46 Pd 106.42

Palladium

Transition metal Palladium solid

[Kr] 4d¹⁰ · 2 · 8 · 18 · 18

← Rh Rhodium Ag Silver →

A platinum metal that can soak up nine hundred times its own volume of hydrogen. Palladium is indispensable in petrol-engine catalytic converters and in hydrogen technology.

3D model

Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.

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Atomic properties

Atomic number: 46
Atomic mass: 106.42 а.е.м.
Electron configuration: [Kr] 4d¹⁰
Electrons per shell: 2 · 8 · 18 · 18
Block: d-block
Group: Nickel group
Period: 5
Electronegativity (Pauling): 2.2
Electronegativity (Allen): 1.59
Atomic radius: 169 pm
Covalent radius: 139 pm
Van der Waals radius: 202 pm
Ionisation energy 1: 804.4 kJ/mol
Ionisation energy 2: 1 870 kJ/mol
Ionisation energy 3: 3 177 kJ/mol
Electron affinity: 53.7 kJ/mol
Common oxidation states: +2, +4
Oxidation states: 0, +1, +2, +3, +4, +5, +6

Physical properties

State at 25 °C: solid
Density: 12.023 g/cm³
Melting point: 1 828.05 K · 1 554.9 °C
Boiling point: 3 236 K · 2 962.9 °C
Speed of sound: 3 070 m/s

Thermal properties

Heat of fusion: 16.74 kJ/mol
Heat of vaporisation: 358 kJ/mol
Specific heat capacity: 0.246 J/(g·K)
Thermal conductivity: 71.8 W/(m·K)

Mechanical properties

Young's modulus: 121 GPa
Shear modulus: 44 GPa
Bulk modulus: 180 GPa
Poisson ratio: 0.39
Mohs hardness: 4.75
Brinell hardness: 37.3 MPa

Electrical and magnetic properties

Electrical resistivity: 105.4 nΩ·m
Magnetic ordering: paramagnetic
Curie point: no data
Néel point: no data
Superconducting point: no data

Crystal structure

Crystal structure: face-centred cubic (fcc)
Lattice constants: a = 389.07 pm

Abundance

In the crust: 0.015 mg/kg
In the ocean: no data
In the universe: 0.2 mg/kg
In the human body: no data

Isotopes

Isotope	Abundance	Half-life	Decay mode
¹⁰²Pd	1.02 %	stable	—
¹⁰⁴Pd	11.14 %	stable	—
¹⁰⁵Pd	22.33 %	stable	—
¹⁰⁶Pd	27.33 %	stable	—
¹⁰⁸Pd	26.46 %	stable	—
¹¹⁰Pd	11.72 %	stable	—

Palladium-107, half-life 6.5 million years, is a long-lived fission product. Palladium-103 is used in prostate brachytherapy.

Discovery

Year of discovery: 1802
Discovered by: William Hyde Wollaston
Where: England
Origin of the name: after the asteroid Pallas, discovered a year earlier

History

Wollaston discovered palladium in 1802 and, instead of publishing, sold it anonymously from a London shop as "new silver". The exposure caused a scandal, after which he did publish.

Where it occurs

0.015 mg/kg of the crust. Mined with platinum and nickel; the largest producers are Russia (Norilsk) and South Africa.

How it is produced

From copper-nickel concentrates and platinum ores. A large share now comes from recycling spent catalytic converters.

Role in living things

No biological role, though traces occur in the body from vehicle emissions.

Safety

The metal is of low toxicity, but palladium is a notable contact allergen, particularly in dental alloys.

Uses

Petrol-engine catalytic converters — over 80 % of consumption
Ultra-pure hydrogen membranes: palladium lets nothing but hydrogen through
Multilayer ceramic capacitors in electronics
White gold alloys and jewellery in its own right
Cross-coupling catalysts in organic synthesis

Curiosities

Palladium cross-coupling won the 2010 Nobel Prize in Chemistry and underpins the synthesis of most modern drugs.
Palladium is named after the asteroid Pallas, discovered a year before the element.
The 1989 cold fusion claim was made on a palladium electrode; the result was never reproduced.
A palladium membrane a fraction of a millimetre thick delivers hydrogen at 99.9999 % purity.