Palladium
Atomic Data
| Atomic Number | 46 |
| Symbol | Pd |
| Atomic Weight | 106.42 u |
| Density (STP) | 12.023 g/cm³ |
| Melting Point | 1554.9 °C (1828.05 K) |
| Boiling Point | 2962.85 °C (3236 K) |
| Electronegativity | 2.2 (Pauling) |
| Electron Config. | 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 |
| Oxidation States | +2, +4 |
| Phase at STP | Solid |
| Category | Transition Metal |
| Period / Group | 5 / 10 |
| CAS Number | 7440-05-3 |
Electron Configuration
[Kr] 4d10
| Shell | n | Subshell | Electrons | Cumulative |
|---|---|---|---|---|
| K | 1 | 1s | 2 | 2 |
| L | 2 | 2s | 2 | 4 |
| L | 2 | 2p | 6 | 10 |
| M | 3 | 3s | 2 | 12 |
| M | 3 | 3p | 6 | 18 |
| M | 3 | 3d | 10 | 28 |
| N | 4 | 4s | 2 | 30 |
| N | 4 | 4p | 6 | 36 |
| N | 4 | 4d | 10 | 46 |
| Total | 46 | 46 | ||
Isotopes of Palladium
Palladium has six naturally occurring stable isotopes. The most abundant is ¹⁰⁶Pd, comprising 27.33% of all naturally occurring Palladium.
| Isotope | Symbol | Protons | Neutrons | Abundance | Stability |
|---|---|---|---|---|---|
| Palladium-102 | ¹⁰²Pd | 46 | 56 | 1.02 | Stable |
| Palladium-104 | ¹⁰⁴Pd | 46 | 58 | 11.14 | Stable |
| Palladium-105 | ¹⁰⁵Pd | 46 | 59 | 22.33 | Stable |
| Palladium-106 | ¹⁰⁶Pd | 46 | 60 | 27.33 | Stable |
| Palladium-108 | ¹⁰⁸Pd | 46 | 62 | 26.46 | Stable |
| Palladium-110 | ¹¹⁰Pd | 46 | 64 | 11.72 | Stable |
Abundance & Occurrence
Palladium is present in Earth's crust at approximately 0.0006 ppm by mass and at approximately 2 ppm by mass throughout the universe.
Earth's Crust (ppm by mass)
Universe (ppm by mass)
Discovery & History
Read more about the discovery of the periodic table of elements →
Safety & Handling
- Palladium compound toxicity: Soluble palladium salts (PdCl2, Pd(NO3)2) are moderately toxic by ingestion and inhalation; they cause irritation of the respiratory tract and may cause kidney damage with systemic exposure.
- Sensitisation and allergy: Like other platinum group metals, palladium can cause occupational contact dermatitis and respiratory sensitisation; dental alloys containing palladium have caused oral mucosa hypersensitivity in some patients.
- Hydrogen absorption hazard: Palladium absorbs large volumes of hydrogen gas; heavily hydrogen-loaded palladium can release hydrogen rapidly on heating: be aware of fire and explosion risk in hydrogen-charged palladium systems.
- General handling: Bulk palladium metal has low acute toxicity; standard precautions (dust control, ventilation for powder handling) are appropriate for laboratory and industrial use.
Palladium in the Real World
Real-World Uses
- Automotive catalytic converters: Palladium oxidises carbon monoxide and unburned hydrocarbons in gasoline-engine catalytic converters; it is now used in larger quantities than platinum in modern three-way catalysts due to superior performance under lean-burn conditions.
- Multilayer ceramic capacitors (MLCCs): Palladium and palladium-silver alloy internal electrodes are used in high-capacitance MLCCs for decoupling and filtering in mobile phones, computers, and automotive electronics.
- Hydrogen purification: Palladium membranes allow only hydrogen to diffuse through the metal lattice; thin Pd or Pd-Ag membranes produce ultra-pure hydrogen for fuel cells, semiconductor fabrication, and speciality chemical synthesis.
- Pharmaceutical synthesis: Palladium complexes catalyse Suzuki, Heck, and Negishi cross-coupling reactions that form carbon-carbon bonds, enabling efficient synthesis of active pharmaceutical ingredients and agrochemicals.
- Jewellery: Palladium is alloyed with gold to make white gold, or used as a lightweight precious metal in its own right for rings and watch components; it is hypoallergenic and retains its white colour without rhodium plating.
Downloadable Resources
Free periodic table reference sheets for classrooms, study sessions, and laboratory use.
Frequently Asked Questions
What is palladium used for?
Palladium is used in catalytic converters (alongside platinum and rhodium) to oxidise carbon monoxide and unburned hydrocarbons in vehicle exhaust. It is also used extensively in electronics: palladium is a component of multilayer ceramic capacitors (MLCCs) found in virtually every electronic device. In chemistry, palladium catalysts enable cross-coupling reactions central to pharmaceutical synthesis, earning the 2010 Nobel Prize in Chemistry.
Can palladium absorb hydrogen?
Yes, palladium has a remarkable ability to absorb hydrogen gas: up to about 900 times its own volume at room temperature. Hydrogen atoms dissociate on the palladium surface and diffuse into the crystal lattice between palladium atoms. This property makes palladium useful for hydrogen purification (thin palladium membranes are highly selective for hydrogen) and has attracted interest for hydrogen storage applications.
How was palladium discovered?
Palladium was discovered in 1803 by British chemist William Hyde Wollaston while refining platinum ore. He separated palladium by dissolving the ore in aqua regia and selectively precipitating the new metal. Wollaston named it after the asteroid Pallas, which had been discovered just the year before. He published the discovery only in 1804 after first offering the pure metal for sale anonymously.
What are palladium-catalysed cross-coupling reactions?
Palladium-catalysed cross-coupling reactions join two organic molecules at a carbon-carbon bond: a bond that is otherwise very difficult to form selectively. Reactions such as the Suzuki, Heck, and Negishi couplings are workhorses of modern pharmaceutical synthesis, enabling the efficient assembly of complex drug molecules. The 2010 Nobel Prize in Chemistry was awarded to Richard Heck, Ei-ichi Negishi, and Akira Suzuki for developing these reactions.