silver

From Wikipedia, the free encyclopedia Jump to: navigation, search This article is about the chemical element. For the color, see Silver (color). For other uses, see Silver (disambiguation). 47 palladium ← silver → cadmium Cu ↑ Ag ↓ Au Periodic Table - Extended Periodic Table General Name, Symbol, Number silver, Ag, 47 Element category transition metals Group, Period, Block 11, 5, d Appearance lustrous white metal Standard atomic weight 107.8682(2)  g·mol−1 Electron configuration [Kr] 4d10 5s1 Electrons per shell 2, 8, 18, 18, 1 Physical properties Color 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 250.58  kJ·mol−1 Specific heat capacity (25 °C) 25.350  J·mol−1·K−1 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, 2, 3 (amphoteric oxide) Electronegativity 1.93 (Pauling scale) Ionization energies 1st: 731.0 kJ/mol 2nd: 2070 kJ/mol 3rd: 3361 kJ/mol Atomic radius 144 pm Covalent radius 145±5 pm Van der Waals radius 172 pm Miscellaneous Magnetic ordering diamagnetic Electrical resistivity (20 °C) 15.87 n Ω·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 Most-stable isotopes 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 - 106mAg syn 8.28 d ε - 106Pd γ 0.511, 0.717, 1.045, 0.450 - 107Ag 51.839% 107Ag is stable with 60 neutrons 108mAg syn 418 y ε - 108Pd IT 0.109 108Ag γ 0.433, 0.614, 0.722 - 109Ag 48.161% 109Ag is stable with 62 neutrons 111Ag syn 7.45 d β− 1.036, 0.694 111Cd γ 0.342 - References Silver is a chemical element with the chemical symbol Ag (Latin: argentum, from the Ancient Greek: ἀργήεντος - argēentos, gen. of ἀργήεις - argēeis, "white, shining" ) and atomic number 47. A soft, white, lustrous transition metal, it has the highest electrical conductivity of any element and the highest thermal conductivity of any metal. The metal occurs naturally in its pure, free form (native silver), as an alloy with gold (electrum) and other metals, and in minerals such as argentite and chlorargyrite. Most silver is produced as a by-product of copper, gold, lead, and zinc refining. Silver has been known since ancient times and has long been valued as a precious metal, used to make ornaments, jewelry, high-value tableware, utensils (hence the term silverware), and currency coins. Today, silver metal is used in electrical contacts and conductors, in mirrors and in catalysis of chemical reactions. Its compounds are used in photographic film and dilute solutions of silver nitrate and other silver compounds are used as disinfectants. Although the antimicrobial uses of silver have largely been supplanted by the use of antibiotics, further research into its clinical potential is in progress. Contents [hide] 1 Characteristics 2 Isotopes 3 Silver compounds 4 Applications 4.1 Precious metal 4.1.1 Currency 4.1.2 Jewellery and silverware 4.2 Dentistry 4.3 Photography and electronics 4.4 Solder and brazing 4.5 Mirrors and optics 4.6 Nuclear reactors 4.7 Catalyst 4.8 Medicine 4.8.1 Medication 4.9 Food 4.10 Clothing 5 History 6 Occurrence and extraction 7 Price 8 Precautions 9 See also 10 References 11 External links [edit] Characteristics Silver 100oz bullion bar a silver crystal, electrolytic refined with visible dendritic structures. Silver is a very ductile and malleable (slightly harder than gold) monovalent 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 have prevented it from being widely used in place of copper for electrical purposes, though 13540 tons were used in the electromagnets used for enriching uranium during World War II (mainly because of the wartime shortage of copper).[1][2] Another notable exception is in high-end audio cables.[3] Among metals, pure silver has the highest thermal conductivity[4] (the non-metal diamond and superfluid helium II are higher), the whitest color, and the highest optical reflectivity[5] (although aluminium slightly outdoes it in parts of the visible spectrum, and it 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 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 to form a black layer of silver sulfide which can be cleaned off with dilute hydrochloric acid.[6] The most common oxidation state of silver is +1 (for example, silver nitrate: AgNO3); in addition, +2 compounds (for example, silver(II) fluoride: AgF2) and +3 compounds (for example, potassium tetrafluoroargentate: K[AgF4]) are known. [edit] Isotopes Main article: isotopes of silver Naturally occurring silver is composed of two stable isotopes, 107Ag and 109Ag, with 107Ag being the most abundant (51.839% natural abundance). Silver's standard atomic mass is 107.8682(2) u. Twenty-eight radioisotopes have been characterized, 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. This element has numerous meta states, the most stable being 108mAg (t* 418 years), 110mAg (t* 249.79 days) and 106mAg (t* 8.28 days). 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. 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 palladium-to-silver ratio to yield measurable variations in 107Ag abundance. Radiogenic 107Ag was first discovered in the Santa Clara meteorite in 1978.[7] The discoverers suggest that the coalescence and differentiation of iron-cored small planets may have occurred 10 million years after a nucleosynthetic event. 107Pd–107Ag correlations observed in bodies that have clearly been melted since the accretion of the solar system must reflect the presence of unstable nuclides in the early solar system.[8]