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Au. Element with atomic number 79. Group 11 transition element in the periodic table. Atomic weight 196.96655(2). There is a stable isotope with mass number 197 (100%) and radioactive isotopes ranging from 169 to 205. The element symbol is the first two letters of the Latin name aurum (meaning yellow). Udagawa Yoan transliterated this as aurum in his book Shamitsu Kaisou, published in 1837.
Gold is the metal that has been used by humans since ancient times, and gold tools have been found in Egyptian ruins dating back to 5000 BC. The world's largest gold nugget was discovered in Victoria, Australia in 1869, weighing 2,520 ounces (about 71 kg), yielding 2,280 ounces of pure gold. In Japan, the Shoku Nihongi records that gold was first produced in Mutsu Province in 749, the 21st year of the Tenpyo era under Emperor Shomu. Historically, the Sado, Konomai, and Kushikino gold mines are well known, but as of 2007, the only operating gold mine in Japan is the Hishikari Mine (Kagoshima Prefecture), where a gold vein was discovered in 1981. The gold content of the ore at this mine is very high, averaging 40 g (40 ppm) per ton, which is about 10 times the world average, and the mine produces 7 to 8 tonnes of gold per year. In addition, in 2005, there was approximately 150 t of new gold produced as a by-product of copper, zinc, and lead ore refining, and 30 t of recycled gold from discarded personal computers, mobile phones, and plating waste fluids. Most gold exists as native gold, produced as gold dust with the weathering of the quartz host rock. Native gold contains silver as an impurity. It is also found in copper ore, lead ore, and pyrite. Its abundance in the earth's crust is 0.003 ppm. Of the estimated total world reserves of 90,000 t, 40% is found in South Africa, followed by Australia at 7%, and China and Peru at just under 5% each. In addition to the mercury amalgamation method, in which the ore is extracted by amalgamating it with mercury, and the Merrill Crowe method, in which gold is extracted as a cyano complex ion by treatment with sodium cyanide (cyanide method) and then zinc powder is added to precipitate gold, a method in which the cyano complex ion from the cyanide method is adsorbed and separated on activated carbon (carbon-in-pulp method) and solvent extraction have become popular since the 1970s. It is refined by electrolysis. It is a metal with a beautiful golden luster. Its crystals form a face-centered cubic lattice. Its density is 19.32 g cm -3 (20 °C). Its melting point is 1064.43 °C, its boiling point 2810 °C. Its molar heat capacity at constant pressure is 25.38 JK -1 mol -1 (25 °C). Its linear expansion coefficient is 0.1424 × 10 -4 K -1 (0 to 100 °C). Thermal conductivity: 315 W m -1 K -1 (27 °C). Heat of fusion: 12.7 kJ mol -1 (1063 °C). Heat of vaporization: 310.5 kJ mol -1 (2660 °C). Electrical resistivity: 2.35 x 10-6 Ω cm (20 °C). Standard electrode potential (Au3 + /Au): 1.52 V. First ionization energy: 889.9 kJ mol -1 (9.225 eV). It is a good thermal conductor, 73% as good as silver, and also a good electrical conductor, third only to silver and copper, with an electrical resistivity 1.48 times that of silver. It is the most ductile of all metals. Hardness: 2.5-3. It is very stable chemically. It is insoluble in acid by itself. It dissolves in aqua regia to form HAuCl4 . At high temperatures it does not react with oxygen or sulfur, but will combine directly with bromine and chlorine. Its normal oxidation number is 1 to 3. Pure gold is considered to be 24 carats, and when it contains 50% gold it is expressed as 12 carats. In Japan, the largest use in 2005 was for electronic component materials (just under 50%), including IC packages for personal computers and mobile phones, printed circuit boards, lead frames, bonding wire, connectors, and electrical equipment for automobiles. Next was gold bullion for assets (just under 25%), jewelry (10%), and dental and medical alloys (5%). [CAS 7440-57-5][See alternative terms]Gold compounds Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition |
