Palladium is a chemical element with the atomic number 46 in the periodic table. It’s the most abundant platinum metal and occurs in Earth’s crust at an abundance of 0.015 parts per million. Being a member of the platinum group metals (PGM) of the periodic table, palladium has three valence electrons and adopts the oxidation states of +4, +2, and 0 when it becomes a part of a compound.
While palladium is considered to be relatively safe and non-toxic, its compounds are highly dangerous and may lead to serious health conditions. This precious metal is often used as a catalytic in the petrochemical and automotive industry.
Chemical and Physical Properties of Palladium
|Atomic weight (mass)||106.42 g.mol-1|
|Group number||10 (Transition Metal)|
|Color||A lustrous silvery-white metal|
|Physical state||Solid at 20°C|
|Half-life||From 10 milliseconds [>1.5 milliseconds] to 6.5 million years|
|Electronegativity according to Pauling||2.2|
|Melting point||1554.8°C, 2830.6°F, 1828 K|
|Boiling point||2963°C, 5365°F, 3236 K|
|Van der Waals radius||0.065 nm (+2)|
|Ionic radius||0.64 nm (+2)|
|Most characteristic isotope||106Pd|
|Electronic shell||[Kr] 4d10|
|The energy of the first ionization||703 kJ.mol-1|
|The energy of the second ionization||1870 kJ.mol-1|
|The energy of the third ionization||3177 kJ.mol-1|
|Uses||Used as a substitute for silver in dental items and jewelry. The pure metal is used as the delicate mainsprings in analog wristwatches. Also used in surgical instruments and as a catalyst.|
|Description||Silvery-ductile, and malleable metal|
|Crystal Structure||Cubic: Face centered|
|Covalent Radius||1.28 Å|
|Atomic Radius||1.79 Å|
|Atomic Volume||08.9 cm³/mol|
|Name Origin||Named after the asteroid, Pallas, discovered in 1803.|
|Discovery date||In 1803 by William Wollaston|
With the periodic table symbol Pd, atomic number 46, atomic mass of 106.42 g.mol-1, and electron configuration [Kr]4d10, palladium is a precious soft, ductile, and lustrous silvery-white metal with a face-centered cubic crystalline structure. Element 46 reaches its boiling point at 2963°C, 5365°F, 3236 K, while the melting point of palladium is achieved at 1554.8°C, 2830.6°F, 1828 K. This member of the platinum group metals in the periodic table has an electronegativity of 2.2 according to Pauling, whereas the atomic radius according to van der Waals is 0.065 nm (+2).
When exposed to air at room temperature, palladium is strongly resistant to corrosion. While element 46 is readily attacked by acid heated to high temperatures, it can be dissolved in aqua regia.
Palladium is soft and more ductile at higher temperatures, while lower temperatures make this element both harder and stronger. In addition, this chemical element does not tarnish when exposed to air, but it does lose the luster in moist environments that contain sulfur.
How Was Palladium Discovered?
During the 1700s, the Brazilian miners were familiar with a native alloy of palladium and gold, referred to as ‘ouro podre’, i.e. ‘worthless or rotten gold’. However, the palladium metal was not extracted until a century later.
In 1803, the English chemist William Hyde Wollaston (1766-1828) focused his scientific analysis on the residues left from platinum after it had been dissolved in aqua regia. When he provoked the chemical reaction between the platinum residue and the solution of nitric acid and hydrochloric acid, Wollaston managed to produce palladium cyanide. In the final step of his experiment, the English chemist heated the palladium compound which resulted in the extraction of the pure palladium metal.
William Hyde Wollaston announced the discovery of the new chemical element in a highly unusual way. Namely, instead of submitting the scientific evidence to the higher instances of the scientific world, Wollaston offered some quantity of the newly discovered metal for sale, describing its properties to anyone who was interested in buying it and advertising it as “the new silver”. Wollaston also offered a price to anyone who’ll be able to reproduce the substance. As could be expected, nobody ever got the prize.
However, a few years later he did reveal himself as the discoverer of palladium in front of the Royal Society of London after he finished his presentation of the scientific findings and evidence. Later, Wollaston claimed that the reason for not coming immediately upfront with his discovery was his intention to confirm the findings on the new element again by himself before putting his name on the discovery and in front of the scientific world.
How Did Palladium Get Its Name?
This chemical element is named after the asteroid Pallas, which is – in turn – named after the Greek goddess of wisdom, Pallas. The etymology of palladium leads to the Greek word ‘pallo’, meaning ‘the one who brandishes a spear’.
Where Can You Find Palladium?
The elemental form of palladium is rarely found in its pure form. However, this chemical element is one of the most abundant ones that occur in Earth’s crust along other chemical elements. It mostly occurs in sulfide minerals such as braggite.
For commercial purposes, palladium is often obtained as a by-product of the refining processes of copper and nickel ores. The majority of the world’s palladium supplies come from the United States, Australia, Russia, South Africa, Ethiopia, Canada, Brazil, and Colombia. These countries are considered to be the world’s leading producers of this precious metal.
