Platinum

Platinum
Atomic number	78
Symbol	Pt
Group	10 (transition metals)
Electronegativity	2.28 (Pauling)
Electron configuration	[Xe] 4f14 5d9 6s1
Density	21.45 g/cm^3
Period	6
Melting point	1768.3 °C
Phase STP	Solid
Block	d
Oxidation states	0, +2, +4
Wikidata	Q880

Platinum (symbol Pt, atomic number 78) is a dense, malleable transition metal and one of the six platinum-group elements (PGEs – Pt, Pd, Rh, Ru, Os, Ir) It has a silvery-white metallic luster and is remarkably inert (Platinum metal “is as resistant to corrosion as gold” At room temperature (20 °C) platinum is a solid (face-centered cubic crystal), with a high density around 21.45 g·cm^–3 (third-highest of all elements, after osmium and iridium). Its standard atomic mass is about 195.084 u In the periodic table Pt lies in group 10, period 6 (a d-block metal) Its most common oxidation states are +2 and +4 (though +1, +3, and even +5 are known in special compounds). Common abbreviations and identifiers include CAS 7440-06-4, but its chemical symbol “Pt” is widely used.

Electronic structure: Platinum atoms (atomic number 78) have electron shells filling to [Xe] 4f^14 5d^9 6s^1 In other words, the 6s and 5d shells contain 2 electrons short of being filled. The valence shell effectively has 5d^9 6s^1 (ten electrons available). The 5d electrons give Pt much of its chemistry. Being a heavy element, Pt has relatively high ionization energy and electronegativity. Its first ionization energy is about 865 kJ/mol (≈9.0 eV) and its electronegativity (Pauling scale) is ~2.2 larger than typical base metals. The atomic (nonbonded) radius of Pt is ~2.13 Å (213 pm) with a covalent radius about 1.30 Å In group 10 the trend is that atomic size increases and electronegativity roughly increases from Ni to Pd to Pt. For example, Pt’s Pauling EN (2.2) is higher than Ni’s (~1.91) and slightly above Pd’s (~2.20).

Key periodic trends: As a late transition metal, Pt’s properties fit the trends: it is large (radii of ~140–213 pm depending on definition fairly electronegative (2.2) and has high ionization energy (first IE ~864 kJ/mol Its filled 4f shell and shielded 6s/5d electrons make it compact relative to lighter metals. In metallic form Pt is diamagnetic (no unpaired electrons in the bulk), but some paramagnetic behavior can appear in complexes with unpaired d-electrons (e.g. Pt(III) species). The periodic trend of melting/boiling points is also high: Pt’s melting point is 1768 °C and boiling point ~3825 °C reflecting strong metallic bonding.

Isotopes and Nuclear Properties

Natural platinum consists of several isotopes. Five isotopes (^192Pt, ^194Pt, ^195Pt, ^196Pt, ^198Pt) are essentially stable and together make up almost all natural Pt, while a tiny fraction of ^190Pt (natural abundance ~0.01%) is very long-lived radioactive (undergoing alpha decay) Typical natural abundances are roughly 0.01% (^190Pt), 0.8% (^192Pt), 33% each of ^194Pt and ^195Pt, 25% ^196Pt, and about 7% ^198Pt The half-life of ^190Pt is on the order of 6×10^11 years so for most practical purposes all these isotopes can be treated as stable. ^186Pt also exists as trace radiogenic product.

Some platinum isotopes have special uses. In particular, the alpha decay of ^190Pt to ^186Os provides a geochronometer: the ^190Pt–^186Os system can date platinum ore deposits and related geological events (This decay is very slow, but measurable in ultrahigh-precision mass spectrometry.) Another important isotope is ^195Pt (abundance ~33.8%), which has nuclear spin 1/2 and is commonly used in NMR spectroscopy of platinum complexes (195Pt NMR gives detailed chemical-shift information No stable radioactive isotopes (like ^199Pt etc) are used in medicine, but radioactive ^191Pt and ^193Pt (artificially made) have been studied for radiotherapy. In reactor or accelerator production, ^191Pt (t½≈3 days) can be made as a branch from ^192Os.

