Palladium Facts (Pd or Atomic Number 46)

Palladium Chemical & Physical Properties

Palladium is a soft silvery-white metal.
Palladium is a soft silvery-white metal. Tomihahndorf, wikipedia.org

Palladium is a silvery-white metallic element with atomic number 46 and element symbol Pd. In daily life, it's most often found in jewelry, dentistry, and catalytic converters for automobiles. Here is a collection of useful and interesting palladium facts:

Essential Palladium Facts

Atomic Number: 46

Symbol: Pd

Atomic Weight: 106.42

Discovery: William Hyde Wollaston 1802 (England) Wollaston noted his discovery of the metal in 1802 and offered the purified element for sale in 1803, although there was some controversy regarding the discovery. Richard Chenevix believed Wollaston's palladium to be a platinum-mercury alloy. Chenevix's palladium experiments earned him the 1803 Copley Medal, but it's clear Wollaston did at least partially purify the element. He dissolved platinum order from South America in aqua regia, neutralized it with sodium hydroxide and precipitated out the platinum. Reacting the remaining material with mercuric cyanide formed palladium(II) cyanide, which was heated to yield the purified element.

Word Origin: Palladium was named for the asteroid Pallas, which was discovered approximately the same time (1803). Pallas was the Greek goddess of wisdom.

Properties: Palladium has a melting point of 1554°C, boiling point of 2970°C, specific gravity of 12.02 (20°C), and valence of 2, 3, or 4. It is a steel-white metal which does not tarnish in air. Palladium has the lowest melting point and density of the platinum metals. Annealed palladium is soft and ductile, but it becomes much stronger and harder through coldworking. Palladium is attacked by nitric acid and sulfuric acid. At room temperature, the metal can absorb up to 900 times its own volume of hydrogen. Palladium can be beaten into leaf as thin as 1/250,000 of an inch.

Uses: Hydrogen readily diffuses through heated palladium, so this method is often used to purify the gas. Finely divided palladium is used as a catalyst for hydrogenation and dehydrogenation reactions. Palladium is used as an alloying agent and for making jewelry and in dentistry. White gold is an alloy of gold which has been decolorized by the addition of palladium. The metal is also used to make surgical instruments, electrical contacts, professional transverse flutes, and watches. In photography, palladium is an alternative to silver, used in the platinotype printing process.

Sources: Palladium is found with other metals of the platinum group and with nickel-copper deposits. The primary commercial sources are the Norilsk-Talnakh deposits in Siberia and the nickel-copper deposits of the Sudbury Basic in Ontario, Canada. Russia is the primary producer. It may be produced in a nuclear fission reactor from spent nuclear fuel.

Health Effects: Palladium, like the other platinum group metals, is mostly inert in the body as a bulk metal. However, there are reports of contact dermatitis, particularly in persons allergic to nickel. This causes problems when palladium is used in jewelry or dentistry. In addition to these uses, environmental exposure to palladium comes from release by automotive catalytic converters, food, and workplace exposure. Soluble compounds of palladium are excreted from the body within 3 days (99 percent). In mice, the median lethal dose of soluble palladium compounds (e.g., palladium chloride) is 200 mg/kg orally and 5 mg/kg intraveneously. Palladium is poorly absorbed and its toxicity is considered low, but it may be carcinogenic. Most plants tolerate it when it is present in low concentrations, although it is lethal to water hyacinth. Palladium serves no known biological role.

Currency: Palladium, gold, silver, and platinum are the only metals that have ISO currency codes. The codes for palladium are XPD and 964.

Cost: The price for palladium continues to rise. In 2016, palladium cost about $614 per ounce. In 2018, it reached $1100 per ounce.

Element Classification: Transition Metal

Palladium Physical Data

Density (g/cc): 12.02

Melting Point (K): 1825

Boiling Point (K): 3413

Appearance: silvery-white, soft, malleable and ductile metal

Atomic Radius (pm): 137

Atomic Volume (cc/mol): 8.9

Covalent Radius (pm): 128

Ionic Radius: 65 (+4e) 80 (+2e)

Specific Heat (@20°C J/g mol): 0.244

Fusion Heat (kJ/mol): 17.24

Evaporation Heat (kJ/mol): 372.4

Debye Temperature (K): 275.00

Pauling Negativity Number: 2.20

First Ionizing Energy (kJ/mol): 803.5

Oxidation States: 4, 2, 0

Lattice Structure: Face-Centered Cubic

Lattice Constant (Å): 3.890

Return to the Periodic Table

References

  • Hammond, C. R. (2004). "The Elements". Handbook of Chemistry and Physics (81st ed.). CRC press. ISBN 0-8493-0485-7.
  • Meija, J.; et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305
  • Wollaston, W. H. (1805). "On the Discovery of Palladium; With Observations on Other Substances Found with Platina". Philosophical Transactions of the Royal Society of London. 95: 316–330. doi:10.1098/rstl.1805.0024
  • Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.