Palladium (Pd)
Palladium (Pd) is a transition metal with atomic number 46 and a standard atomic weight of 106.42. At room temperature it is a solid that melts at 1,555 °C and boils at 2,963 °C.
Palladium key facts
Palladium at a glance
Identity
| Symbol | Pd |
|---|---|
| Atomic number (Z) | 46 |
| Atomic weight | 106.42 ± 0.01 (CIAAW 2024) |
| Category | Transition metal |
| Group | 10 |
| Period | 5 |
| Block | d-block |
| CAS number | 7440-05-3 |
Atomic properties
| Electron configuration | [Kr] 4d10 Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 |
|---|---|
| Electrons per shell | 2, 8, 18, 18 |
| Oxidation states | +2, +4 Less common: +1, +3, +5 |
| Electronegativity (Pauling) | 2.2 |
| First ionisation energy | 8.337 eV (804.4 kJ/mol) 2nd: 19.43 eV · 3rd: 32.93 eV |
| Electron affinity | 0.562 eV |
| Atomic radius (empirical) | 140 pm |
| Covalent radius | 120 pm |
| Van der Waals radius | 210 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 1,554.8 °C · 2,830.6 °F · 1,827.95 K |
| Boiling point | 2,963 °C · 5,365.4 °F · 3,236.15 K |
| Density | 12 g/cm³ |
| Specific heat capacity | 0.246 J/(g·K) |
| Thermal conductivity | 71.8 W/(m·K) |
| Crystal structure | Face-centred cubic |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 106Pd 27.33%, 108Pd 26.46%, 105Pd 22.33%, 110Pd 11.72%, 104Pd 11.14%, 102Pd 1.02% |
| Stable isotopes | 6 |
| Known isotopes | 42 |
| Abundance in Earth's crust | 0.015 mg/kg |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Palladium electron configuration
Palladium has 46 electrons. Written in short form, its ground-state configuration is [Kr] 4d10 — the electrons of the noble gas krypton, plus 4d10.Written out in full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10.
An exception to the filling rule. The simple aufbau (Madelung) order predicts 5s2, 4d8, but palladium actually has 5s0, 4d10. Half-filled and filled subshells, and the close energies of the outer orbitals, make this arrangement more stable.
Discovery and name
1802–1803 — William Hyde Wollaston · England.
The asteroid Pallas, discovered shortly before.
Known for
Used mainly in catalytic converters. Palladium can absorb up to about 900 times its own volume of hydrogen.
Isotopes of palladium
Naturally occurring palladium is a mix of 6 isotopes. Each has 46 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 106Pd | 46 | 60 | 27.33% | stable |
| 108Pd | 46 | 62 | 26.46% | stable |
| 105Pd | 46 | 59 | 22.33% | stable |
| 110Pd | 46 | 64 | 11.72% | stable |
| 104Pd | 46 | 58 | 11.14% | stable |
| 102Pd | 46 | 56 | 1.02% | stable |
42 isotopes of palladium are known in our data set (half-lives as published in nuclear data tables).
Palladium compared with group 10
The other elements in group 10, from top to bottom of the table:
| Element | Z | Atomic weight | Melting point | Boiling point | Density | Electronegativity |
|---|---|---|---|---|---|---|
| Nickel | 28 | 58.693 | 1,455 °C | 2,913 °C | 8.9 g/cm³ | 1.91 |
| Palladium | 46 | 106.42 | 1,555 °C | 2,963 °C | 12 g/cm³ | 2.2 |
| Platinum | 78 | 195.08 | 1,768 °C | 3,825 °C | 21.5 g/cm³ | 2.28 |
| Darmstadtium | 110 | [281] | — | — | 34.8 g/cm³ (pred.) | — |