Platinum
Platinum is a transition metal in Group 10 of the periodic table. It is also classified with a group of similar metals, including ruthenium, rhodium, palladium, osmium, and iridium, with similar properties. This group of metals is known as the platinum group. Platinum has an atomic number of 78, an atomic mass of 195.08, and a chemical symbol of Pt.
Properties
Platinum is a silver-gray, shiny metal that is both ductile and malleable. It is so malleable that it can be hammered into a thin sheet no more than about 100 atoms thick. Such a sheet is thinner than aluminum foil. Platinum has a melting point of about 3,223°F (1,773°C), a boiling point of about 6,921°F (3,827°C), and a density of 21.45 grams per cubic centimeter. Its density is one of the highest of all elements.
Platinum is a relatively inactive metal that does not corrode or tarnish in air. It is not attacked by most acids, although it does dissolve in aqua regia (a mixture of concentrated nitric acid and 3-4 parts of hydrochloric acid). Platinum also dissolves in hot alkalis such as hot sodium hydroxide or potassium hydroxide. An unusual property of platinum is that, in powdered form, it tends to absorb large quantities of hydrogen gas.
Occurrence and Extraction
The platinum metals tend to occur together in nature and are relatively difficult to separate from each other. Platinum is one of the rarest of elements with an abundance estimated to be about 10 parts per billion in the Earth's crust. The world's largest supplier of platinum by far is South Africa, which produces about 110,000 kilograms of the metal annually. The next largest source of the metal, Canada, produces less than 10,000 kilograms a year. The only other large producer of platinum is the United States, which gets most of the metal from the Stillwater Mine in Montana.
Discovery and Naming
The first known reference to platinum can be found in the writing of Italian physician, scholar, and poet Julius Caesar Scaliger (1484-1558). Scaliger reported seeing the metal during a visit to Central America in 1557. Natives referred to the metal as platina, or "little silver." They knew of no use for the metal and regarded it as a nuisance in their search for gold and silver. The first complete description of platinum was given by the Spanish military leader Don Antonio de Ulloa (1716-1795). While serving in South America from 1735 to 1746, de Ulloa collected samples of platinum and later wrote a report about his studies on the metal. The name by which the element was known to Central and South Americans was retained as its official chemical name.
Uses
The most important use of platinum is as a catalyst in a variety of industrial operations. For example, platinum is used as a catalyst in the refining and fractionating of petroleum. It is also employed in the production of fertilizers, plastics, synthetic fibers, drugs and pharmaceuticals, and dozens of other everyday products. The application with which most people are likely to be familiar is in catalytic converters in automobile exhaust systems. The metal is also used in other parts of motor vehicle systems, such as spark plugs.
A well-known, but commercially less important, use of platinum is in the manufacture of jewelry. The metal's hardness, resistance to corrosion, and beauty make it ideal for objects such as bracelets, necklaces, earrings, pins, and watch bands.
Platinum also finds applications in systems where chemical inactivity is an important property. For example, artificial pacemakers are often made of platinum alloys because the platinum will not interact with body tissue and cause an allergic reaction. Small amounts of platinum are also used in the manufacture of alloys used in electromagnets. The platinum- cobalt magnet is one of the strongest magnets known.
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