Palladium
Element 46 · Transition Metal
Palladium is the least dense of the precious metals and the only element whose ground-state electron configuration has a completely filled 4d shell with no 5s electrons. It is best known for two jobs: cleaning car exhaust in catalytic converters and selectively absorbing hydrogen — palladium membranes let hydrogen pass through while blocking every other gas. It is also a gifted catalyst in organic chemistry, where palladium compounds stitch carbon atoms together in reactions that won the 2010 Nobel Prize in Chemistry. Named after the asteroid Pallas, palladium has become one of the most industrially critical of the precious metals.
Key facts
| Atomic number | 46 |
|---|---|
| Atomic weight | 106.42 |
| Category | Transition Metal |
| Group / Period | 10 / 5 |
| Block | d |
| Electron configuration | [Kr] 4d10 |
| Common oxidation states | +2, +4 |
| State at STP | Solid |
| Electronegativity | 2.20 |
| Atomic radius | 137 pm (empirical) |
| Density | 12.023 g/cm³ |
| Melting point | 1555 °C |
| Boiling point | 2963 °C |
Occurrence
Palladium occurs with platinum-group metals in ores mined in South Africa, Russia, and North America, and it is also recovered from nickel and copper refining. Growing amounts are recycled from spent catalytic converters.
Applications
Catalytic converters
Electronics and multilayer capacitors
Hydrogen storage and purification
Jewelry and dental alloys
Common compounds
- Palladium chloride
- Palladium on carbon (catalyst)
- Palladium acetate
Palladium can absorb up to 900 times its own volume of hydrogen gas — a property that makes it uniquely useful for purifying hydrogen.
Data source: IUPAC standard atomic weights 2021; NIST physical property data