Gold Periodic Table Facts
Gold (Au), chemical element, the yellow precious metal of Group 11 or 1B, and period 6 of the periodic table uses widely from ancient history in jewelry or coinage production. The name gold is derived from the old English word geolu means yellow and from the Latin word aurum. Copper, silver, and gold constitute the family of the coinage of currency metals and occurs in nature in a native form with very similar chemical and physical properties in chemistry. The chemically unreactive, extremely malleable, ductile, high density (19.32 gm cm-3), attractive golden-yellow color, and bright metal gold found in nature’s very pure form. The purity of metal expressed in carats, pure gold is 24 carat and common alloyed form with copper is 22 carat.
The good conductor of specific heat and electricity gold has the chemical symbol Au, atomic number 79, atomic weight 196.967, melting point 1064 °C, boiling point 2808 °C, valence shell electron configuration [Kr] 4f14 5d10 6s1, and common oxidation number state +3. The metal from fcc crystal lattice in the solid form is known for its characteristic color. In learning chemistry, the characteristic golden yellow color of gold arises from the absorption in the UV and blue regions of the electromagnetic spectrum corresponding to the excitation of electrons from filled d-band to s-p conduction band.
Occurrence and Extraction of Gold
Native gold occurs in nature in two forms, reef-Au (deposit or dispersed fine particles in quartz veins in deep mines), alluvial-Au (primary deposit by geological action and redeposited in alluvial sands gravel as fine grains). The combined form of gold is found in a few minerals like calaverite, AuTe2, and sylvanite, (Ag, Au)Te2. It is also present in sea-water to the extent of 10-3 ppm but no extraction methods were developed to gain the metal from sea-water. China (383.2 tonnes), Russia (329.5), Australia (325.1), United States (200.2), Canada (182.9), Peru (143.3), Ghana (142.4), South Africa (188.2), Mexico (118.4), Brazil (106.9) is the top 10 commercial gold producer countries in tonnes of the world in 2019 report.
Gold is extracted mainly by the cyanide and amalgamation process. In the cyanide process, the finely powdered rocks were ignited with dilute sodium cyanide (NaCN) solution and lime in presence of air for oxidation. The solution filtered and Au deposited from the filtrate by zinc shavings. Zinc is dissolved out by dilute sulfuric acid (H2SO4) and the dried residue is melted with borax. The crude gold contains copper, silver, and lead. Lead is removed by cupellation, copper is removed by oxidative fusion of borax and silver may be removed by boiling with concentrated sulfuric acid. The amalgamation electrolysis process was also used to separate native gold from alluvial sand and gravel deposits. The finely crusted rocks amalgamated with mercury with the stream of water over copper plates. The amalgam is scared and mercury distilled out in iron retorts.
The chemically unreactive gold is the noblest transition metals of the periodic table. It does not attract by oxygen, sulfur, or readily react with halogens like fluorine, chlorine, bromine, and iodine molecule, it will be dissolved in cyanide solution in presence of hydrogen peroxide or aqua regia (a mixture of concentrated nitric acid and hydrochloric acid). The first ionization energy of silver in the noble element family is the lowest, the sum of the first and second ionization energy of copper is the lowest, the sum of the first second, and third ionization energy of gold is lowest. The fact suggests the common oxidation state of Cu, Ag, and Au. For gold, atomization, ionization, hydration energy favors the formation of Au(III) in aqueous solutions.
Although the small size but no simple monovalent cation of gold can exist, most of the compounds are formed by covalent bonding or by the form of complexes. The simple compound of gold (I) is restricted to chlorine, bromine, and iodine only. The oxide, Au2O obtained by dehydrating AuOH with alkali metals and sulfur dioxide. AuCl and AuBr are prepared by controlled thermal decomposition of respective halide but AuI prepared by heating the metal with iodine solution or adding iodine solution to AuCl3 solution. +2 oxidation state is unfavorable for gold in comparison to Au(I) and Au(II) and few complexes of AU(II) have been claimed. For example, tetra n-butylammonium salt of the bis (maleonitriledithiolato) aurate(II).
Au(III) is the most common oxidation state of gold offering a number of chemical compounds and complexes with the molecular formula Au2O3, Au(OH)3, AuF3, AuCl3, AuBr3, Au2S3, etc. Au2S3 is prepared by passing H2S over dry LiAuCl4, 2H2O at 10 °C. The lithium chloride is separated by extracting with alcohol and dried at 70 °C. The orange crystalline solid of gold (III) fluoride is made by the action of fluorine on Au2Cl6 at 300 °C. AuF7 and AuF5 are examples of gold compounds that show a higher than +3 oxidation state formed by the covalent chemical bonding.
Uses of Gold
Gold and its compounds are extensively used in medicine in old age Ayurveda as well as in modern Allopathy, particularly for the treatment of arthritis. Because of its bright color and chemical reactivity, it was the first metal that attracts the human eye to prepare coins, different types of craft jewelry, and decorative objects. Due to the unique qualities of gold, the materials are universally accepted in goods and services in the form of coins or bullion to affect the currency of the world. The modern currency is paper-based currency but gold paly a key role dominate the currency of the country because it is accepted by all nations as a medium of international payments technique. A purple powder containing colloidal gold absorbed on the hydrated tin (II) oxide, used in making ruby glass. The purple powder is prepared by reducing Au(II) chloride with SnCl2.
The pure gold is 24 carat (24 parts of Au by weight and 2 parts of other metals in weight) alloyed with other metals to increasing softness and brightness to easy use for jewelry, goldware, and coins making. The alloyed metals are silver, copper, and zinc, platinum, and palladium. The silver alloyed gold is used to make coins or goldware and the platinum or palladium alloyed metal commonly used for making craft jewelry. Due to electrical conductivity, thermal conductivity, and unreactive properties, we use a large amount of gold for industrial purposes in electric or electronics engineering in making terminals, plating contacts, printed circuits, and semiconductors.