There is no known biological or environmental role for platinum isotopes: Pt is so inert that virtually all biological Pt is incidental or from pollution. In the environment, Pt from catalytic converters appears in particulate form (e.g. Pt nanoparticles), but it is chemically inert and mostly accumulates in soil and dust with little evidence of bioaccumulation. In weathering processes some Pt can move in soluble chloroplatinate complexes under oxidizing and acidic conditions, but this is very limited.

Allotropes and Compounds

Platinum has no allotropes in the sense that carbon or sulfur do. The only form of Pt is the face-centered-cubic (FCC) metal. Unlike carbon (which has graphite/diamond) or sulfur (which has S8, S6, Spoly), platinum is always the same metallic crystal. The metal can appear as a lustrous ribbon, foil, or powder (“platinum black” – extremely fine powdered Pt used as catalyst support), but its crystal structure remains FCC.

Chemically, platinum forms a variety of compounds, typically with Pt in oxidation states 0 (metal), +2, and +4. Platinum(II) compounds often have square-planar geometry with d^8 configuration, while Pt(IV) compounds are usually octahedral (d^6). Some characteristic compounds include:

Halides: PtCl2 (platinum(II) chloride) is a yellow polymeric solid; PtBr2, PtI2 are analogues. Platinum(IV) halides include PtCl4 (brown solid) and PtBr4. A well-known complex is hexachloroplatinate: K2PtCl6 (with Pt(IV) in [PtCl6]^2-) or the acid H2PtCl6 (chloroplatinic acid) produced by dissolving Pt in aqua regia. PtF6 (platinum hexafluoride) is a powerful oxidizer (famous for oxidizing xenon).
Oxides: Platinum oxides are rare but include PtO (platinum(II) oxide, platinum black when reduced) and PtO2 (platinum(IV) dioxide), both black solids. PtO2 is used as a catalyst (e.g. in hydrogenation reactions) Platinum does not form stable hydroxides in water – it is not attacked by non-oxidizing acids due to its nobility.
Sulfides and minerals: In nature, platinum occurs in minerals like cooperite (PtS, also containing Fe) and sperrylite (PtAs2). These sulfide and arsenide minerals can contain large amounts of Pt along with other PGMs. Platinum metal can also alloy with other metals (Pt–Fe, Pt–Co, Pt–Ir alloys in magnetic materials).
Hydrides: No simple stable binary hydride PtH2 is known under normal conditions. However, Pt can adsorb hydrogen on its surface and form complex hydrides (e.g. PtCl2(H2)2, a dihydrogen complex). Under high pressure, platinum hydride has been synthesized.
Organometallics and complexes: Pt readily forms coordination complexes. A famous example is cisplatin (cis-[Pt(NH3)2Cl2, a square-planar Pt(II) complex used in chemotherapy. Platinum also forms compounds like Zeise’s salt [PtCl3(C2H4^- and many others with organic ligands (Pt–carbon bonds, Pt–H bonds, etc). Pt(II) has a strong affinity for soft ligands (Cl^-, Br^-, PR3, NR3), while Pt(IV) can form octahedral species with F^-, OH^-, and others.
Chloroplatinic acid: A key compound in industry is H2PtCl6 (aq), hexachloroplatinic acid, obtained by dissolving Pt in hot HCl + HNO3 (aqua regia). This yellowish solution contains the [PtCl6]^2- anion (Pt(IV) complex). Reduction of H2PtCl6 (e.g. with H2) yields pure platinum powder.

Overall, platinum’s compounds are dominated by Pt(II) and Pt(IV) coordination chemistry, with characteristic square-planar complexes (Pt(II)) and octahedral complexes (Pt(IV)). Because Pt is relatively inert to oxygen and water, many Pt compounds must be synthesized under special conditions (strong oxidizers, halogens, or by ligand substitution).

Physical Properties

Platinum is a heavy metal with high thermal and electrical conductivity. Its density is about 21.5 g·cm^–3 at STP The melting point is around 1768 °C (2041 K) and boiling point about 3825 °C (4098 K) – among the highest of all elements. At room temperature it is a ductile, malleable metal (it can be drawn into wire or beaten into foil) with a shiny silvery-white surface The face-centered cubic unit cell has a lattice constant of about 3.92 Å (0.392 nm) and typically 4 atoms per cell.

