Gold

Gold (IPA: /ˈgəʊld/) is a highly sought-after precious metal that for many centuries has been used as money, a store of value and in jewellery. more...

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The metal occurs as nuggets or grains in rocks and in alluvial deposits and is one of the coinage metals. It is a soft, shiny, yellow, dense, malleable, and ductile (trivalent and univalent) transition metal. Modern industrial uses include dentistry and electronics. Gold forms the basis for a monetary standard used by the International Monetary Fund (IMF) and the Bank for International Settlements (BIS). Its ISO currency code is XAU.

Gold is a chemical element in the periodic table with the symbol Au (from the Latin aurum) and atomic number 79. The adjective auric refers to something made of gold. Gold does not react with most chemicals but is attacked by chlorine, fluorine, aqua regia and cyanide. Gold dissolves in mercury. In particular, gold is insoluble in nitric acid, which will dissolve most other metals. Nitric acid has long been used to confirm the presence of gold in items.

Characteristics

Gold is a metallic element with a characteristic yellow color, but can also be black or ruby when finely divided, while colloidal solutions are intensely colored and often purple. These colors are the result of gold's plasmon frequency lying in the visible range, which causes red and yellow light to be reflected, and blue light to be absorbed. Only silver colloids exhibit the same interactions with light, albeit at a shorter frequency, making silver colloids yellow in color.

It is the most malleable and ductile metal known; a single gram can be beaten into a sheet of one square meter, or an ounce into 300 square feet. Gold readily forms alloys with many other metals. These alloys can be produced to increase the hardness or to create exotic colors. Adding copper yields a redder metal, iron blue, aluminium purple, platinum metals white, and natural bismuth together with silver alloys produce black. Native gold contains usually eight to ten percent silver, but often much more — alloys with a silver content over 20% are called electrum. As the amount of silver increases, the color becomes whiter and the specific gravity becomes lower.

Gold is a great conductor of heat and electricity, and is not affected by air and most reagents. Heat, moisture, oxygen, and most corrosive agents have very little chemical effect on gold, making it well-suited for use in coins and jewelry; conversely, halogens will chemically alter gold, and aqua regia dissolves it.

Common oxidation states of gold include +1 (gold(I) or aurous compounds) and +3 (gold(III) or auric compounds). Gold ions in solution are readily reduced and precipitated out as gold metal by adding any other metal as the reducing agent. The added metal is oxidized and dissolves allowing the gold to be displaced from solution and be recovered as a solid precipitate.

Read more at Wikipedia.org