47
  Ag  
107.868200
Silver

Name: Silver
Symbol: Ag
Atomic Number: 47
AtomicWeight: 107.868200
Family: Transition Metals
CAS RN: 7440-22-4
Description: A soft,  ductile and malleable metal.
State (25C): Solid
Oxidation states: +1, +2, +3

Molar Volume: 10.27 cm3/mole
Valence Electrons: 5s1

Boiling Point:  2436K, 2163C, 3925F
Melting Point:
1234K, 961C, 1762F
Electrons Energy Level: 2, 8, 18, 18, 1
Isotopes: 36 + 2 Stable
Heat of Vaporization: 250.58 kJ/mol
Heat of Fusion: 11.3 kJ/mol
Density: 10.5 g/cm3 @ 300K
Specific Heat: 0.235 J/gK
Atomic Radius: 1.75
Ionic Radius: 1.26
Electronegativity: 1.93 (Pauling); 1.42 (Allrod Rochow)
Vapor Pressure: 0.342 Pa @ 961C

1s2 2s2p6 3s2p6d10 4s2p6d10 5s1

History

Silver (from Turkic,  ilbir (chain); through Ango-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, B.C.

Silver has been used for thousands of years for ornaments and utensils, for trade, and as the basis for monetary systems.  Its value as a precious was long considered second only to gold.  In Ancient Egypt and Medieval Europe, it was often more valuable than gold.

Judas 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.

75px-silver-symbol.jpg (2800 bytes)

Alchemical symbol for Silver.

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.

luna.jpg (1236 bytes) silver1.jpg (1281 bytes) silver2.jpg (1288 bytes) silver3.jpg (1443 bytes) silver4.jpg (1343 bytes) silver5.jpg (1394 bytes)
silver6.jpg (1458 bytes) silver7.jpg (1619 bytes) silver8.jpg (1273 bytes) silver9.jpg (1549 bytes) silver10.jpg (1644 bytes) silver11.jpg (1244 bytes)

Additional Representations of Alchemical Symbols for Silver

Europeans found a huge amount of silver in the New World in Zacatecas and Potosi, 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 in which silver is most commonly found.  Notable "silver rushes" were in Colorado; Nevada; Cobalt, Ontario, Canada; 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.  In the Coeur d'Alene mining disctrict of northern Idaho the world-famous Sunshine Mine, the richest silver mine in American history, has had more than 350 million ounces of production over the past century. At the time of its closure in early 2001, the Sunshine was producing at a rate of over three million ounces of silver per year at an average grade of approximately twenty ounces per ton. The prior operator last estimated the mine reserves at 26.75 million ounces of silver, 10.36 million pounds of copper and 7.05 million pounds of lead (or approximately 28.85 million ounces of silver-equivalent), as well as an additional resource of 159.66 million ounces of silver.

Folklore & Mass Culture

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.

The Lone Ranger of radio serials, comic strips, and some TV programs leaves a silver bullet as a calling card.

Characteristics

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, though it was used in the electromagnets used for enriching uranium during World War II (mainly because of the wartime shortage of copper).

1s2
2s2 2p6
3s2 3p6 3d10
4s2 4p6 4d10
5s1

Pure silver has the highest thermal conductivity, whitest color, the highest optical reflectivity, although aluminum slightly outdoes it in parts of the visible spectrum, and is a poor reflector of ultraviolet light).  Silver also has 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, AgNO3); a few +2 (for example, silver (II) fluoride, AgF2) and +3 compounds (for example, silver (III) persulfate; Ag2(SO5)3) are also known.

Occurrence

Silver is found in native form, combined with sulfur, arsenic, antimony, or chlorine and in various ores such as argentite (Ag2S) and horn silver (AgCl).   Another ore it is found in is pyrargyrite.  The principal sources of silver are copper, copper-nickel, gold, lead and lead-zinc ores obtained from Candada, Mexico (historically Batopilas), Peru, Australia and the United States.

This metal can also be produced during the electrolytic refining of copper and by application of the Parkes process on lead metal obtained from lead ores that contain small amounts of silver.  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.

Applications

A major use of silver is as a precious metal.  Sterling silver is 92.5 % silver, alloyed usually with copper.  Jewelry and silverware are traditionally made from this.  Silver is used in medals, denoting second place.  Many high end musical intruments are made with silver, which benefit from a higher tone quality.

The name of United Kingdom monetary unit 'Pound' originally had the value of one troy pound of sterling silver.  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 largest single end use of silver is photography.  Sliver nitrate (AgNO3) is light sensitive and used to make photographic films and papers. Silver iodide (AgI) is used to seed clouds to produce rain.

Some electrical and electronic products use silver for its superior conductivity, even when tarnished.  For example, printed circuits are made using silver paints,   and computer keyboards use silver electrical contacts.  Silver cadmium oxide is used in high voltage contacts because it can minimize arcing.  Silver is also used to make sp;der and brazing alloys, electrical contacts, and high capacity silver-zinc and silver-cadmium batteries.  Silver in a thin layer of on top of a bearing material can provide a significant increase in galling resistance and reduce wear under heavy load, particularly against steel.

