Ruthenium
| Ruthenium | |
|---|---|
| |
| Atomic number | 44 |
| Symbol | Ru |
| Group | 8 |
| Electronegativity | 2.2 (Pauling) |
| Electron configuration | [Kr] 4d7 5s1 |
| Density | 12.37 g/cm^3 |
| Period | 5 |
| Melting point | 2334 °C |
| Phase STP | Solid |
| Block | d |
| Oxidation states | +2, +3, +4 |
| Wikidata | Q1086 |
Ruthenium (chemical symbol Ru, atomic number 44) is a rare, silvery-white metal in the platinum group of the periodic table. It is hard and corrosion-resistant, combining many of the noble properties of platinum and palladium. Small amounts of ruthenium greatly increase the hardness and wear resistance of platinum or palladium alloys, making it valuable in electrical contacts and jewelry. Ruthenium and its compounds also find use in catalysis (for example in ammonia and acetic acid production) and in electronics: ruthenium oxide coatings on titanium anodes (RuO₂/Ti anodes) support chlorine and oxygen evolution, and ruthenium is used in chip resistors and as a thin-film layer in microelectronics. Despite its industrial importance, ruthenium is very scarce in nature.
Overview and Key Facts
- Symbol and Atomic Number: Ru, 44.
- Category: Transition metal (platinum group metal).
- Group/Period/Block: Group 8, Period 5, d-block. (Group 8 is the iron–ruthenium–osmium column.)
- Standard State: Solid at 20 °C; it is a hard lustrous white metal.
- Atomic Weight: about 101.07 (standard atomic mass).
- Electron Configuration: [Kr]4d^7 5s^1. (Ruthenium has eight valence electrons beyond krypton: one 5s and seven 4d.)
- Common Oxidation States: +2, +3, +4 are most prevalent; other states include 0, +6, +8 (in RuO₄), and a rare −2 in certain complex anions.
- Isotopes: There are seven naturally occurring isotopes (mass numbers 99–104, with ^102Ru the most abundant at about 31.6%). No radioisotope is stable, but six of the seven are effectively stable (the lightest, ^96Ru, double–beta decays with an extremely long half-life).
Ruthenium shares many traits with its platinum-group neighbors. It is denser and has a higher melting point than most transition metals, but does not tarnish or corrode in air at room temperature. In bulk it forms metallic crystals (the stable form is hexagonal close-packed). In the periodic table, ruthenium follows technetium and precedes rhodium. It does not occur as a free metal in appreciable amounts but is a trace component of platinum ores and certain nickel and copper ores.
Atomic Structure and Electron Configuration
Ruthenium’s [Kr]4d^7 5s^1 electron configuration means it has one 5s electron and seven 4d electrons outside the krypton core. The eight valence electrons allow ruthenium to exhibit multiple oxidation states. The filled 4p^6 and 4s^2 shells of krypton are inner core electrons, making ruthenium much heavier and larger than first-row transition metals.
Compared with its group neighbors (iron above and osmium below), ruthenium’s atomic radius and ionization energy reflect its position in the 4d series. Its covalent radius is about 1.34 ångströms (Å), somewhat larger than iron’s (1.26 Å) but similar to osmium’s (1.35 Å), due to the “lanthanide contraction” effect on 5d elements. The first ionization energy of Ru (~710 kJ/mol, or 7.36 eV) is slightly lower than iron’s (762 kJ/mol) but lower than osmium’s (~840 kJ/mol); this indicates ruthenium’s outer 5s electron is less tightly bound than iron’s 4s electron. On the Pauling electronegativity scale, Ru is about 2.2, higher than iron (1.83) and comparable to osmium (~2.2). This moderately high electronegativity corresponds to Ru’s tendency to hold onto electrons and not act as a strong reducing agent.
Across the periodic table, ruthenium fits the trends for 4d transition metals: its atomic radius is larger than 3d metals above it, its ionization energy is moderate, and it is less reactive than mid-series 4d metals like technetium or molybdenum. Its magnetic properties at room temperature are paramagnetic (no permanent magnetism), unlike iron which is ferromagnetic. The partially filled 4d shell also allows ruthenium to form diverse chemical bonds in complexes.
