|
|
Atomic Number: |
46 |
Melting Point: | 1554.9 șC | |
| Atomic Symbol: | Pd | Boiling Point: | 2963 șC | ||
| Atomic Weight: | 106.4 amu | Density: | 12023
kg/m 3 |
||
| Atomic Radius: |
138 pm |
Oxidation States: | 3, 2 | ||
| Covalent Radius: | 131 pm | Electron Configuration: | [Kr]4d10 | ||
| van der Waals Radius: |
163 pm |
State of Matter: | solid |
Discovered in 1803 by William Hyde Wollaston, palladium was named after the asteroid Pallas, which was discovered at about the same time. Pallas was the Greek goddess of wisdom.
Wollaston found element 46 in crude platinum ore from South America. He did this by dissolving the ore in aqua regia, neutralizing the solution with sodium hydroxide, precipitating platinum as ammonium chloroplatinate through treatment with ammonium chloride, and then adding mercuric cyanide to form the compound palladium cyanide. Finally, he heated the resulting compound in order to extract palladium metal.
The element is a steel-white metal, it does not tarnish in air, and it is the least dense and lowest melting of the platinum group of metals. When annealed, it is soft and ductile; cold-working greatly increases its strength and hardness. Palladium is attacked by nitric and sulfuric acid.
At room temperatures, the metal has the unusual property of absorbing up to 900 times its own volume of hydrogen, possibly forming Pd2H. It is not yet clear if this is a true compound. Hydrogen readily diffuses through heated palladium, providing a means of purifying the gas.
Common oxidation states of palladium are +2, +3 and +4. Recently, palladium compounds in which palladium has oxidation state +6 were synthesized.
Palladium is found with platinum and other metals of the platinum group in placer deposits of Russia, South America, North America, Ethiopia, and Australia. It is also found associated with the nickel-copper deposits of South Africa and Ontario. Palladium's separation from the platinum metals depends upon the type of ore in which it is found.
Finely divided palladium is a good catalyst and is used for hydrogenation and dehydrogenation reactions. It is alloyed and used in jewelry trades.
White gold is an alloy of gold decolorized by the addition of palladium. Like gold, palladium can be beaten into leaf as thin as 1/250,000 in. The metal is used in dentistry, watch making, and in making surgical instruments and electrical contacts.
Naturally-occurring palladium is composed of six isotopes. The most stable radioisotopes are Pd-107, Pd-103, and Pd-100. Eighteen other radioisotopes have been characterized.
There are no serious hazards associated with palladium. Proper safety precautions should be exercised when handling any type of metal.