Mirrors which need superior reflectivity for visible light are made with silver as the reflecting material in a process called silvering, though common mirrors are backed with aluminum.  Using a process called sputtering, silver (and sometimes gold) can be applied to glass at various thicknesses, allowing different amounts of light to penetrate.   This is most often seen in architectural glass and tinted windows on vehicles.

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 thinkness.  Such a membrane could be used to filter pure oxygen from air.

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 antobiotics.   Silver nitrate solution 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.

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.  A company called Thomson Research Associates has began treating products with Ultra Fresh, an anti-microbial technology involving "proprietary nano-technology to produce the ultra-fine silver particles essential to ease of application and long-term protection".

The malleability, non-toxicity and beauty of silver make it useful in dental alloys for fittings and fillings.

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 dragees and the decoration of sugar-coated flour confectionery.  In Australia, it is banned as a food additive.

Price

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 Comstack Lode in Virginia City, Nevada.  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 $49.45 per troy ounce.  By December 2001 the price had fallen to $4.15 per ounce, and in May 2006 it had risen back as high as $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 $15.21 per ounce to a June low of $9.60 per ounce before rising back above $12 per ounce by August.

Compounds

Isotopes

Naturally occurring silver is composed of the two stable isotopes 107Ag and 109Ag with 107Ag being the more abundant (51.839% natural abundance.  Thirty-six 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-lives that are less than an hour and the majority of these have half-lives that are less than 3 minutes.  This element 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 92.94978 u  (93Ag) to 129.95045 u (130Ag).  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 palladium/silver 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.

atom.gif (700 bytes)

Isotope  
Atomic Mass
 
Half-Life
93Ag 92.94978 ~5 ms
94Ag 93.94278 37 ms
95Ag 94.93548 1.74 seconds
96Ag 95.93068 4.45 seconds
97Ag 96.92397 25.3 seconds
98Ag 97.92157 47.5 seconds
99Ag 98.91760 124 seconds
100Ag 99.91610 2.01 minutes
101Ag 100.91280 11.1 minutes
102Ag 101.91169 12.9 minutes
103Ag 102.908973 65.7 minutes
104Ag 103.908629 69.2 minutes
105Ag 104.906529 41.29 days
106Ag 105.906669 23.96 minutes
107Ag 106.905097 Stable
108Ag 107.905956 2.37 minutes
109Ag 108.904752 Stable
110Ag 109.906107 24.6 seconds
111Ag 110.905291 7.45 days
112Ag 111.907005 3.130 hours
113Ag 112.906567 5.37 hours
114Ag 113.908804 4.6 seconds
115Ag 114.90876 20.0 minutes
116Ag 115.91136 2.68 minutes
117Ag 116.91168 73.6 seconds
118Ag 117.91458 3.76 seconds
119Ag 118.91567 6.0 seconds
120Ag 119.91879 1.23 seconds
121Ag 120.91985 0.79 seconds
122Ag 121.92353 0.529 seconds
123Ag 122.92490 0.300 seconds
124Ag 123.92864 172 ms
125Ag 124.93043 166 ms
126Ag 125.93450 107 ms
127Ag 126.93677 79 ms
128Ag 127.94117 58 ms
129Ag 128.94369 44 ms
130Ag 129.95045 ~50 ms

Precautions

40px-Skull_and_crossbones.svg.jpg (1420 bytes) 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 kill 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 different theories exist.  One of these is a process generally known for heavy metals called the oligodynamic effects, which goes a long way explaining the effect on microbial lifeforms but does not explain certain antiviral functions.

atom.gif (700 bytes)

Silver Data
 

Atomic Structure

  • Atomic Radius: 1.75
  • Atomic Volume: 10.3cm3/mol
  • Covalent Radius: 1.34
  • Cross Section (Thermal Neutron Capture) Barns: 63.6
  • Crystal Structure: Cubic face centered
  • Electron Configuration:
    1s2 2s2p6 3s2p6d10 4s2p6d10 5s1
  • Electrons per Energy Level: 2, 8, 18, 18, 1
  • Ionic Radius: 1.26
  • Filling Orbital: 4d10
  • Number of Electrons (with no charge): 47
  • Number of Neutrons (most common/stable nuclide): 61
  • Number of Protons: 47
  • Oxidation States: 1
  • Valence Electrons: 4d10 5s1

Chemical Properties

  • Electrochemical Equivalent: 4.0246 g/amp-hr
  • Electron Work Function: 4.26eV
  • Electronegativity: 1.93 (Pauling); 1.42 (Allrod Rochow)
  • Heat of Fusion: 11.3 kJ/mol
  • Incompatibilities:
    Acetylene, ammonia, hydrogen peroxide, bromoazide, chlorine trifluoride, ethyleneimine, oxalic acid, tartaric acid
  • Ionization Potential
    • First: 7.576
    • Second: 21.49
    • Third: 34.83
  • Valence Electron Potential (-eV): 11.4