Isotopes and Nuclear Properties
Naturally occurring ruthenium consists of seven isotopes. The mass numbers 99, 100, 101, 102, and 104 are stable (nonradioactive). The lightest isotope, ^96Ru, is effectively stable with a double–beta decay half-life many times the age of the universe. Another isotope, ^98Ru (1.87% natural abundance), is also stable by common definitions. The most abundant nuclide is ^102Ru (~31.6%), followed by ^104Ru (~18.6%) The others in nature are ^99Ru (12.6%), ^100Ru (12.6%), and ^101Ru (17.1%). All natural isotopes have zero or very long-lived radioactive decay modes.
Several artificial isotopes of ruthenium exist, most produced by nuclear fission or particle accelerators. Notably, ^106Ru (half-life ~374 days) and ^103Ru (half-life ~39 days) are fission products from nuclear reactors and nuclear explosions. These emit β-particles and gamma rays on decay. For example, ^106Ru decays by beta emission to ^106Rh Ruthenium-106 gained public attention when trace amounts were released in a 2017 incident. In nuclear medicine and industry, ^103Ru and ^106Ru can serve as radioactive tracers or brachytherapy sources, but their medical use is limited.
In nuclear chemistry, ruthenium displays nuclear spins in its odd-mass isotopes (e.g. ^99Ru has spin 5/2^+). This makes some isotopes amenable to nuclear magnetic resonance studies, but in practice ^99Ru NMR is rarely used due to its low natural abundance and instrumentation complexities. There are no major applications of Ru isotopes in radiometric dating like uranium–lead or rubidium–strontium systems. However, in geochemistry, traces of Ru in meteorites and ores can provide information about planetary differentiation because Ru is siderophile (iron-loving) and partitioned into metal phases early in Earth’s history.
Allotropes and Typical Compounds
Ruthenium does not have allotropes in the way that carbon or phosphorus do, but it exhibits several crystal forms (polymorphs) under different conditions. The stable form at normal pressure and temperature is hexagonal close-packed (hcp). Under very high temperatures or pressures, it can adopt other structures, but these are of less industrial concern. At room temperature ruthenium metal remains in a hard face-centered arrangement akin to cobalt’s hexagonal form.
Characteristic Bonding: In compounds, ruthenium can form metallic bonds, ionic bonds, and covalent/hydrogen bonds much like other transition metals. It readily forms coordination complexes, often with coordination numbers 4 to 6. For example, ruthenium can bind to ligands like chloride, carbonyl (CO), cyanide (CN⁻), phosphines, and amines. Typical ligands include Cl⁻, NH₃, H₂O, CN⁻, and organic ligands such as C₂H₄ (ethylene) or aromatic rings (in metallocenes like Ru(η^5–C₅H₅)₂, called ruthenocene, an analog of ferrocene). Ruthenium’s multiple valence shells let it engage in π-backbonding with CO or ethylene in organometallic complexes.
Oxides: The key oxides of ruthenium include RuO₂ (ruthenium(IV) oxide), a black solid that is a metallic conductor (widely used as an electrode catalyst), and RuO₄ (ruthenium tetroxide), a yellow volatile compound analogous to osmium tetroxide. RuO₄ is a powerful oxidizing agent (strong enough to oxidize dilute hydrochloric acid and organic solvents even at room temperature and is generally only formed from higher oxides by strong oxidants. Another oxide, KRuO₄ (potassium perruthenate, in which Ru is +7), can be made by oxidizing ruthenates (RuO₄²⁻) and is a strong oxidizer itself. Lower metal-rich oxides like Ru₂O₃ or RuO (Ru in +2 or +3 states) are not well-known, as Ru tends to stabilize +4 or higher. In controlled alkaline fusion, dipotassium ruthenate (K₂RuO₄, Ru +6) forms.
Halides: Chlorides and fluorides are common. Ruthenium trichloride (RuCl₃) is the most important precursor compound; it is a dark solid, often hydrated, and soluble in water (forming reddish solutions) A variety of halides are known, such as RuCl₄ (rare, high oxidation), RuF₆ (orange hexafluoride, Ru+6, made by fluorinating RuF₅), and RuF₅ (green, Ru+5). Metal pattern: RuCl₄ is not stable at standard conditions and often exists only below 0 °C. Lower chlorides exist in mixed forms, and there are oxychlorides (RuOCl₂) from partial hydrolysis. Unlike many metals, ruthenium does not form a simple divalent halide (RuCl₂ must exist as complex salts or oxide-bearing compounds).
