The Coinage Metals: Copper, Silver, and Gold
The “coinage metals”, copper, silver, and gold, have held great importance in societies throughout history, both symbolically and practically. For centuries, silver and gold have been worn by royalty to parade their wealth and power. On occasion, these metals were even used in art; during the height of the Byzantine Empire, artists would use gold leaf in mosaics and paintings of royalty as well as in renderings of religious figures, which further demonstrated the power of the individuals represented in these masterpieces.
On a more practical note, these metals are also an integral part of the United States' monetary system, hence the nickname of the "coinage metals".For a good part of the 20th century, the United States functioned on the "gold standard", which basically meant that the dollar was used as a paper representation of a certain amount of gold.Although this system has been discarded, gold and silver are still traded today.
Group 11 Metals
Copper, silver, and gold have been chosen as currency for so long because they are durable and they do not readily react with many other materials. They generally do not oxidize in air, unless it is particularly moist in copper's case. These metals also display high levels of the physical properties of metals; copper, silver, and gold are all particularly malleable, ductile and are also good conductors.
These metals use their d orbital in chemical bonding, just like other transition metals and so they exist in several oxidation states, which can be seen in the table listing several of the properties of the coinage metals. They can also form complex ions and demonstrate paramagnetism.
Table 1: Some properties of Copper, Silver, and Gold
The element copper is used in a variety of ways, including agriculturally, industrially and even in our own bodies. Small amounts of copper are vital to life. It is found in the several tissues and helps certain enzymes function. However, in larger doses, it becomes toxic; thus, copper is a popular component of many pesticides, usually CuSO4• 5 H2O. Copper sulfate is also used in batteries as well as electroplating. It is also popularly used in wiring and piping, since it is such a good conductor and is highly malleable.
Although copper is somewhat resistant to corrosion, in air with high levels of moisture, it does corrode but into a copper carbonate which incidentally protects the metal beneath it.
2 Cu(s) + H2O(g) + CO2(g) + O2 → Cu2(OH)2CO3(s)
Silver is also a very popular metal. Like gold, silver is a rare metal and holds great value and is also traded in similar markets. Silver is also a popular metal to make jewelry with because of both its rarity and malleability. For some time, silver was also used in dentistry, although it had to be mixed with mercury because it is not quite as malleable as gold. Silver is also a good conductor and is used in electroplating. It is also used in the manufacturing of batteries as well as a catalyst.
Silver also played a vital role in photography and consequently, medicine. The first camera-like apparatus was developed during the Middle Ages, but they had no way to make the captured images permanent. Then during the 19th century, the first permanent photos were developed using silver nitrate coated glass plates, which were used as negatives, and modern photography soon developed. However, this process is quickly becoming obsolete due to the emergence of digital photography.
The development of permanent photography catalyzed the development of modern medicine. As a result of permanent photography and the silver halides used in its development, William Conrad Roentgen was able to use radiation to create a picture of a person's skeleton, making it easier for doctors to diagnose their patients.
Even though coinage metals are known to be resistant to air oxidation, silver will tarnish due to the
2Ag(s) + S(g) → Ag2S (s)
Gold, like the other coinage metals, is popularly used. It is commonly used to make jewelry, and it was also popularly used in dentistry in the past before more advanced replacements came into the market. This is because it is the most malleable of all metals and does not readily react with the air. Gold can also be hammered into thin sheets, or gold leaf, and is often used in electroplating. Gold is also quite rare and therefore holds great value all over the world. For this reason, gold is not used in piping. For the same reason, it was used as a type of currency. As mentioned before, the United States used to function on the gold standard, but that was later discarded for the current method. Even though we no longer operate on the gold standard, gold bars are still traded today in certain markets. Gold can also be used medicinally. It has been found to help those suffering from severe rheumatoid arthritis as an anti-inflammatory drug.
Reactions with acids
Cu and Ag are able to react with H2SO4(aq) or HNO3(aq) Thus shifting the oxidation numbers of Cu and Ag to Cu2+ and Ag+. However, Au will not react with either H2SO4(aq) or HNO3(aq), rather it will react with what is called aqua water, which is one part HNO3 and three parts HCl. For example,
Au(s) + 4H+(aq) + NO3-(aq) + 4Cl-(aq) → [AuCl4]-(aq) + 2H2O(l) + NO(g)
Note: The group 11 metals do not react with hydrochloric acid.
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