Palladium
transition metalProperties
| Property | Value |
|---|---|
| Atomic Mass | 106.42 amu |
| Category | transition metal |
| Group | 10 |
| Period | 5 |
| Electron Configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 4d10 |
| Electronegativity | 2.2 (Pauling) |
| Oxidation States | 2, 4, 0 |
| Melting Point | 1828.05 K (1554.9 °C) |
| Boiling Point | 3236 K (2962.8 °C) |
| Density | 12.023 g/cm³ |
| Discovered By | William Hyde Wollaston (1803) |
About Palladium
Palladium has the strangest ground-state electron configuration of any element: [Kr] 4d¹⁰ 5s⁰. Every other transition metal keeps at least one electron in its outermost s-orbital, but in Pd the 5s electrons drop into the 4d shell to give a closed d¹⁰ subshell — which is why its chemistry rides on Pd(0)/Pd(II) cycling instead of the usual transition-metal range. That oxidation-state shuttle is the reason a generation of pharmaceutical chemists owes Pd a thank-you note. The Heck, Suzuki-Miyaura, and Negishi cross-couplings — Nobel 2010 — all hinge on a Pd(0) center oxidatively adding into an aryl halide and then reductively eliminating after transmetallation. The same metal absorbs hydrogen the way a sponge absorbs water, swelling to take up roughly 900 times its own volume of H₂ at room temperature into its octahedral lattice holes; thin Pd or Pd-Ag membranes give you the cleanest hydrogen on the planet. Most newly mined Pd comes out of the Bushveld and Norilsk and ends up in three-way catalytic converters scrubbing CO and NOₓ from gasoline exhaust.
Fun Fact
A piece of palladium foil at room temperature can absorb about 900 times its own volume in hydrogen — the H₂ dissociates on the surface, the protons and electrons go separate ways into the lattice, and the metal swells visibly. Heat it and the hydrogen comes back out, which is how Pd-Ag membranes are used to deliver six-nines-pure H₂ to semiconductor fabs.
Common Uses
- Pd(0) catalysis for Suzuki, Heck, Negishi, and Buchwald-Hartwig cross-couplings in API synthesis
- Three-way catalytic converters in gasoline vehicles (CO + NOₓ + HC abatement)
- Pd-Ag membranes for ultra-pure hydrogen separation in fuel-cell and semiconductor lines
- Pd-on-carbon for hydrogenation and hydrogenolysis (debenzylation, alkene reduction)
- Multilayer ceramic capacitor (MLCC) inner electrodes in electronics