Platinum is a heavy element mainly synthesized by the r-process (rapid neutron capture) during violent events such as supernovae and neutron star mergers. It is a siderophile element, with a strong affinity for metallic iron. This geochemical trait explains why, during Earth's formation, most of the platinum in primordial matter migrated to the metallic core. The extremely low concentration of platinum in the mantle and Earth's crust (parts per billion) contrasts with its relative abundance in chondritic meteorites, which better reflect the composition of the nascent solar system.
The cosmic abundance of platinum is about 1.5×10⁻¹² times that of hydrogen in number of atoms, making it slightly more abundant than gold but much rarer than silver or palladium. In meteorites, the abundance ratios between platinum and other siderophile elements (such as iridium, osmium, ruthenium) are used as "fingerprints" to classify meteorite types and understand planetary accretion processes.
Like iridium, platinum is a key tracer of extraterrestrial material in geological layers. Platinum anomalies are sought in sedimentary strata to identify past asteroid impacts. The platinum-osmium isotopic system (\(^{190}\mathrm{Pt}\) decays to \(^{186}\mathrm{Os}\)) is a complementary dating tool to the Re-Os system, used to date very ancient planetary differentiation events or to study the source of platinum in terrestrial deposits.
Spectral lines of platinum have been detected in the atmospheres of some metal-rich stars, providing information on nucleosynthesis processes. In the interstellar medium, platinum is probably present in the form of refractory dust grains, similar to those that may have been incorporated into planets during their formation.
The name "platinum" comes from the Spanish "platina", a diminutive of "plata" meaning silver. This term was used somewhat pejoratively by Spanish conquistadors in the 16th century, who found this white metal mixed with gold in Colombian rivers and considered it "little silver" or "impure gold," sometimes discarding it. Its true value was only recognized later.
Artifacts made of gold-platinum alloy dating from the pre-Columbian era have been found in Ecuador, attesting to the ancient mastery of the metal by indigenous peoples. For European science, platinum was formally identified as a new element in the 1740s-1750s, notably through the work of the Spanish scholar Antonio de Ulloa (who brought it from America) and the British scientist William Brownrigg. The Swedish chemist Henrik Scheffer published a detailed description in 1752, calling it "white gold."
Purifying platinum was a major challenge due to its extremely high melting point. The first method, developed in the 1780s by the Frenchman Pierre-François Chabaneau under the patronage of the King of Spain, involved purifying platinum sponge by hammering and hot forging. The "fire assay" technique made it possible to produce the first malleable ingot. In the 19th century, the discovery of other platinum group metals (palladium, rhodium, etc.) in raw platinum and the development of hydrogen-oxygen furnaces by Henri Sainte-Claire Deville and Jules Henri Debray (1857) paved the way for industrial production.
The main platinum deposits are of two types:
Global annual production is about 180-200 tons. South Africa dominates production (≈70%), followed by Russia (≈20%). Platinum is one of the most expensive metals, generally more valuable than gold except during periods of high gold demand. Its value is driven by critical industrial applications, far beyond jewelry.
Platinum (symbol Pt, atomic number 78) is a transition metal of the 6th period, located in group 10 (formerly VIII) of the periodic table, along with nickel, palladium, and darmstadtium. It is the leader of the six platinum group metals (PGM). Its atom has 78 protons, usually 117 neutrons (for the stable isotope \(^{195}\mathrm{Pt}\)), and 78 electrons with the electronic configuration [Xe] 4f¹⁴ 5d⁹ 6s¹. This particular configuration (5d⁹ 6s¹ instead of the expected 5d⁸ 6s²) results from increased stability of half-filled subshells.
Platinum is a precious metal, silvery-white, lustrous, very dense, malleable, ductile, and relatively soft in its pure state.
Platinum crystallizes in a face-centered cubic (FCC) structure.
Platinum melts at 1768.3°C (2041.4 K) and boils at 3825°C (4098 K). Its wide solid temperature range and excellent chemical stability at high temperatures make it a material of choice for high-temperature equipment.
Platinum is the archetype of the noble metal. It is resistant to most chemical agents:
Density: 21.45 g/cm³.
Melting point: 2041.4 K (1768.3°C).
Boiling point: 4098 K (3825°C).
Crystal structure: Face-centered cubic (FCC).
Electronic configuration: [Xe] 4f¹⁴ 5d⁹ 6s¹.