List of Palladium Minerals
The following is a list of palladium-rich minerals:
- Cooperite (mineral)
Palladium in Everyday Life
The everyday use of palladium is versatile, especially regarding the industrial applications of element 46:
- Alloys made with palladium are often used in low voltage electrical contacts due to the high corrosion resistance of the element;
- Palladium’s hardness and durability are used for making of dental alloys (dental crowns
and bridges), multilayer ceramic capacitors, as well as in in printed-circuit components;
- In combination with rhodium, palladium is often used as a catalyst to convert pollutants like hydrocarbons, carbon monoxide, and nitrogen oxide in exhaust fumes to water, carbon dioxide, and nitrogen;
- The element 46 is often a substance of first choice in photography and technology, as well as in the manufacturing of watches, electrical contacts, and surgical instruments;
- As a catalyst, palladium also speeds heterogeneous catalytic processes like hydrogenation, dehydrogenation, and petroleum cracking;
- Palladium is also a key element for production of solar energy, as well as in fuel cells;
How Dangerous Is Palladium?
Despite being relatively safe as a substance, palladium compounds are considered to be highly toxic and carcinogenic. Also, occupational exposure to high levels of palladium in miners, dental technicians, and chemical workers may result in adverse health effects, such as Pd allergy, irritation of the respiratory tract and the eyes. Palladium chloride is especially toxic and may trigger kidney, liver, lymph nodes, adrenal gland, lungs, and bone marrow damage.
Environmental Effects of Palladium
In recent years, the analysis of air and dust samples show an increased environmental presence of palladium. According to the WHO, nearly 60% of European gasoline-fuelled cars sold in 1997, as well as many Japanese and US cars were equipped with palladium-containing catalytic converters. This type of exhaust system (mainly in diesel cars) has contributed immensely to an increased concentration of palladium in the air.
Isotopes of Palladium
Naturally occuring palladium is made up of six stable isotopes: palladium-102 (1.02% abundance), palladium-104 (11.14% abundance), palladium-105 (22.33% abundance), palladium-106 (27.33% abundance), palladium-108 (26.46% abundance), and palladium-110 (11.72% abundance).
With a half-life of 6.5 million years, palladium-107 is the most stable form of this chemical element. Electron capture is the primary decay mode of palladium before the most abundant stable isotope (palladium-106), while beta decay is the primary mode following this process.
Main isotopes of palladium (46Pd)
List of Palladium Compounds
Palladium can form organometallic compounds, but only few of these compounds have any industrial use. The element 46 has the strongest tendency among the other platinum metals to form a bond with carbon.
The compounds in which this member of the platinum group metals participates are mostly prepared with the oxidation state +4. However, palladium may also adopt the oxidation state of +2 and 0 in some compounds.
This chemical element readily reacts with hydrochloric, nitric, and sulfuric acid. These acids also slowly dissolve this precious metal.
The list of most commonly occurring palladium compounds contains the following items:
- (1,1′-Bis(diphenylphosphino)ferrocene)palladium(II) dichloride
- Allylpalladium chloride dimer
- Bis(acetonitrile)palladium dichloride
- Bis(benzonitrile)palladium dichloride
- Bis(triphenylphosphine)palladium chloride
- Compounds of palladium(III)
- Herrmann’s catalyst
- Lindlar catalyst
- Palladium dicyanide
- Palladium fluoride
- Palladium hydride
- Palladium tetrafluoride
- Palladium(II,IV) fluoride
- Palladium(II) acetate
- Palladium(II) bis(acetylacetonate)
- Palladium(II) bromide
- Palladium(II) chloride
- Palladium(II) fluoride
- Palladium(II) iodide
- Palladium(II) nitrate
- Palladium(II) oxide
- Sodium tetrachloropalladate
- Pyridine-enhanced precatalyst preparation stabilization and initiation (PEPPSI)
5 Interesting Facts and Explanations
- The platinum metals group of the periodic table is composed of the chemical elements rhodium, ruthenium, osmium, iridium, platinum, and palladium.
- Palladium exists in three states: Pd0 (metallic), Pd2+, and Pd4+.
- “White gold” is made when pure gold is alloyed with white metals such as nickel, silver, copper, manganese, zinc, and palladium. The metals added to gold in this alloy give the jewelry higher wear-resistance, durability, and strength. The finished product made of this yellow gold alloy is usually coated with rhodium, which produces an aesthetically pleasing luster. Nowadays, “white gold” is one of the most popular choices of customers in the jewelry industry. Currently, the price of palladium on the marketplace of precious metals is $2,675.07 per ounce.
- Palladium has the lowest melting point and is the least dense chemical of the platinum metals.
- Radiogenic Ag-107 is a decay product of Pd-107. It was first discovered in 1978, in the meteorite found in Santa Clara, Mexico.