Platinum

Lore & Background

Platinum is a lustrous, ductile, and malleable, silver-white metal. Platinum is more ductile than gold, silver or copper, thus being the most ductile of pure metals. Its physical characteristics and chemical stability make it useful for industrial applications. Its resistance to wear and tarnish is well suited to use in fine jewelry.

Platinum does not corrode, and bulk platinum does not oxidize in air at any temperature, but heated metal wires lose weight faster in air or oxygen than it does in a vacuum. The suggestion is that Pt forms a thin surface film that decomposes when heated above 500 °C. The most common oxidation states of platinum are +2 and +4. The +1 and +3 oxidation states are less common, and are often stabilized by metal bonding in bimetallic (or polymetallic) species.

Tetracoordinate platinum(II) compounds tend to adopt 16-electron square planar geometries. Although elemental platinum is generally unreactive, it is attacked by chlorine, bromine, iodine, and sulfur. It reacts vigorously with fluorine at 500 °C to form platinum tetrafluoride.

Platinum is insoluble in hydrochloric and nitric acid, but dissolves in hot aqua regia (a mixture of nitric and hydrochloric acids), to form aqueous chloroplatinic acid. As a soft acid, the Pt²⁺ ion has a great affinity for sulfide and sulfur ligands. Numerous DMSO complexes have been reported and care is taken in the choosing of reaction solvents. In 2007, the German scientist Gerhard Ertl won the Nobel Prize in Chemistry for determining the detailed molecular mechanisms of the catalytic oxidation of carbon monoxide over platinum (catalytic converter).

History & Scientific Recognition

Although pre-Columbian South American peoples crafted artifacts from platinum found in alluvial sands, European awareness of the metal remained limited to passing references in 16th-century writings. The element's name derives from the Spanish platina, a diminutive of plata (silver), reflecting its silvery-white appearance.

In the modern era, platinum's scientific importance has grown considerably. The element's six naturally occurring isotopes, including the NMR-active ¹⁹⁵Pt with its non-zero nuclear spin, have provided valuable tools in spectroscopy and isotope geology. Together, these contributions cement platinum's dual role as both a practical industrial material and a subject of fundamental scientific inquiry.

Physical & Chemical Properties

Platinum is a lustrous, silver-white transition metal that stands out for its extraordinary ductility, exceeding even gold, silver, and copper among pure metals. It is dense, malleable, and highly resistant to corrosion, earning its classification as a noble metal.

Its most common oxidation states are +2 and +4, with tetracoordinate platinum(II) compounds tending to adopt 16-electron square planar geometries. The metal resists hydrochloric and nitric acids individually but dissolves in hot aqua regia to yield chloroplatinic acid. As a soft acid, the Pt²⁺ ion exhibits a strong affinity for sulfide and sulfur ligands, a property that demands careful solvent selection in synthetic chemistry.

Rarity, Occurrence & Mining

Platinum is extraordinarily scarce in Earth's crust, occurring at a concentration of only about 5 micrograms per kilogram. This extreme rarity means barely a few hundred metric tonnes are produced globally each year, yet the metal's critical uses make it a highly valuable precious commodity. It is often found chemically uncombined as native platinum, particularly in alluvial river sands.

Pre-Columbian South American natives in Colombia's Chocó Department worked these deposits into artifacts long before European contact. Major geological sources include the Ural Mountains in Russia and the Sudbury Basin in Ontario, Canada, where the arsenide mineral sperrylite (PtAs₂) serves as a key platinum-bearing phase in nickel ores. In nickel and copper deposits, platinum-group metals also occur as sulfides, tellurides, antimonides, and end alloys.

Industrial & Medical Applications

Platinum's chemical inertness and resistance to wear make it indispensable across a remarkable range of industries. Beyond catalysis, platinum appears in laboratory equipment, electrical contacts, electrodes, platinum resistance thermometers, and dentistry. In the glass industry, molten glass does not wet platinum, making the metal ideal for manipulating it.

Its resistance to tarnish and wear suits fine jewelry perfectly. Perhaps most remarkably, platinum compounds such as cisplatin, oxaliplatin, and carboplatin serve as chemotherapy agents in the treatment of certain cancers, bridging the gap between inorganic chemistry and life-saving medicine. This versatility, spanning from automotive exhaust systems to oncology wards, underscores why such a scarce element commands such a premium price.

Reader's Guide

Platinum has six naturally occurring isotopes: ¹⁹⁰Pt, ¹⁹²Pt, ¹⁹⁴Pt, ¹⁹⁵Pt, ¹⁹⁶Pt, and ¹⁹⁸Pt. The most abundant of these is ¹⁹⁵Pt, comprising 33.83% of all platinum; it is the only stable isotope with a non-zero spin, of ½, and it is favorable for use in ¹⁹⁵Pt NMR. Due to its spin and large abundance, ¹⁹⁵Pt satellite peaks are also often observed in ³¹P and ¹⁹F NMR spectroscopy (e.g., for Pt-phosphine and Pt-alkyl complexes). The radioactive ¹⁹⁰Pt is the least abundant of these at only 0.012%; it undergoes alpha decay with a half-life of 4.83×10¹¹ years, causing the very low activity of 16.8 Bq/kg of natural platinum.

The decay of this isotope has some use in isotope geology, though not directly for dating. The other natural isotopes are theoretically capable of alpha decay also, but this has never been observed, and therefore they are considered stable. Platinum also has 38 synthetic isotopes ranging in atomic mass from 165 to 208, making the total number of known isotopes 44.

The most stable of these radioisotopes is ¹⁹³Pt, with a half-life of 50 years. Most platinum isotopes decay by some combination of beta decay and (on the proton-rich side) alpha decay. ¹⁸⁸Pt, ¹⁹¹Pt, and ¹⁹³Pt decay only by electron capture (besides the very small alpha branch of the first). ¹⁹⁰Pt and ¹⁹⁸Pt are predicted to have energetically favorable double beta decay paths. Platinum is an extremely rare metal on Earth, occurring at a concentration of only 0.005 ppm in Earth's crust. Platinum is often found chemically uncombined as native platinum and as alloy with the other platinum-group metals mostly.

Occurrence

Most often native platinum is found in secondary deposits among alluvial deposits. The alluvial deposits used by pre-Columbian people in the Chocó Department, Colombia are still a source for platinum-group metals. Another large alluvial deposit is in the Ural Mountains, Russia, and it is still mined.

In nickel and copper deposits, platinum-group metals occur as sulfides, tellurides, antimonides, and arsenides, and as end alloys with nickel or copper. Platinum arsenide, sperrylite (PtAs₂), is a major source of platinum associated with nickel ores in the Sudbury Basin deposit in Ontario, Canada. At Platinum, Alaska, about 17000 kg was mined between 1927 and 1975. The mine ceased operations in 1990.