Main oxidation states: +2 and +4.
| Isotope / Notation | Protons (Z) | Neutrons (N) | Atomic mass (u) | Natural abundance | Half-life / Stability | Decay / Remarks |
|---|---|---|---|---|---|---|
| Platinum-190 — \(^{190}\mathrm{Pt}\) | 78 | 112 | 189.959932 u | ≈ 0.012% | 6.5×10¹¹ years | Alpha radioactive with extremely long half-life. Decays to \(^{186}\mathrm{Os}\). Considered stable for usual applications. |
| Platinum-192 — \(^{192}\mathrm{Pt}\) | 78 | 114 | 191.961038 u | ≈ 0.782% | Stable | Stable isotope. |
| Platinum-194 — \(^{194}\mathrm{Pt}\) | 78 | 116 | 193.962680 u | ≈ 32.967% | Stable | Stable isotope, one of the most abundant. |
| Platinum-195 — \(^{195}\mathrm{Pt}\) | 78 | 117 | 194.964791 u | ≈ 33.832% | Stable | Stable and major isotope. The only natural isotope with non-zero nuclear spin (I=1/2), making it active in \(^{195}\mathrm{Pt}\) Nuclear Magnetic Resonance (NMR). |
| Platinum-196 — \(^{196}\mathrm{Pt}\) | 78 | 118 | 195.964952 u | ≈ 25.242% | Stable | Stable isotope, very abundant. |
| Platinum-198 — \(^{198}\mathrm{Pt}\) | 78 | 120 | 197.967893 u | ≈ 7.163% | Stable | Stable isotope. |
N.B.:
Electron shells: How electrons are organized around the nucleus.
Platinum has 78 electrons distributed over six electron shells. Its electronic configuration [Xe] 4f¹⁴ 5d⁹ 6s¹ is an exception to simple filling rules. It can also be written as: K(2) L(8) M(18) N(32) O(17) P(1), or in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d⁹ 6s¹. The 5d subshell is one electron short of being complete.
K shell (n=1): 2 electrons (1s²).
L shell (n=2): 8 electrons (2s² 2p⁶).
M shell (n=3): 18 electrons (3s² 3p⁶ 3d¹⁰).
N shell (n=4): 32 electrons (4s² 4p⁶ 4d¹⁰ 4f¹⁴).
O shell (n=5): 17 electrons (5s² 5p⁶ 5d⁹).
P shell (n=6): 1 electron (6s¹).
Platinum has 10 valence electrons if we count the electrons in the 5d and 6s shells (9+1). It exhibits rich chemistry with several stable oxidation states, the most important being +2 and +4. The +2 state (d⁸ configuration) is very common in square planar complexes, such as the famous cisplatin (cis-[PtCl₂(NH₃)₂]), an anticancer drug. The +4 state (d⁶ configuration) is also stable (e.g., PtO₂, PtF₆). Other states such as 0, +1, +3, +5, and +6 exist but are less common.
The coordination chemistry of platinum is vast and of paramount importance, both in catalysis and medicine. Its tendency to form square planar complexes with "soft" ligands (such as phosphines, thioethers) and its ability to catalyze hydrogenation, oxidation, and coupling reactions make it a central metal in organometallic and industrial chemistry.
Platinum is perfectly stable in air at all temperatures. It does not form stable oxide under normal conditions. A PtO₂ oxide can form at high temperature under high oxygen pressure, but it decomposes around 450°C. On the surface, it can form a thin oxide layer that contributes to certain catalytic properties.
Platinum is unaffected by water and simple mineral acids, even when concentrated and boiling. This inertness is the basis for its use in laboratory utensils (crucibles, dishes) and chemical equipment.
Its only notable weakness is aqua regia, a mixture of concentrated nitric and hydrochloric acids, which dissolves it to form hexachloroplatinic acid (IV), H₂[PtCl₆]: Pt + 4 HNO₃ + 6 HCl → H₂[PtCl₆] + 4 NO₂ + 4 H₂O. This compound is the starting point for the preparation of most other platinum compounds.
N.B.:
This is the largest industrial application of platinum (about 30-40% of annual demand). The catalytic converter converts harmful exhaust gases into less dangerous compounds:
Platinum (often combined with palladium and rhodium) is dispersed as nanoparticles on a ceramic honeycomb support. Its efficiency and durability at high temperatures are unmatched. Global antipollution standards (Euro, EPA) make this material indispensable.
Platinum is a prestigious jewelry metal, appreciated for:
It is mainly used for wedding rings, solitaires, high-end watches, and diamond settings (its neutral white perfectly enhances the stone).
Beyond the catalytic converter, platinum catalyzes fundamental reactions:
Square planar platinum(II) complexes are a major class of chemotherapies:
These drugs save hundreds of thousands of lives each year.
Platinum is a critical material for the energy transition:
Metallic platinum is inert and non-toxic. This is why it is used in jewelry and dentistry without risk. However:
Platinum mining generates large amounts of waste rock and tailings and can have local impacts on water and soil quality. Platinum from used catalytic converters can end up as fine particles in road dust and roadside soils, but at measured concentrations, its direct ecological impact is considered low. Research continues to assess the long-term fate and effects of these particles.
Platinum recycling is highly economically attractive and crucial for supply security. The main sources are:
The overall recycling rate is estimated at about 25-30% of demand, but it could be significantly improved with better collection systems. South Africa has set up infrastructure to recycle a large part of its catalytic waste.
Platinum is a critical material for the modern economy, with a geographically concentrated supply chain (South Africa). The challenges are:
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