Group 11 element
From Wikipedia, the free encyclopedia
| Group | 11 |
|---|---|
| Period | |
| 4 | 29 Cu |
| 5 | 47 Ag |
| 6 | 79 Au |
| 7 | 111 Rg |
A Group 11 element is one in the series of elements in group 11 (IUPAC style) in the periodic table, consisting of transition metals which are the traditional coinage metals of copper (Cu), silver (Ag), and gold (Au). They are also known as the "noble metals." The name "coinage metals" is not recognized by the International Union of Pure and Applied Chemistry (IUPAC), and can be somewhat misleading as further elements are added to the table. In addition, various nations have used probably dozens of metals (including stainless steel, lead, and zinc) in coins. The short-lived transactinide roentgenium (Rg) is also a member of Group 11.
| Explanation of right side periodic table slice: | Transition metals | atomic numbers in black are solids | solid borders are older than the Earth (Primordial elements) | dashed borders have no isotopes older than the earth |
They are all relatively inert, corrosion-resistant metals which have been used for minting coins, hence their name. Many metals form colored compounds, such as iron pyrite, and many metals have a colored sheen, but apart from caesium, which also has 1 6s-electron, similar to gold, only gold and copper are colored.
These metals, especially silver, have unusual properties that make them essential for industrial applications outside of their monetary or decorative value. They are all excellent conductors of electricity. The most conductive of all metals are silver, copper and gold in that order. Silver is also the most thermally conductive element, and the most light reflecting element. Silver also has the unusual property that the tarnish that forms on silver is still highly electrically conductive.
Copper is used extensively in electrical wiring and circuitry. Gold contacts are sometimes found in precision equipment for their ability to remain corrosion-free. Silver is used widely in mission-critical applications as electrical contacts, and is also used in photography (because silver nitrate reverts to metal on exposure to light), agriculture, medicine, audiophile and scientific applications.
Gold, silver, and copper are quite soft metals and so are easily damaged in daily use as coins. Precious metal may also be easily abraded and worn away through use. In their numismatic functions these metals must be alloyed with other metals to afford coins greater durability. The alloying with other metals makes the resulting coins harder, less likely to become deformed and more resistant to wear.
Gold coins: Gold coins are typically produced as either 90% gold (e.g. with pre-1933 US coins), or 22 carat (92%) gold (e.g. current collectible coins and Krugerrands), with copper and silver making up the remaining weight in each case. Bullion gold coins are being produced in 99.99% gold, e.g. Canadian Mapleleaf and, as of July 2006, the American Buffalo.
Silver coins: Silver coins are typically produced as either 90% silver - in the case of pre 1965 US minted coins (which were circulated in many countries), or sterling silver (92.5%) coins for pre-1967 British Commonwealth and other silver coinage, with copper making up the remaining weight in each case.
Copper coins: Copper coins are often of quite high purity, around 97%, and are usually alloyed with small amounts of zinc and tin.
The rise of fiat currency has caused the face value of coins to fall below the hard currency value of the historically used metals. This had led to most modern coins being made of base metals - Cupro-nickel (around 80:20, silver in color) is popular as are nickel-brass (copper (75), nickel (5) and zinc (20), gold in color), manganese-brass (copper, zinc, manganese, and nickel), bronze, or simple plated steel.