Electrical Conductivity: Platinum is a good conductor, though not as high as copper. Its electrical resistivity is about 105 × 10^–9 Ω·m (at 20 °C) (For comparison, copper’s resistivity is ~17 nΩ·m.) Thus its conductivity is on the order of 1×10^7 S/m. In industry, Pt is often used for electrical contacts and electrodes because it resists corrosion.
Thermal Conductivity: The thermal conductivity of solid platinum is ≈72 W·m^–1·K^–1 at room temperature This is lower than for copper (~400 W/m·K) or silver, but still quite high. Platinum is often used in high-temperature equipment (furnace elements, crucibles) partly because it can conduct heat and load without oxidizing.
Crystal Structure and Magnetism: As noted, Pt metal is FCC. It is paramagnetic when alloyed or under some conditions, but pure crystalline platinum is usually described as Pauli paramagnetic (very weak magnetization under external field) due to its conduction electrons. Unlike iron or nickel, Pt is not ferromagnetic. Many platinum alloys (with 2–10% Co or Fe) are used as high-performance magnets, exploiting exchange interactions, but pure Pt itself has no permanent magnetism.
Spectroscopy: Platinum atoms have many electronic transitions, but these are mostly in the ultraviolet. In practice, Pt spectroscopy refers often to X-ray lines (e.g. Pt Lα ~9.44 keV) or to analysis of Pt nanoparticles (surface plasmon features). There are no strong convenient optical emission lines of atomic Pt in the visible for general use.

Spectroscopically, Pt can be detected by flame atomic emission (a few lines around 265–283 nm and 340–360 nm), atomic absorption, or by X-ray fluorescence in analytical chemistry. But such details are specialized. The key fact is that platinum metal is very lustrous (silvery) and does not change color or corrode in air even at high temperatures.

Chemical Reactivity and Trends

Nobility: Platinum is one of the “noble metals” – it is extremely unreactive towards oxygen, water, and most acids at room temperature. It does not oxidize in air, even when heated (no tarnish) It is only attacked by hot strong oxidizing agents. For example, concentrated nitric acid or sulfuric acid alone have little effect, but aqua regia (1:3 HNO3:HCl) dissolves Pt by converting it to chloroplatinic acid (H2PtCl6) and chloronitrosyl species. The action of aqua regia can be summarized:

Pt + 4 HNO3 + 6 HCl → H2PtCl6 + 4 NO2 + 4 H2O.

Aqua regia oxidizes Pt to Pt(IV) and yields the soluble [PtCl6]^2– complex. Solutions of Pt(IV) can often be reduced chemically or by electrolysis back to Pt metal.

Redox behavior: Platinum as a metal is Pt^0 (oxidation state 0). In compounds, Pt^2+ and Pt^4+ are the most stable. Pt(II) is a moderate oxidizing agent (PtCl2 is stable in air). Pt(IV) compounds are stronger oxidizers (e.g. Pt(IV) oxide or chlorides can oxidize HX to X2). Pt(IV) can often be reduced to Pt(II) by mild reagents. For example, PtO2 + H2/ethanol → Pt + water. In general, Pt^4+ → Pt^2+ requires a reducing agent (e.g. hydrogen or sulfite).

Complexation: Platinum forms very stable complex ions. Chloride complexes of Pt are famous: [PtCl6]^2– (yellow) and [PtCl4]^2– (dark), often as K2PtCl6 or K2PtCl4 salts. It also forms ammonia complexes, e.g. [Pt(NH3)4]^2+. In biology/medicine, common Pt drugs like cisplatin are Pt(II) square-planar amines. Pt(IV) also forms chelate rings (e.g. K2[PtCl6. Soft bases (S^2–, CN^–, PR3, etc.) bind strongly to Pt(II). Pt behaves as a Lewis acid in complexes, typically achieving an 18-electron noble gas configuration around Pt(II) or Pt(IV).

