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Palladium

2007 Schools Wikipedia Selection. Related subjects: Chemical elements


                46              rhodium ← palladium → silver
                Ni
                ↑
                Pd
                ↓
                Pt

                                  Periodic Table - Extended Periodic Table

                                                                   General
                                    Name, Symbol, Number palladium, Pd, 46
                                         Chemical series transition metals
                                             Group, Period, Block 10, 5, d
                                         Appearance silvery white metallic
                                              Atomic mass 106.42 (1) g/mol
                                         Electron configuration [Kr] 4d^10
                                       Electrons per shell 2, 8, 18, 18, 0
                                                       Physical properties
                                                               Phase solid
                                     Density (near r.t.) 12.023 g·cm^−3
                                   Liquid density at m.p. 10.38 g·cm^−3
                                                  Melting point 1828.05  K
                                               (1554.9 ° C, 2830.82 ° F)
                                                      Boiling point 3236 K
                                                    (2963 ° C, 5365 ° F)
                                         Heat of fusion 16.74 kJ·mol^−1
                                     Heat of vaporization 362 kJ·mol^−1
                          Heat capacity (25 °C) 25.98 J·mol^−1·K^−1

   CAPTION: Vapor pressure

                                      P/Pa   1    10  100  1 k  10 k 100 k
                                     at T/K 1721 1897 2117 2395 2753 3234

                                                         Atomic properties
                                     Crystal structure cubic face centered
                                                      Oxidation states ±1
                                                      (mildly basic oxide)
                                    Electronegativity 2.20 (Pauling scale)
                                     Ionization energies 1st: 804.4 kJ/mol
                                                          2nd: 1870 kJ/mol
                                                          3rd: 3177 kJ/mol
                                                      Atomic radius 140 pm
                                              Atomic radius (calc.) 169 pm
                                                    Covalent radius 131 pm
                                               Van der Waals radius 163 pm
                                                             Miscellaneous
                                                 Magnetic ordering no data
                              Electrical resistivity (20 °C) 105.4 nΩ·m
                       Thermal conductivity (300 K) 71.8 W·m^−1·K^−1
                       Thermal expansion (25 °C) 11.8 µm·m^−1·K^−1
                               Speed of sound (thin rod) (20 °C) 3070 m/s
                                                   Young's modulus 121 GPa
                                                      Shear modulus 44 GPa
                                                      Bulk modulus 180 GPa
                                                        Poisson ratio 0.39
                                                        Mohs hardness 4.75
                                                  Vickers hardness 461 MPa
                                                 Brinell hardness 37.3 MPa
                                             CAS registry number 7440-05-3
                                                         Selected isotopes

                CAPTION: Main article: Isotopes of palladium

                          iso     NA   half-life  DM    DE ( MeV)     DP
                         ^100Pd syn    3.63 d     ε   -             ^107Rh
                                                  γ   0.084, 0.074,
                                                      0.126         -
                         ^102Pd 1.02%  Pd is stable with 56 neutrons
                         ^103Pd syn    16.991 d   ε   -             ^103Rh
                         ^104Pd 11.14% Pd is stable with 58 neutrons
                         ^105Pd 22.33% Pd is stable with 59 neutrons
                         ^106Pd 27.33% Pd is stable with 60 neutrons
                         ^107Pd syn    6.5×10^6 y β^- 0.033         ^107Ag
                         ^108Pd 26.46% Pd is stable with 62 neutrons
                         ^110Pd 11.72% Pd is stable with 64 neutrons

                                                                References

   Palladium ( IPA: /pəˈleɪdiəm/) is a chemical element with symbol Pd and
   atomic number 46. A rare silver-white transition metal of the platinum
   group, palladium resembles platinum chemically and is extracted from
   some copper and nickel ores. It is primarily used as an industrial
   catalyst and in jewelry.

Notable characteristics

   Palladium.
   Enlarge
   Palladium.

   Palladium is a soft silver-white metal that resembles platinum. It is
   the least dense and has the lowest melting point of the platinum group
   metals. It is soft and ductile when annealed and greatly increases its
   strength and hardness when it is cold-worked. Palladium is chemically
   attacked by sulfuric, nitric and hydrochloric acid in which it
   dissolves slowly. This metal also does not react with oxygen at normal
   temperatures (and thus does not tarnish in air). Palladium heated to
   800°C will produce a layer of palladium(II) oxide (PdO). It lightly
   tarnishes in moist atmosphere containing sulfur.

   This metal has the uncommon ability to absorb up to 900 times its own
   volume of hydrogen at room temperatures. It is thought that this
   possibly forms palladium hydride (PdH[2]) but it is not yet clear if
   this is a true chemical compound.

   When palladium has absorbed large amounts of hydrogen, it can swell up,
   like a sponge full of water, visible to the naked eye.