Physical Properties

  • Atomic Mass Average: 107.8682
  • Boiling Point: 2436K, 2163C, 3925F
  • Coefficient of Lineal Thermal Expansion/K-1: 19.2E-6
  • Conductivity
    Electrical: 0.63 106/cm
    Thermal: 4.29 W/cmK
  • Density: 10.5 g/cm3 @ 300K
  • Description:
    Very soft and malleable silver metal. Appearance and odor vary depending upon specific compound.
  • Elastic Modulus:
    • Bulk: 103.6/GPa
    • Rigidity: 30.3/GPa
    • Youngs: 82.7/GPa
  • Enthalpy of Atomization: 284.5 kJ/mole @ 25C
  • Enthalpy of Fusion: 11.3 kJ/mole
  • Enthalpy of Vaporization: 255.1 kJ/mole
  • Flammablity Class: Non-combustible solid (except as dust)
  • Freezing Point: see melting point
  • Hardness Scale
    • Brinell: 24.5 MN m-2
    • Mohs: 2.5
    • Vickers: 251 MN m-2
  • Heat of Vaporization: 250.58 kJ/mol
  • Melting Point: 1234K, 961C, 1762F
  • Molar Volume: 10.27 cm3/mole
  • Optical Reflectivity: 97%
  • Physical State (at 20C & 1atm): Solid
  • Specific Heat: 0.235 J/gK
  • Vapor Pressure: 0.342 Pa @ 961C

Regulatory / Health

  • CAS Number
    • 7440-22-4
  • RTECS: VW3500000
  • NFPA 704
    • Health: 1
    • Fire: 2
    • Reactivity:
    • Special Hazard:
  • 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
  • Routes of Exposure: Inhalation; Ingestion; Skin and/or eye contact
  • Target Organs: Nasal septum, skin, eyes
  • Levels In Humans:
    Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
    • Blood/mg dm-3: <0.003
    • Bone/p.p.m: 0.01-0.44
    • Liver/p.p.m: 0.005-0.25
    • Muscle/p.p.m: 0.009-0.28
    • Daily Dietary Intake: 0.0014-0.08 mg
    • Total Mass In Avg. 70kg human: 2 mg

Who / Where / When / How

  • Discoverer: Known to ancient civilization
  • Discovery Location: Unknown
  • Discovery Year: Unknown
  • Name Origin:
    Latin argentum (silver). Silver from Anglo-Saxon seolfor for silver.
  • Abundance:
    • Earth's Crust/p.p.m.: 0.07
    • Seawater/p.p.m.:
      • Atlantic Suface: N/A
      • Atlantic Deep: N/A
      • Pacific Surface: 0.0000001
      • Pacific Deep: 0.0000024
    • Atmosphere/p.p.m.: N/A
    • Sun (Relative to H=1E12): 7.1
  • Sources:
    Found in ores called argentite (AgS), light ruby silver (Ag3AsS3), dark ruby silver (Ag3SbS3) and brittle silver. Silver is often obtained as a by-product of refining other metals like copper and gold. World wide production is around 9950 tons per year. Primary mining areas are Mexico, Bolivia, Honduras, Canada, USA.
  • Uses:
    Used in alloys for jewelry, in many compounds, photographic film and paper electronics, mirrors and batteries.

Ionization Energy (eV): 7.576 eV
Estimated Crustal Abundance: 7.510-2 milligrams per kilogram
Estimated Oceanic Abundance:
410-5 milligrams per liter

Transition Metals
Group 3
(IIIB)
4
(IVB)
5
(VB)
6
(VIB)
7
(VIIB)
8
(VIIIB)
9
(VIIIB)
10 (VIIIB) 11
(IB)
12
(IIB)
Period 4 21
Sc
44.95
22
Ti
47.86
23
V
50.94
24
Cr
51.99
25
Mn
54.93
26
Fe
55.84
27
Co
58.93
28
Ni
58.69
29
Cu
63.54
30
Zn
65.39
Period 5 39
Y
88.90
40
Zr
91.22
41
Nb
92.90
42
Mo
95.94
43
Tc
98.00
44
Ru
101.0
45
Rh
102.9
46
Pd
106.4
47
Ag
107.8
48
Cd
112.4
Period 6 57
La
138.9
72
Hf
178.4
73
Ta
180.9
74
W
183.8
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.0
79
Au
196.9
80
Hg
200.5
Period 7 89
Ac
227.0
104
Rf
261.0
105
Db
262.0
106
Sg
266.0
107
Bh
264.0
108
Hs
269.0
109
Mt
268.0
110
Ds
269.0
111
Rg
272.0
112
Uub
277.0