Acid-base reactions: Platinum hydroxides/hydroxyls are not encountered because Pt does not dissolve in ordinary bases or weak acids. Hot concentrated KOH can oxidize Pt somewhat (forming species like K2[Pt(OH)6 but this is not common. Platinum surfaces are inert in acid or base unless strong oxidants are present.

Catalytic behavior: A hallmark of platinum is its catalytic activity when finely divided or supported. Platinum metal catalyzes countless reactions: it adsorbs hydrogen (to form surface Pt–H), oxygen, and organics, facilitating their reaction. It is an excellent hydrogenation catalyst (e.g. alkene to alkane), oxidation catalyst (CO to CO2, NO to N2), and dehydrogenation catalyst. In automobile three-way catalysts, platinum (often with palladium and rhodium) converts CO, NO, and hydrocarbons into CO2, N2 and H2O In many laboratory hydrosilylation or hydrogenation reactions, Pt black or supported Pt is used It also serves as an inert electrode in electrochemistry (e.g. as a standard hydrogen electrode).

Corrosion and passivation: Unlike iron or copper, platinum does not form a protective oxide that then traps more corrosion – it is already so unreactive that it stays shiny in most media. It is effectively permanently passivated by nature. In strong oxidizing environments platinum can form a thin oxide film (PtO2) at high temperature, but this is stable and protective. In plain air and water at any temperature up to white heat, Pt will not corrode

In summary, Pt’s reactivity is extremely low: it sits well below hydrogen in the metal reactivity series. Only aggressive oxidizers (Cl2, F2, hot aqua regia, hot alkali fusion) can convert it into soluble salts. Otherwise it behaves as a noble, inert metal.

Occurrence and Production

Platinum is very rare in the Earth’s crust (on the order of 5–10 parts per billion) and is found only sporadically. It generally occurs alloyed or uncombined in ores, never as a simple “oxide ore” like iron or aluminum. The most important occurrences are:

Alluvial deposits: Platinum is found as small grains in streambeds (placer deposits) along with gold and other dense minerals. Ancient peoples in South America and Asia mined some of these naturally occurring Pt grains for ornamental use.
Sulfide ores: Most commercial platinum comes from sulfide ores in igneous intrusions. The chief source is the Bushveld Igneous Complex in South Africa, where layers like the Merensky Reef and UG2 Reef contain dispersed platinum-group minerals (PGMs). Common platinum minerals there include cooperite (PtS) and various platinum–iron alloys. South Africa alone holds the vast majority of the world’s known platinum reserves (nearly 90%) and in 2022 produced roughly 66% of the world’s mined platinum
Other ores: Russia (Norilsk region) has abundant Ni-Cu sulfide deposits with PGMs and is the world’s second-largest producer Other producers include Zimbabwe (Great Dyke), Canada (Sudbury and other Ni mines) and the United States (still producing in Montana and recycling from catalysts). These deposits are mined primarily for nickel and copper, with platinum and other PGMs as by-products.
Nickel–Copper sulfides: Platinoids are often extracted during processing of Ni–Cu sulfide ores. For instance, ores from Sudbury (Canada) and Norilsk (Russia) yield platinum as a by-product of nickel and copper refining.
Recycling: A significant fraction of platinum supply comes from recycling. Automobile catalysts, industrial catalysts, and scrap jewelry are recovered and refined to reclaim Pt. About 20–30% of annual platinum supply is from recycled sources.

Key producers (2022 data) were South Africa (~140,000 kg Pt), Russia (~20,000 kg), Zimbabwe (~15,000 kg), followed by Canada and the USA at a few thousand kg Proven global platinum reserves were ~71,000 tonnes (2022 estimate), overwhelmingly in South Africa (the remainder mainly in Russia, Zimbabwe, and North America). In summary, platinum is scarce: its abundance is measured in parts-per-billion in the crust, and the supply comes from a few large geologic deposits and extensive recycling.