   Common oxidation states of palladium are 0,+1, +2 and +4. Although
   originally +3 was thought of as one of the fundamental oxidation states
   of palladium, there is no evidence for palladium occurring in the +3
   oxidation state; this has been investigated via X-ray diffraction for a
   number of compounds, indicating a dimer of palladium(II) and
   palladium(IV) instead. Recently, compounds with an oxidation state of
   +6 were synthesised.

Applications

   When it is finely divided, palladium forms a good catalyst and is used
   to speed up hydrogenation and dehydrogenation reactions, as well as in
   petroleum cracking. A large number of carbon-carbon bond forming
   reactions in organic chemistry (such as the Suzuki coupling) are
   facilitated by catalysis with palladium compounds. It is also alloyed
   and used in jewelry. Other uses;
     * The largest use of palladium today is in catalytic converters. Much
       research is in progress to discover ways to replace the much more
       expensive platinum with palladium in this application.
     * Palladium is one of three metals which can be alloyed with gold to
       produce White gold. (Nickel and Silver can also be used.)
     * Similar to gold, palladium can be beaten into a thin leaf form as
       thin as 100 nm (1/250,000 in).
     * Since 1939 palladium itself has occasionally been used as a
       precious metal in jewelry, often as a replacement for platinum. (
       ).
     * Hydrogen easily diffuses through heated palladium; thus, it
       provides a means of purifying the gas. Also, hydrogen dissolved in
       palladium is highly reactive, allowing it to be used in various
       chemical reductions.
     * Palladium (and palladium-silver alloys) are used as electrodes in
       multi-layer ceramic capacitors.
     * Palladium (sometimes alloyed with nickel) is used in connector
       platings in consumer electronics.
     * Palladium is also used in dentistry , watch making, in aircraft
       spark plugs and in the production of surgical instruments and
       electrical contacts.
     * Palladium is also used to make professional transverse flutes.
     * It is also used as Palladium-Hydrogen electrode in electrochemical
       studies.
     * Palladium dichloride can absorb large amounts of carbon monoxide
       gas, and is used in carbon monoxide detectors.

History

   Palladium was discovered by William Hyde Wollaston in 1803. This
   element was named by Wollaston in 1804 after the asteroid Pallas, which
   was discovered two years earlier.

   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, Na OH, precipitating platinum as ammonium
   chloroplatinate through treatment with ammonium chloride, NH[4]Cl, and
   then adding mercuric cyanide to form the compound palladium cyanide.
   Finally, he heated the resulting compound in order to extract palladium
   metal.

   The compound palladium chloride was at one time prescribed as a
   tuberculosis treatment at the rate of 0.065g per day (approximately one
   milligram per kilogram of body weight). This treatment did not have
   many negative side effects, but was later replaced by more effective
   drugs.

   The element played an essential role in the Fleischmann-Pons
   experiment, also known as cold fusion.

   In 2000, Ford Motor Company created a price bubble in palladium by
   stockpiling large amounts of the metal, fearing interrupted supplies
   from Russia. As prices fell in early 2001, Ford lost nearly $1 billion
   U.S. dollars.

Occurrence

   Palladium is found as a free metal and alloyed with platinum and gold
   with platinum group metals in placer deposits of the Ural Mountains,
   Australia, Ethiopia, South and North America. It is commercially
   produced from nickel-copper deposits found in South Africa, Ontario and
   Siberia; the huge volume of ore processed makes this extraction
   profitable in spite of the low proportion of palladium in these ores.
   The world's largest single producer of Palladium is MMC Norilsk Nickel,
   headquartered in Moscow.

   About the possibility of producing palladium in reactors or extracting
   it from spent nuclear fuel, see Synthesis of noble metals.

Isotopes

   Naturally-occurring palladium is composed of six isotopes. The most
   stable radioisotopes are ^107Pd with a half-life of 6.5 million years,
   ^103Pd with a half-life of 17 days, and ^100Pd with a half-life of 3.63
   days. Eighteen other radioisotopes have been characterized with atomic
   weights ranging from 92.936 u (^93Pd) to 119.924 u (^120Pd). Most of
   these have half-lifes that are less than a half an hour except ^101Pd
   (half-life: 8.47 hours), ^109Pd (half-life: 13.7 hours), and ^112Pd
   (half-life: 21 hours).

   The primary decay mode before the most abundant stable isotope, ^106Pd,
   is electron capture and the primary mode after is beta decay. The
   primary decay product before ^106Pd is rhodium and the primary product
   after is silver.

   Radiogenic ^107Ag is a decay product of ^107Pd and was first discovered
   in the Santa Clara, California meteorite of 1978. The discoverers
   suggest that the coalescence and differentiation of iron-cored small
   planets may have occurred 10 million years after a nucleosynthetic
   event. ^107Pd versus Ag correlations observed in bodies, which have
   clearly been melted since accretion of the solar system, must reflect
   the presence of short-lived nuclides in the early solar system.
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