Palladium
| General properties | |||||
|---|---|---|---|---|---|
| Name, symbol | Palladium, Pd | ||||
| Appearance | Silvery-white lustrous metal | ||||
| Palladium in the periodic table | |||||
| |||||
| Atomic number | 46 | ||||
| Standard atomic weight (Ar) | 106.42(1) | ||||
| Group, block | , d-block | ||||
| Period | period 5 | ||||
| Electron configuration | [Kr] 4d10 | ||||
per shell | 2, 8, 18, 18 | ||||
| Physical properties | |||||
| Silvery-white | |||||
| Phase | Solid | ||||
| Melting point | 1828.05 K (1554.9 °C, 2830.82 °F) | ||||
| Boiling point | 3236 K (2963 °C, 5365 °F) | ||||
| Density near r.t. | 12.023 g/cm3 | ||||
| when liquid, at | 10.38 g/cm3 | ||||
| Heat of fusion | 16.74 kJ/mol | ||||
| Heat of | 358 kJ/mol | ||||
| Molar heat capacity | 25.98 J/(mol·K) | ||||
| pressure | |||||
| Atomic properties | |||||
| Oxidation states | 0, +1, +2, +3, +4, +5, +6 (a mildly basic oxide) | ||||
| Electronegativity | Pauling scale: 2.20 | ||||
| energies |
1st: 804.4 kJ/mol 2nd: 1870 kJ/mol 3rd: 3177 kJ/mol | ||||
| Atomic radius | empirical: 137 pm | ||||
| Covalent radius | 139±6 pm | ||||
| Van der Waals radius | 163 pm | ||||
| Miscellanea | |||||
| Crystal structure | face-centered cubic (fcc) | ||||
| Speed of sound thin rod | 3070 m/s (at 20 °C) | ||||
| Thermal expansion | 11.8 µm/(m·K) (at 25 °C) | ||||
| Thermal conductivity | 71.8 W/(m·K) | ||||
| Electrical resistivity | 105.4 Ω·m (at 20 °C) | ||||
| Magnetic ordering | Paramagnetic | ||||
| Young's modulus | 121 GPa | ||||
| Shear modulus | 44 GPa | ||||
| Bulk modulus | 180 GPa | ||||
| Poisson ratio | 0.39 | ||||
| Mohs hardness | 4.75 | ||||
| Vickers hardness | 400–600 MPa | ||||
| Brinell hardness | 320–610 MPa | ||||
| CAS Registry Number | 7440-05-3 | ||||
| History | |||||
| Naming | after asteroid Pallas, itself named after Pallas Athena | ||||
| Discovery and first isolation | William Hyde Wollaston (1803) | ||||
Palladium is a chemical element with symbol Pd and atomic number 46. It is a platinum group metal, used mostly in electronics, though it shows promise in hydrogen storage.
Contents
Properties
Chemical
Palladium is much more reactive than the other platinum group metals. When heated to 800 °C, a black layer of palladium(II) oxide forms on the surface of the metal. Palladium dissolves slowly in concentrated nitric acid, in hot, concentrated sulfuric acid, and, when finely divided, in hydrochloric acid, to form their respective salts.
One of the most interesting properties of palladium is it's ability to absorb 900 times its own volume of hydrogen at standard ambient temperature and pressure. This property is intensely studied in hydrogen storage technologies, especially because it's simple, reversible and highly selective.
Physical
Palladium is a soft silver-white metal, with similar properties to platinum. It is the least dense (12.023 g/cm3) of the platinum group metals. Palladium melts at 1554.9 °C (the lowest melting point of the platinum group metals) and boils at 2963 °C. The metal is soft and ductile when annealed, but its strength and hardness increases when cold-worked.
Availability
Palladium is sold by various jewelers, usually as Pt/Pd alloy.
Certain monolithic ceramic capacitors contain palladium either alone, or as an alloy with silver, palladium, and with traces of nickel. The extraction process is quite complex, but a good method can be found on the indeedItdoes YT channel.
Palladium can also be extracted from catalytic convertors, where it is usually alloyed with platinum or rhodium, depending on the type of converter.
Palladium coins, such as the Soviet 25-rouble commemorative coin also contain palladium.
Isolation
Palladium can be extracted from various Pd/Pt alloys by dissolving them in nitric acid, followed by filtration to separate it from the platinum and reduction of the palladium salt to palladium metal.
It can also be extracted from certain monolithic ceramic capacitors, by dissolving them repeatedly in various acids and reducing it with various metals.
Projects
- Pd/C catalysts for hydrogenation
- Make palladium hydride
- Palladium(II) chloride synthesis
Handling
Safety
Bulk palladium is inert to most common chemicals and does not react with the human body, making it safe to use. Finely divided palladium metal can be pyrophoric and is considered a fire hazard.
Palladium salts however are quite toxic and should be handled with care.
Storage
Bulk palladium is inert and can be stored in any container. Powdered palladium is more reactive and should be stored in closed containers, away from flame sources.
Disposal
As palladium is expensive, it's better to try to recycle it than throwing it away.
