In the periodic table of elements, six metallic elements are bunched together in the d-block, specifically in groups 8 to 9, periods 5 and 6. All transition metals, these six elements are collectively referred to as the "platinum group metals". These precious metals tend to occur with one another in mineral deposits. Likewise, they are alike in both chemical and physical properties.
In the order of their arrangement in the periodic table, the six metallic elements of the platinum group are ruthenium, rhodium, palladium, osmium, iridium, and platinum. A brief description of each of these precious metals is provided below.
1. Ruthenium - This element is represented by the symbol Ru. Its atomic number is 44. It is mostly found in platinum ores and often used in platinum alloys as a catalyst. Its two main physical characteristics refer to its hardness as a metal and to its silvery-white color. The former characteristic makes ruthenium ideal for use in making wear-resistance electrical contacts. The price of this precious metal as of January 2010 is estimated to be about USD173 per troy ounce (USD5,562 per kilogram).
2. Rhodium - This element is represented by the symbol Rh. Its atomic number is 45. Its occurrence is similar to that of ruthenium, and its primary use is as a catalytic converter. Rhodium is considered perhaps the rarest element. It is also known to be the most expensive precious metal, with a price estimated to be about USD2,750 per troy ounce (USD88,415 per kilogram) as of January 2010.
3. Palladium - This element is represented by the symbol Pd. Its atomic number is 46. It is also considered one of the rarest precious metals. Palladium closely resembles its co-member in the platinum group - platinum. It is soft and is silvery-white in color. Like rhodium, palladium is largely used as a catalytic converter. As of January 2010, the price of this metal is estimated to be approximately USD424 per troy ounce (USD13,632 per kilogram).
4. Osmium - This element is represented by the symbol Os. Its atomic number is 76. It is found in nature as an alloy in platinum ores. Osmium is considered the densest natural element. It is brittle and is blue-gray in color. Because of its hardness, osmium is alloyed with the other metals in its group and used in electrical contacts and high-quality fountain pen tips. The price of osmium, as of January 2010, is about USD32.15 per troy ounce (USD12,217 per kilogram).
5. Iridium - This element is represented by the symbol Ir. Its atomic number is 77. Like osmium, iridium is very hard and brittle; it has a different color though - silvery-white. Its principal use is for electrical purposes, mainly because of its density and its high resistance to corrosion even at extremely high temperatures. Iridium is considered the fourth least abundant element in the Earth's crust, after rhenium, ruthenium, and rhodium. Its price is estimated to be about USD408 per troy ounce (USD13,117 per kilogram) as of January 2010.
6. Platinum - This element, after which this group of precious metals is named, is represented by the symbol Pt. Its atomic number is 78. Platinum is dense, ductile, and malleable; it is gray-white in color. Known to be highly resistant to corrosion, this precious metal is used in jewelry, electrical contacts, and laboratory equipment. Its price, as of January 2010, is USD1,555 per troy ounce (USD49,995 per kilogram), making it the second most expensive precious metal, after rhodium.
Evident from the description of each of these six precious metals is that all of them have outstanding catalytic properties and high resistance to tarnish and wear. These characteristics make any of them well suited for fine jewelry. Additionally, their excellent resistance to extremely high temperatures makes them ideal for many different industrial uses.