Palladium (Pd)

Science / Periodic Table of Elements / Palladium (Pd): Atomic number: 46, Atomic mass: 106.42 g.mol -1, Electronegativity: 2.2, Density: 11.9 at 20°C, Melting point: 1560 °C, Boiling point: 2927 °C, Isotopes: 9, Vanderwaals radius: 0.065 nm (+2), Ionic radius: 0.137 nm, Electronic shell: [ Kr ] 4d10 5s0, Energy of first ionisation: 703 kJ.mol -1, Energy of second ionisation: 1870 kJ.mol -1, Energy of third ionisation: 3177 kJ.mol -1, Standard potential: + 0.85 V (Pd2+/ Pd ), Discovered by: William Wollaston in 1803. Palladium, together with rhodium, ruthenium, osmium, iridium, and platinum form a group of elements referred to as the platinum group metals (PGM). Palladium is a lustrous silver-white metal. It has a face-centered cubic crystalline structure, at ordinary temperatures it is strongly resistant to corrosion in air and to the action of acids. It is attacked by hot acids, and it dissolves in aqua regia. It forms many compounds and several complex salts. Palladium has a great ability to absorb hydrogen (up to 900 times its own volume). Applications: Because of its corrosion resistance, a major use of palladium is in alloys used in low voltage electrical contacts. When it is finely divided, palladium forms a good catalyst and is used to speed up hydrogenation and dehydrogenation reactions. Palladium is used extensively in jewelry-making in certain alloys called "white gold." It may be alloyed with platinum or substituted for it. It is used in watch bearings, springs, and balance wheels and also for mirrors in scientific instruments. In 1990, most catalytic converters relied on platinum to reduce emissions from car exhausts but, while this metal is still important, palladium is now the main ingredient because this is even more efficient at removing unburnt and partially burnt hydrcarbons from the fuel. Palladium is nowadays more and more used in electrical appliances such as wide screen televisions, computers and mobile phones, in the form of tiny multi-layer ceramic capacitors, of which more than 400 billion are made each year. For use in dentistry it is alloyed with silver, gold, and copper. Palladium salts are used in electroplating. Palladium in the environment: Specimen of uncombined palladium are found in Brazil, and there are some minerals rich in palladium, but most of it is extracted as a by-product form nickel refining. Palladium is found as the free metal associated with platinum and other platinum group metals in Australia, Brazil, Russia, Ethiopia, and North and South America, as well as with nickel and copper deposits (from which it is recovered commercially) in Canada and South Africa.