1 Notable characteristics
Gold is a metallic element that exhibits a yellow color en masse but can be black, ruby, or purple when finely divided. It is the most malleable and ductile metal known. In fact, 1 gram can be beaten into a 1 meterē sheet, or 1 ounce into 300 feetē. A soft metal, gold is often alloyed with other metals to give it more strength.
Gold is also a good conductor of heat and electricity and is not affected by air and most reagents. It is quite chemically unalterable by heat, moisture, and most corrosive agents and therefore is well suited for its use in coin and jewelry.
The color of solid gold as well as of the intensely colored, often purple, colloidal solutions that can be made from it is caused by the fact that the plasmon frequency of this element lies in the visible range, which causes red and yellow light to be reflected and blue light to be absorbed. Native gold contains usually eight to ten per cent silver, but often much more. Natural alloys with a high silver content are called electrum. As the amount of silver increases, the color becomes whiter and the specific gravity lower.
Gold will alloy with many other metals, alloys with copper yield a redder metal, alloys with iron are green, aluminium alloys are purple, alloys with platinum metals produce white, natural bismuth with silver alloys produce black. Jewelry made with combinations of colored gold is sold in the western United States to the tourist trade as Black Hills gold.
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 the addition of virtually 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.
2 Applications
Pure gold is too soft for ordinary use and is hardened by alloying with silver and copper. Gold and its many alloys are most often used in jewelry, coinage and as a standard for monetary exchange in many countries. Because of its superior electrical conductivity and resistance to corrosion and other desirable combinations of physical and chemical properties, gold also emerged in the late 20th century as an essential industrial metal.
Other uses:
- Gold performs critical functions in computers, communications equipment, spacecraft, jet aircraft engines, and a host of other products.
- The high electrical conductivity and resistance to oxidation of gold has led to its widespread use as thin layers electroplated on the surface of electrical connectors to ensure a good, low-resistance connection.
- Like silver, gold can form a hard amalgam with mercury, and is sometimes used for dental fillings.
- Colloidal gold (gold nanoparticle s) is an intensely colored solution that is currently studied in many labs for medical, biological and other applications. It is also the form used as gold paint on ceramics prior to firing.
- Chlorauric acid is used in photography for toning the silver image.
- Disodium aurothiomalate is a treatment for rheumatoid arthritis (administered intramuscularly).
- The gold isotope Au-198, ( half-life: 2.7 days) is used in some cancer treatments and for treating other diseases.
- Gold is used as a coating enabling biological material to be viewed under a scanning electron microscope.
- Many competitions and honors, such as the Olympics and the Nobel Prize, award a gold medal to the winner (with silver to the second-place finisher, and bronze to the third.)
- Since it is a good reflector of both infrared and visible light, it is used for the protective coatings on many artificial satellites.
- Gold flake is used on and in some gourmet sweets and drinks. Having no reactivity it adds no taste but is taken as a delicacy.
