity, contributing to the rise
   of the Spanish Empire. The rise and fall of its value affected the
   world market.

   The Rio de la Plata was named after silver (in Spanish, plata), and in
   turn lent the meaning of its name to Argentina.

   Silver mining was a driving force in the settlement of western North
   America, with major booms for silver and associated minerals (primarily
   lead) in the galena ore silver is most commonly found in. Notable
   "silver rushes" were in Colorado, Nevada, Cobalt, Ontario , California
   and the Kootenay region of British Columbia, notably in the Boundary
   and "Silvery Slocan". The largest silver ore deposits in the United
   States were discovered at the Comstock Lode in Virginia City, Nevada,
   in 1859.

Occurrence and extraction

   Silver ore (Lincoln cent is shown for scale)
   Enlarge
   Silver ore (Lincoln cent is shown for scale)

   Silver is found in native form, combined with sulfur, arsenic,
   antimony, or chlorine and in various ores such as argentite (Ag[2]S)
   and horn silver (AgCl). The principal sources of silver are copper,
   copper-nickel, gold, lead and lead-zinc ores obtained from Canada,
   Cobalt, Ontario, Mexico (historically Batopilas), Peru, Australia 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. Mexico is the world's largest
   silver producer. According to the Secretary of Economics of Mexico, it
   produced 80,120,000 troy ounces (2492 metric tons) in 2000, about 15%
   of the annual production of the world.

Price

   Johnson Matthey silver bullion bar
   Enlarge
   Johnson Matthey silver bullion bar

   Silver is currently about 1/50th the price of gold by mass, and
   approximately 70 times more valuable than copper. Silver did once trade
   at 1/6th to 1/12th the price of gold, prior to the Age of Discovery and
   the discovery of great silver deposits in the Americas, most notably
   the vast Comstock Lode in Virginia City, Nevada, USA. This then
   resulted in the debate over cheap Free Silver to benefit the
   agricultural sector was among the most prolongued and difficult in that
   country's history and dominated public discourse during the latter
   decades of the nineteenth century.

   Over the last 100 years the price of silver and the gold/silver price
   ratio has fluctuated greatly due to competing industrial and store of
   value demands. In 1980 the silver price rose to an all-time high of
   US$49.45 per troy ounce. By December 2001 the price had fallen to
   US$4.15 per ounce, and in May 2006 it had risen back as high as
   US$15.21 per ounce. As of 2006, current silver prices (and most other
   metal prices) have been rather volatile, for example quickly dropping
   from the May high of US$15.21 per ounce to a June low of US$9.60 per
   ounce before rising back above US$12 per ounce by August.

Isotopes

   Naturally occurring silver is composed of the two stable isotopes
   ^107Ag and ^109Ag with ^107Ag being the more abundant (51.839% natural
   abundance). Twenty-eight radioisotopes have been characterised with the
   most stable being ^105Ag with a half-life of 41.29 days, ^111Ag with a
   half-life of 7.45 days, and ^112Ag 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 ^108mAg (t[*] 418 years), ^110mAg (t[*] 249.79 days)
   and ^106mAg (t[*] 8.28 days).

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

   The palladium isotope ^107Pd decays by beta emission to ^107Ag 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 ^107Ag
   abundance. Radiogenic ^107Ag 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. ^107Pd 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.

In medicine

   Hippocrates, the father of modern medicine, wrote that silver had
   beneficial healing and anti-disease properties, and the Phoenicians
   used to store water, wine, and vinegar in silver bottles to prevent
   spoiling. In the early 1900s people would put silver dollars in milk
   bottles to prolong the milk's freshness. Silver compounds were used
   successfully to prevent infection in World War I before the advent of
   antibiotics.

   The widespread use of silver went out of fashion with the development
   of modern antibiotics. However, recently there has been renewed
   interest in silver as a broad spectrum antimicrobial. In particular, it
   is being used with alginate, a naturally occurring biopolymer derived
   from seaweed, in a range of silver alginate products designed to
   prevent infections as part of wound management procedures, particularly
   applicable to burn victims. In addition, Samsung has introduced washing
   machines with a final rinse containing silver ions to provide several
   days of antibacterial protection in the clothes. Additionally, Kohler
   has introduced a line of toilets that have silver ions embedded in the
   porcelain to kill germs.

Health precautions

   Silver plays no known natural biological role in humans, and possible
   health effects of silver are a subject of dispute. Silver itself is not
   toxic but most silver salts are, and some may be carcinogenic.

   Silver and compounds containing silver (like colloidal silver) can be
   absorbed into the circulatory system and become deposited in various
   body tissues leading to a condition called argyria which results in a
   blue-grayish pigmentation of the skin, eyes, and mucous membranes.
   Although this condition does not harm a person's health, it is
   disfiguring and usually permanent. Argyria is rare and mild forms are
   sometimes mistaken for cyanosis.

   Silver-ions and silver compounds show a toxic effect on some bacteria,
   viruses, algae and fungi typical for heavy metals like lead or mercury,
   but without the high toxicity to humans that is normally associated
   with them. Its germicidal effects kills many microbial organisms in
   vitro (i.e. in a test tube or a petri dish). The exact process by which
   this is done is still not well understood, although several different
   theories exist. One of these is a process generally known for heavy
   metals called the oligodynamic effect, which goes a long way explaining
   the effect on microbial lifeforms but does not explain certain
   antiviral functions.

Alternative medicine

   Today, various kinds of silver compounds, or devices to make solutions
   or colloids containing silver, are sold as remedies for a wide variety
   of diseases. Although mostly harmless, some people using these
   home-made solutions use far too much and develop argyria over a period
   of months or years, and several have been documented in the last few
   years in the medical literature, including one possible case of coma
   associated with a high intake of silver (see medical references). It is
   strongly advised to notify a doctor when taking silver as a form of
   self-medication.

In food

   In India, foods can be found decorated with a thin layer of silver,
   known as Varak. Silver as a food additive is given the E number E174
   and classed as a food coloring. It is used solely for external
   decoration, such as on chocolate confectionery, in the covering of
   dragées and the decoration of sugar-coated flour confectionery. In
   Australia, it is banned as a food additive.

Superstition

   Because of the mysticism surrounding silver's lunar associations, as
   well as the aesthetic qualities of the white, reflective metal that
   cause it to be associated with purity, silver in European Folklore has
   long been traditionally believed to be an antidote to various maladies
   and fictional monsters. Notably, silver was believed to be a repellant
   against vampires (this primarily originates from its holy connotations;
   also, mirrors were originally polished silver, and as such, vampires
   allegedly cannot be seen in them because they are wicked) and it was
   believed that a werewolf, in his bestial form, could only be killed by
   a weapon or bullet made of silver, and was equally effective against
   vampires, as described in Eastern European folklore. This has given
   rise to the term " silver bullet," which is used to describe things
   that very effectively deal with one specific problem.
   Retrieved from " http://en.wikipedia.org/wiki/Silver"
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   with only minor checks and changes (see www.wikipedia.org for details
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