Palladium

Palladium is a chemical element; it has symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1802 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas (formally 2 Pallas), which was itself named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas. Palladium, platinum, rhodium, ruthenium, iridium and osmium form together a group of elements referred to as the platinum group metals (PGMs). They have similar chemical properties, but palladium has the lowest melting point and is the least dense of them.

Palladium, ₄₆Pd

Palladium
Pronunciation	/pəˈleɪdiəm/ ​(pə-LAY-dee-əm)
Appearance	silvery white
Standard atomic weight Ar°(Pd)
	106.42±0.01 106.42±0.01 (abridged)
Palladium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Ni ↑ Pd ↓ Pt rhodium ← palladium → silver
Atomic number (Z)	46
Group	group 10
Period	period 5
Block	d-block
Electron configuration	[Kr] 4d10
Electrons per shell	2, 8, 18, 18
Physical properties
Phase at STP	solid
Melting point	1828.05 K ​(1554.9 °C, ​2830.82 °F)
Boiling point	3236 K ​(2963 °C, ​5365 °F)
Density (at 20° C)	12.007 g/cm3
when liquid (at m.p.)	10.38 g/cm3
Heat of fusion	16.74 kJ/mol
Heat of vaporization	358 kJ/mol
Molar heat capacity	25.98 J/(mol·K)
Vapor pressure P (Pa) 1 10 100 1 k 10 k 100 k at T (K) 1721 1897 2117 2395 2753 3234
Atomic properties
Oxidation states	common: 0, +2, +4 +1, +3, +5
Electronegativity	Pauling scale: 2.20
Ionization energies	1st: 804.4 kJ/mol 2nd: 1870 kJ/mol 3rd: 3177 kJ/mol
Atomic radius	empirical: 137 pm
Covalent radius	139±6 pm
Van der Waals radius	163 pm
Spectral lines of palladium
Other properties
Natural occurrence	primordial
Crystal structure	​face-centered cubic (fcc) (cF4)
Lattice constant	a = 389.02 pm (at 20 °C)
Thermal expansion	11.77×10−6/K (at 20 °C)
Thermal conductivity	71.8 W/(m⋅K)
Electrical resistivity	105.4 nΩ⋅m (at 20 °C)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+567.4×10−6 cm3/mol (288 K)
Young's modulus	121 GPa
Shear modulus	44 GPa
Bulk modulus	180 GPa
Speed of sound thin rod	3070 m/s (at 20 °C)
Poisson ratio	0.39
Mohs hardness	4.75
Vickers hardness	400–600 MPa
Brinell hardness	320–610 MPa
CAS Number	7440-05-3
History
Naming	after asteroid Pallas, itself named after Pallas Athena
Discovery and first isolation	William Hyde Wollaston (1802)
Isotopes of palladium v e
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 100Pd synth 3.63 d ε 100Rh γ – 102Pd 1.02% stable 103Pd synth 16.991 d ε 103Rh 104Pd 11.1% stable 105Pd 22.3% stable 106Pd 27.3% stable 107Pd trace 6.5×106 y β− 107Ag 108Pd 26.5% stable 110Pd 11.7% stable
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More than half the supply of palladium and its congener platinum is used in catalytic converters, which convert as much as 90% of the harmful gases in automobile exhaust (hydrocarbons, carbon monoxide, and nitrogen dioxide) into nontoxic substances (nitrogen, carbon dioxide and water vapor). Palladium is also used in electronics, dentistry, medicine, hydrogen purification, chemical applications, electrochemical sensors, electrosynthesis, groundwater treatment, and jewelry. Palladium is a key component of fuel cells, in which hydrogen and oxygen react to produce electricity, heat, and water.

Ore deposits of palladium and other PGMs are rare. The most extensive deposits have been found in the norite belt of the Bushveld Igneous Complex covering the Transvaal Basin in South Africa; the Stillwater Complex in Montana, United States; the Sudbury Basin and Thunder Bay District of Ontario, Canada; and the Norilsk Complex in Russia. Recycling is also a source, mostly from scrapped catalytic converters. The numerous applications and limited supply sources result in considerable investment interest.