Applications and Technology

Platinum’s unique combination of inertness, catalytic activity, and high-temperature stability gives it a wide range of vital applications. By far the largest use is heterogeneous catalysis. About half or more of platinum mined each year goes into autocatalysts for vehicles In catalytic converters, platinum promotes oxidation of carbon monoxide and hydrocarbons into CO2 and water, and reduction of NOx to N2. Platinum is also crucial in fuel-cell technology (especially proton-exchange membrane fuel cells) where it catalyzes both the hydrogen-oxidation reaction at the anode and the oxygen-reduction reaction at the cathode (The scarcity of Pt in fuel cells is a major technical challenge; research into Pt-based alloys and non-PGM catalysts is intense.)

In the chemical industry platinum catalysts accelerate many processes. For example, Pt catalysts are used in the Ostwald process (ammonia oxidation to nitric acid) and in devices that make silicone polymers and benzene by catalytic reforming. Fine chemical production and laboratory chemistry often rely on Pt catalysts for hydrogenations and dehydrogenations of organic compounds.

Besides catalysts, platinum is valued in electronics and materials: its high conductivity and stability make it ideal for electrical contacts, thermocouples, and resistance temperature sensors. Thin films of Pt are used in hard-disk drives and multi-layer ceramic electronic devices. In fiber optics and LCD manufacturing, Pt wires and sputter targets are used for drawing glass and for depositing transparent conductors. Platinum chemicals (like Pt(IV) oxide) coat glass furnace inserts or UV lamps to improve durability. Because Pt remains stable at high temperatures, it is used for crucibles, electrodes, and heat-exchangers in chemistry and metallurgy.

As a jewelry metal, platinum is prized for its luster and hypoallergenic qualities. It does not discolor (even under skin) and is dense and malleable, making it good for fine jewelry (rings, necklaces, watches). Although demand for Pt jewelry is smaller than for gold or silver, it is significant – around 5–10% of annual platinum use Investment coins and bullion bars are also made from platinum (though PT prices tend to be volatile and lower than gold).

In medicine, platinum compounds have a unique role. The chemotherapy drug cisplatin (cis-Pt(NH3)2Cl2) and related Pt(II) or Pt(IV) complexes are important cancer treatments (particularly for testicular, ovarian, bladder cancers) These drugs work by binding to DNA in tumor cells and disrupting cell division. Platinum metal itself is biocompatible and benign, so platinum is used for certain medical implants and devices (e.g. pacemaker electrodes, surgical instruments, dental alloys) where corrosion-resistance is needed

Additional uses include laboratory standards: the International Prototype Kilogram (prior to 2019) was made of a 90%-10% platinum–iridium alloy highlighting Pt’s dimensional stability. Platinum wires are used in catalytic platinum–platinic oxide (PtO2) electrodes for pH and standard hydrogen electrodes. Even in hydrogen fueled aerospace, platinum can catalyze hydrogen–oxygen reactions safely.

Representative industries:

Automotive: catalytic converters (platinum-group catalysts) as well as spark plugs.
Petrochemical: reforming and hydrogenation catalysts.
Glass & Fibers: Pt-rhodium electrodes and filaments.
Electronics: resistive sensors, hard-disc platters.
Fine chemicals: chromatography columns (Pt columns), catalysts.
Medical: oncology drugs, surgical tools.
Jewelry & Finance: rings, investment coins.

Virtually every modern economy relies on platinum in tiny but critical ways, often behind the scenes. Its scarcity and cost (often hundreds of dollars per troy ounce) makes it a strategic material.

Biology, Environment, and Safety

Biologically, platinum has no known essential role The human body does not use Pt in any metabolic process, and most platinum salts are toxic rather than beneficial. Elemental platinum is inert; metallic Pt in most forms is essentially nontoxic (it passes through the body largely unchanged) However, many platinum compounds are hazardous. Soluble Pt salts (chlorides, amines, sulfides) can cause skin irritation, allergic dermatitis, and respiratory sensitization (a major concern in catalyst production facilities). Occupational exposure to fine platinum metal powder or soluble salts can induce “platinum salts asthma” in sensitized workers The most notorious toxic Pt compounds are those used in chemotherapy (cisplatin, carboplatin); these are intentionally toxic to cancer cells but also damage healthy tissues (notably kidneys, nerves)—necessitating careful clinical monitoring.

