Palladium
Palladium is a chemical element with symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas.
Identity
- Atomic mass
- 106.421 u
- Category
- Transition metals
- Group
- 10
- Period
- 5
- Block
- d
- Oxidation States
- +2, +4
- Phase (25 °C)
- Solid
- Appearance
- silvery white
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 4d10
- Short configuration
- [Kr] 4d10
- Electrons per shell
- 2, 8, 18, 18
- Electronegativity (Pauling)
- 2.20
- Electron affinity
- 54.2 kJ/mol
- 1st ionization energy
- 804 kJ/mol
- Ionization energies
- 804 · 1870 · 3177 kJ/mol
Physical properties
- Melting point
- 1554.9 °C (1828 K)
- Boiling point
- 2962.8 °C (3236 K)
- Density
- 12.023 g/cm³
- Molar heat capacity
- 26.0 J/(mol·K)
Chemical behavior of palladium
Palladium is a group 10 transition metal with symbol Pd and atomic number 46. It is a silvery platinum-group metal, resistant to heat and corrosion. Its main state is +2, with +4 in some complexes. Famous for absorbing hydrogen and catalyzing cross-coupling, it serves car catalysts, electronics and jewelry.
Reactivity
Pd + 2 Cl2 -> PdCl4
Palladium reacts with chlorine to form palladium tetrachloride, a bluish-gray solid that is the most stable compound.
Pd + 2 HNO3(Hcl) -> PdO2 + 2 NO2 + H2O
Palladium reacts with nitric and hydrochloric acid, releasing nitrogen dioxide and forming palladium tetroxide.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Palladium(II) chloride | PdCl2 | Brown solid; getter and catalyst precursor |
| Palladium tetrachloride | PdCl4 | Bluish-gray solid; getter precursor and used in electrorefining |
| Palladium tetroxide | PdO2 | Orange solid; getter precursor and used in hydrogen adsorption |
Electron shell distribution
View in the atom builderIsotopes
Natural palladium has six stable isotopes: palladium-106 (27.3 %), palladium-108 (26.5 %), palladium-105 (22.3 %), palladium-110 (11.7 %), palladium-104 (11.1 %) and palladium-102 (1.0 %). Palladium-107 is slightly radioactive with a 6.5-million-year half-life.
Occurrence and production
Trace platinum-group element in cooperite, braggite and nickel-copper sulfide ores. Main supply as by-product of platinum-nickel mining in South Africa, Russia, Canada and the United States.
History and origin of the name
William Hyde Wollaston isolated it in 1803 in London from platinum residues, naming it after the asteroid Pallas (goddess Pallas Athena). Found alongside rhodium, it opened platinum-group chemistry.
Applications and relevance of palladium
Uses of the element
Most goes to gasoline-car catalysts and electronics (contacts, connectors, conductive pastes). White-gold and jewelry alloys use it for pale color and tarnish resistance; dentistry and hydrogen membranes take smaller shares.
Uses of its compounds
Complexes catalyze Suzuki, Heck and Negishi couplings building drugs and fine chemicals. Chloride tests for carbon monoxide and catalyzes Wacker oxidation; membranes purify hydrogen.
Health, safety and environment
Biological role
Palladium is not essential; metal has low toxicity but soluble salts and fine dust irritate skin, eyes and airways and may sensitize some people.
Safety
Metal is stable, yet inorganic palladium compounds, plating mists and catalyst dusts need ventilation, gloves and eye protection. Powder can be flammable when finely divided.
Environment
Mining footprint is large; metal is persistent but inert. High value drives strong recycling of spent car catalysts and electronic scrap.
Frequently asked questions about Palladium
Why does palladium soak up hydrogen?
Hydrogen dissociates on its surface and atoms slip into lattice gaps, swelling the metal reversibly up to about 900 volumes. Uptake depends on pressure, temperature and alloying.
What is palladium's role in making medicines?
It catalyzes carbon-carbon and carbon-nitrogen couplings (Suzuki, Heck, Negishi) assembling complex drug scaffolds from simple pieces. Used catalytically, but residues must be scrubbed.
Why is palladium in electronics?
Conductive, stable and plateable thinly for contacts, connectors and multilayer-ceramic-capacitor electrodes. Design weighs cost, availability and substitution.
Why is palladium price so volatile?
Concentrated mining plus dominant car-catalyst demand against tight recycling lags swing price. Emission rules, substitution with platinum and stockpiling amplify moves.
How does palladium purify hydrogen?
Dense membranes pass only hydrogen: molecules split at the surface, atoms diffuse through, recombine beyond, while other gases are blocked. Gives very pure H2 for industry.
Why use palladium in white gold and jewelry?
Alloyed with gold it gives a naturally pale color plus corrosion resistance and hardness, unlike a surface rhodium flash. Composition tunes tone, workability and price.
Why does palladium matter for hydrogen technology?
Absorption plus catalysis suit membranes, sensors and electrochemical steps around hydrogen production and use. Cost and poisoning push research to thinner layers and alloys.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.