Palladium (Pd)

Stable isotopes of palladium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
Pd-102 46 56 101.905607 1.02% >96.00% Metal
Pd-104 46 58 103.904034 11.14% 86.00-98.00% Metal
Pd-105 46 59 104.905083 22.33% 94.00-98.00% Metal
Pd-106 46 60 105.903484 27.33% 95.00-98.00% Metal
Pd-108 46 62 107.903895 26.46% >99.00% Metal
Pd-110 46 64 109.90515 11.72% >99.00% Metal

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Palladium was discovered in 1803 by William Hyde Wollaston. It is named for the asteroid Pallas, which was discovered at about the same time, as well as for the Greek name Pallas, goddess of wisdom.

A silver-white, ductile metal, palladium has a face-centered cubic crystalline structure and does not tarnish in air. It is the least noble (most reactive) of the platinum group and can absorb up to 800 times its own volume of hydrogen. Upon doing so, the metal swells, becoming brittle and cracked. Such absorption of hydrogen decreases the electrical conductivity of the metal. Also, such absorption activates molecular hydrogen, dissociating it to atomic hydrogen. It is attacked by hot, concentrated nitric acid and boiling sulfuric acid. It is soluble in aqua regia, fused alkalis, hot nitric acid and boiling sulfuric acid, and insoluble in organic acids and water. It is a good electrical conductor. It is nontoxic and noncombustible, except as dust. The metal forms mostly bivalent compounds, although a small number of tetravalent and fewer trivalent compounds are known. Palladium exhibits a strong tendency to form complexes, and it dissolves more oxygen in its molten state than in solid form. Palladium reacts with fluorine and chlorine at 500 ºC, forming its halides. Hydrochloric acid has no effect on the metal.

One of the most important applications of palladium is to catalyze hydrogenation, dehydrogenation and petroleum cracking. Such reactions are widely employed in organic syntheses and petroleum refining. Palladium and platinum are installed in catalytic converters in automobiles to cut down the emission of unsaturated hydrocarbon gases.

Properties of Palladium

Name Palladium 
Symbol Pd 
Atomic number 46
Atomic weight 106.42
Standard state Solid at 298 °K
CAS Registry ID 7440-05-3
Group in periodic table 10
Group name Precious metal or platinum group metal
Period in periodic table 5
Block in periodic table d-block
Color Silvery white metallic
Classification Metallic
Melting point 1554 °C
Boiling point 2970 °C
Thermal conductivity 71.8 W/(m·K) at 298.2 °K
Electrical resistivity 10.54 µΩ·cm at 20 °C
Electronegativity 2.2
Specific heat 0.24 kJ/kg K
Heat of vaporization 380 kJ·mol-1 at 2970 °C
Heat of fusion 16.7 kJ·mol-1
Density of liquid 10.38 g/cm3 at 1554 °C
Density of solid 12.02 g/cm3
Electron configuration [Kr]4d10
Atomic radius 1.375 Å
Ionic radius Pd2+ (coordination number 4, square planar): 0.64 Å
Oxidation states +2, +3, +4
Most common oxidation state +2

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