Environmentally, platinum particles accumulate slowly. The emission of Pt-group metals from automobile catalysts has been detected in urban dust and soils near highways. These microparticles are relatively inert (Pt metals do not dissolve in rain), but trace Pt ions can leach under extreme acid. At present, platinum is not considered a major pollutant, though studies continue on the long-term effects of dispersed catalyst residues.

In terms of regulatory safety, agencies classify platinum metal itself as relatively low-hazard (NIOSH REL for platinum metal dust is 1 mg/m^3 (as dust) and OSHA PEL is 15 mg/m^3 These limits are primarily to prevent obstructive lung effects from metal dust. However, for soluble platinum salts, exposure limits are much lower due to allergy risk. In practice, handling platinum metal simply requires routine metal safety (avoid fine dust, use fume hoods when dissolving, wear gloves). Disposal of platinum-containing waste is carefully controlled because of both toxicity and its value (often recycled). Overall, platinum’s high value and stability mean it is more often a matter of economics than toxicity – the main safety issues arise when preparing or using reactive Pt compounds (e.g. mixing aqua regia, handling cisplatin).

History and Etymology

Platinum has a long and colorful history. Its name comes from the Spanish word platina (“little silver”) Early Spanish colonial miners in what is now Colombia in the 16th–17th centuries encountered platinum grains in gold placers. Not recognizing it as a distinct metal, they considered it an impurity – “platina del Pinto” (little silver from the Pinto River) – and tossed it aside. Indigenous peoples of South America, however, had been using platinum in jewelry and ornaments for millennia

The first European mention of platinum appears around 1557 by Julius Caesar Scaliger, who described a metal that would not melt in gold fires. But platinum did not enter European science until the 18th century. In 1735 the Spanish naval officer Antonio de Ulloa reported a new “white metal” from South America to the Royal Society of London Shortly thereafter, by the 1750s, European scientists (including Engelhard in Germany and Black in England) described platinum’s properties. In 1759 Scipione del Ferro named it “platinum” after the Spanish term By the early 19th century, researchers like William Wollaston separated platinum from iridium and other impurities, and recognized it as a pure element.

A milestone in platinum’s history was its use in metrology: after 1799 the Kilogram was defined by a platinum (and later platinum–iridium) prototype block The metal’s rarity and resistance made these artifacts stable references. In the 20th century, platinum’s catalytic properties were discovered and rapidly exploited (e.g. in contact process and later in automotive catalysts). The chemotherapy drug cisplatin, discovered in 1965 (Rosenberg et al.), marked another landmark: Pt went from inert metal to life-saving medicine. Cultural references also persist (e.g. “platinum records” in music signify sales success, derived from awarding platinum jewelry).

The official chemical symbol Pt was first used by Chemists around 1800. The origin of the name and symbol are fully consistent with the Spanish origin (plata means silver, platin “little silver”). Discoveries of new platinum-group elements (iridium, osmium, rhodium, ruthenium, palladium) in the early 1800s were partly due to studying platinum ores. Today, platinum mining and refining is a key industry in South Africa and Russia, and new technological applications (fuel cells, nanocatalysts, advanced alloys) continue to highlight platinum’s unique status.

Data Table

Property	Value for Platinum (Pt)
Atomic number (Z)	78
Symbol	Pt
Group / Period / Block	10 / 6 / d-block
Standard state (20 °C)	Solid (metal)
Atomic weight	195.084 u (standard atomic weight)
Electron configuration	[Xe] 4f^14 5d^9 6s^1
Valence electrons	5d^9 6s^1 (two electrons unfilled)
Common oxidation states	+2, +4 (also +1, +3 in some complexes)
Atomic radius	~213 pm (nonbonded)
Covalent radius	~130 pm
First ionisation energy	8.92 eV (864 kJ/mol)
Electronegativity (Pauling)	2.28
Density	21.45 g/cm^3 (at 20 °C)
Melting point	1768 °C (2041 K)
Boiling point	3825 °C (4098 K)

Each value above is taken from authoritative sources (see references) or widely accepted data for platinum. The isotope abundances sum to 100% and ^190Pt’s long half-life indicates nearly stable behavior in nature. The table highlights platinum’s key identifiers (symbol, Z, electron config) and major thermophysical properties.