![]() As these metals have become more expensive, their use as coins has decreased and coins of gold and silver are almost exclusively considered collectors' items. Gold, silver and copper are also collectively termed the coinage metals for obvious reasons. ![]() Because of their inertness to corrosion, ruthenium, rhodium, palladium, osmium, iridium, platinum, silver and gold are also known as the noble metals. The platinum metals were first used by the pre-Columbian Americans and were first introduced to the Spanish in 1555. On the other hand, gold, silver, copper, mercury and the platinum metals (platinum, ruthenium, rhodium, palladium, osmium and iridium) can be found in nature as the metals. It is hard to image now, but aluminum was more expensive than gold until late in the second half of the 19th century. Aluminum is one of the most easily oxidized of the metals and it was not isolated as the pure element until 1825 and cost-effective commercial production did not happen for several decades after that. The ability to resist oxidation means that some metals can be found in nature as the elements, while others had to await discovery until the chemistry was developed sufficiently to allow their isolation. A video version is available on Youtube thanks to the Royal Society of Chemistry. The oxidation of copper by nitric acid has become a classical chemical demonstration with interesting color changes that fun to watch. Some are much better electrical conductors than others, some melt at low temperatures while others have very high melting points ( Selected Metal Melting Points), and some are much more easily oxidized than others. Metals have a range of physical and chemical properties. ![]() In the periodic table, the metals lie to the left, and most elements are metals. Metals are a class of the chemical elements that exhibit the properties of ductility, malleability, luster and electrical conductivity.
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