Silver Periodic Table Facts
Silver (Ag), atomic number 47, the shiny white, lustrous metal of Group 11 or IB in periodic table chemical element uses from the ancient age to jewelry, coinage (decorative beauty), and electrical conductivity. The name silver comes from Assyrian serpu or Gothic silbur meaning white and from Latin name, Argentum means shiny white (Greek latter Argos). The noble metal, silver form an FCC crystal lattice structure with characteristic silvery-white colour. Although the atomic states of copper, silver, and gold (noble metal family) contain ns1 (n-1)d10 outer electron configuration or filled d-subshell but they considered transition elements because in +2 and +3 oxidation number or state of chemical element posses incompletely filled d-orbital.
Chemically, silver metal is quite unreactive element with chemical symbol = Ag, atomic weight = 107.868, melting point = 961.8 °C, boiling point = 2162 °C, and electrical resistivity = 1.67 ohm-cm. The learning chemistry, silver dissolved in water to the extent of 0.07 mg liter-1 in presence of dissolved oxygen and attacked by atmospheric sulfur compounds, mainly hydrogen sulfide (H2S).
Occurrence and Production
The relative occurrence of metal in earth crust = 0.08 ppm while that of gold = 0.004 ppm, widely distributed in nature as sulfide ore like silver glance or argentite (Ag2S). Horn silver (AgCl) is found in some minerals in Chile and New South Wales formed by the action of saltwater. Silver is now largely discovered as a byproduct in the extraction of copper and lead and produces by counties, United States, Canada, Peru, Mexico, Bolivia, and New South Wales. In India, it is obtained from Kolar gold mines produces from the smelting of Zawar lead ores.
Mostly silver obtained as a byproduct of the extraction of copper, lead, and zinc by collecting anode slime or mud. The anode slime or mud is heated with dilute sulfuric acid in a stream of air to dissolve some metals. The remaining anode slug heated with lime and silica to remove most of the base metal as a slug. Finally, silver-containing materials are dissolved in dilute nitric acid and the AgNO3 solution electrolysis to get a pure form of metal at the cathode. Silver is extracted from its important ores by leaching the finely powdered ore with dilute (0.4 percent) sodium cyanide solution and the sludge is agitated well with air. The Na2S oxidized by aeration, otherwise, it would tend to reverse reaction. The sludge is removed by filtration formula and the filtrate silver is precipitated by chemical zinc or aluminum. The precipitate is washed and melted with a flux of nitrate to remove the excess of zinc.
The physical and chemical properties of silver are similar to the two vertical neighbor copper and gold of the periodic table. The higher effective nuclear charge or ionic potential and large shielding electron suggest that the covalent bonding of silver and gold compounds are stable and aqueous ion, Ag+, and Ag+2 are a strongly oxidizing agent. The first ionization energy is lowest for silver, the sum of the first and second ionization is lowest for copper, and the sum of first, second, and third ionization energy is lowest for gold atom. The fact reflects that silver chemistry predominant in the +1 oxidation state but copper and gold chemistry predominates in the +2 and +3 oxidation state. The facts also describe by hydration energy, the hydration energy of copper (II) ion is much higher than the copper (I) ion which overcome the second ionization of Cu in an aqueous medium. Due to higher ionic radii of Ag, the hydration energy cannot stabilize Ag (II) ion over Ag (I). For gold atoms, atomization, ionization, and hydration energy favor the formation of Au (III) in an aqueous medium but Au (III) ion is not known such.
The most common oxidation state which offering the oxides, sulfide, halides, and a number of oxoacids salts of silver is +1. The salts are primarily ionic and quite soluble in water but Ag2SO4 and CH3COOAg are sparingly soluble in water. The halide (except AgF) are formed by covalent chemical bonding. Silver (II) compounds are obtained by direct oxidation or disproportionate of chemical element which is extremely unfavorable due to low heat of hydration of Ag+2 ion. AgF2 is the only known silver halide obtained by the action of fluorine on AgF or Ag at 250 °C temperature uses as a fluorinating agent. A black oxide like AgO is formed by oxidation of Ag2O ozone molecule or by electrolysis 2M AgNO3 solution. Compounds of Ag(III) are very few, Ag2O3, Ag(OH)4–, KAgF4 or Cs2KAgF6 are the common examples of the +3 oxidation state of silver.
Uses of Silver
Silver and its compounds are widely used in photography, in silvering mirrors or plate, in silverware, jewelry, dentistry, and coins, and in high capacity electrical cells (Ag-Zn, Ag-Cd). Copper serves to increases the hardness of alloy to improve the wearing qualities. The photographic light sensitivity plate consists of an emulsion of fine-grain silver halides like bromide, chloride, or iodide (diameter <1 μm) on a transparent medium like glass or celluloid. The halide is usually AgBr with some amount of AgCl and organic dyes but AgI used in very fast films. Organic dyes act as a photosensitizer to help light absorption over the entire visible band. Silver plating in chemistry is done at the cathode of the electrolytic cell, a piece of pure Ag element acts as anode with the electrolytic solution sodium dicyanoargentate, Na[Ag(CN)2].
Detection and Estimation of Silver
Silver salts in aqueous solution produce a curdy white precipitate of AgCl with chlorine ion, the precipitate insoluble in nitric acid but readily dissolved in aqueous ammonia. Silver ion also forms a red precipice (Ag2CrO4) with potassium dichromate solution which is insoluble in acetic acid. All the silver compounds produce a lustrous white malleable bed on heating with sodium carbonate on charcoal, the bead may be dissolved in nitric acid and tested with hydrogen chloride (HCl).
In learning chemistry or chemical science, silver may be estimated gravimetrically as chloride or by electrodeposition (coulometer), volumetrically, it is determined by titration with a standard solution of sodium chloride ammonium thiocyanate. In Mohrs’s method, a known volume of standard sodium chloride solution triturated with AgNO3 solution using potassium chromate as an indicator. In Volhard’s method, the silver nitrate (AgNO3) is triturated by standard potassium or ammonium thiocyanate using ferric alum as an indicator, the Ag+ ion forms a white precipitate of AgSCN but when the concentration falls below the solubility, the blood-red color of thiocyanate ions produce with ferric ion.