Gold
Symbol: Au
Atomic Number: 79
Atomic Mass: 196.96655 amu (atomic mass units)
Melting Point: 1064.43 C (1337.5801 K, 1947.9741 F)
Boiling Point: 2807.0 C (3080.15 K, 5084.6 F)
Number of Protons: 79
Number of Electrons: 79
Number of Neutrons: 118
Classification: Metal (coinage metal)
Crystal Structure: Cubic
Density @ 293 K: 19.32 grams per cubic centimeter
Color: Gold
The element gold has been known and valued by man for thousands of years. In addition to references to the metal in the Old Testament of the Bible, Egyptian writings dated at 2600 BCE also mention gold. The word gold is of Anglo-Saxon origin and the symbol “Au” derives from the Latin name for the element “aurum”.
Gold is one of the most malleable and ductile of all metals. It is possible to beat a single ounce of the metal to form a sheet with an area of 300 square feet. Very thin sheets of gold are known as gold leaf. It is possible to beat gold into a sheet as thin as 0.000127 millimeters, this so thin that it is possible to read text through it. The metal reacts with very few chemical reagents. One part nitric acid with three parts hydrochloric acid is called aqua regia because it can dissolve gold and gold is sometimes called “the king of metals”.
Most gold used to make jewelry consists of an alloy of gold and other metals such as silver, copper or platinum. Alloying of gold to other metals hardens the gold. The purity of gold is measured in carats. Twenty-four carat gold is pure gold. Eighteen-carat gold contains eighteen parts gold and six parts other metal.
There is only one naturally occurring isotope of gold, which is the stable isotope gold-137. Many unstable isotopes of gold with mass numbers ranging from 171 to 205 have been identified.
Gold exists as a free metal in nature. It is also found associated with other minerals such as quartz. Two thirds of the world’s production of gold comes from the mines of South Africa. In the United States most of the gold produced comes from deposits in South Dakota and Nevada. One ton of seawater contains one milligram of gold. As yet extraction processes to obtain gold from seawater are more expensive than the value of the gold extracted
Besides the manufacturing of jewelry, gold has a number of applications.
* People working in the arts and crafts use gold leaf for gilding.
* Gold resists tarnishing on exposure to air. In addition, it is a good conductor of electricity. These properties allow gold’s usage in making electrical contacts and printed circuit boards.
* Gold reflects infrared radiation. This ability makes it invaluable for protecting spacecraft as well as skyscrapers from heat.
* Infrared sensitive telescopes incorporate mirrors coated with gold.
* A fine coating of gold atoms applied to biological samples makes them visible in electron microscopy.
* The isotope gold-198 has a half-life of 2.96517 days and decays by beta decay. Doctors use this isotope to treat some forms of cancer.
* A number of gold compounds are effective drugs for the treatment of some autoimmune diseases such as rheumatoid arthritis and Lupus erythematosus. These include gold sodium thiosulfate, sodium aurothiomalate, aurothioglucose and Auranofin.
* Chlorauric acid (HAuCl4) preserves and tones photographic images. It replaces the silver atoms present in a photographic image with gold atoms.
The value man places on gold leads to it being the basis for many currencies. It is the most watched commodity on the world’s stock exchanges. If something is described as the gold standard then it is the best available.
Reference sources:
Medical uses of gold compounds Past present and future Simon P Fricker
Los Alamos National Laboratory’s Chemical Division Periodic Table of Elements
National Nuclear Data Center
Web Elements