Hydrides: Ruthenium does not form stable binary hydrides like some other metals (e.g., there is no RuH₂ known at ambient pressure). In hydrogen atmospheres at high temperature, hydrogen can dissolve into Ru metal or transient Ru–H species in complexes, but no bulk metal hydrides.
Sulfur and Selenium: In sulfides, RuS₂ exists (the mineral laurite, found in platinum ores), and more complex sulfides where Ru is in mixed oxidation states (e.g. Ru₂S₃). These are usually inert, refractory materials and not used industrially. No common soluble sulfide exists.
Other Compounds: Many organoruthenium compounds (containing Ru–C bonds) are important in research and catalysis. For example, Ru₃(CO)₁₂ is a metal carbonyl cluster. The famous Grubbs catalysts for olefin metathesis are based on Ru(II) complexes with phosphine and alkylidene ligands. In solution, aquo complexes [Ru(H₂O)₆]²⁺/³⁺ resemble those of iron and cobalt.
Overall, ruthenium forms compounds in most oxidation states from −2 to +8 (−2 and +8 only in specialized anions or oxide); +2, +3, +4 are the most common oxidation states in typical chemistry Because of this versatility, ruthenium chemistry parallels that of osmium and technetium in many ways.
Physical Properties
Ruthenium is a dense, hard transition metal with a high melting point. Its density is about 12.4 g/cm³ (at room temperature), comparable to osmium and iridium. It has a melting point of about 2607 K (2334 °C) and a boiling point around 4423 K (4150 °C). These high values reflect strong metallic bonding from its partially filled d band. The heat of fusion is around 24 kJ/mol and the heat of vaporization about 595 kJ/mol.
In bulk, ruthenium is a lustrous silvery metal. It is hard and relatively brittle (Mohs hardness around 6). It maintains a shiny appearance in air indefinitely (it “does not tarnish at ambient conditions” Its crystal structure at room temperature is hexagonal close-packed (hcp). Above certain temperatures, other polymorphs can form, but hcp is the only stable form of metallic ruthenium under normal conditions.
As a metal, ruthenium is conductive of heat and electricity, though not as well as copper or silver. Its electrical resistivity at 20 °C is about 7.1×10^−8 Ω·m (0.071 µΩ·cm) giving it a conductivity roughly one-fourth that of copper. Its thermal conductivity is around 117 W/m·K. These values make it a decent conductor, which is why ruthenium oxide films (which remain conductive) are useful as resistor elements. The specific heat capacity is about 0.238 J/(g·K).
Magnetically, ruthenium is paramagnetic at room temperature (no intrinsic magnetic ordering), similar to platinum. The atomic magnetic moment comes from unpaired d electrons, but the overall effect is small. On spectroscopic properties, ruthenium does not have famous atomic emission lines in the visible range used for lighting, nor does it show interesting luminescence as a metal. However, some ruthenium complexes (such as bipyridyl Ru(II) dyes) are intensely colored and luminescent, a property exploited in photovoltaic cells and LEDs.
Ruthenium metal forms a thin passive oxide layer (RuO₂) on its surface, which protects it against further corrosion in many environments. It is attacked by very few reagents at room temperature: for example, it is not dissolved by nitric or sulfuric acid, nor even by aqua regia under mild conditions At elevated temperatures or with strong oxidizers, it will form oxides (RuO₂) or react with halogens and nitrogen oxides to form volatile ruthenium compounds.
Chemical Reactivity and Trends
Ruthenium’s chemical behavior is dominated by its resistance to oxidation and its capability to adopt multiple oxidation states. Pure ruthenium metal is a noble (non-reactive) metal in the chemical sense. It does not react with oxygen or water at ambient conditions. It can withstand acids such as hydrochloric, sulfuric, and even aqua regia (a 3:1 mixture of HCl and HNO₃) without dissolving. This inertness is similar to platinum and much greater than most ferrous metals.
At high temperatures (above about 800 °C), ruthenium will oxidize in air to form RuO₂ on its surface Strong oxidizers can convert ruthenium metal or Ru(IV) oxide into RuO₄ (ruthenium tetroxide), especially in the presence of potent oxidants like sodium metaperiodate or ozone. Halogens (fluorine, chlorine, bromine) will attack solid ruthenium at elevated temperatures, forming halides (e.g. RuF₅/RuF₆, RuCl₃, etc.). For example, fluorine gas reacts with Ru metal around 400 °C to produce a mixture of RuF₃, RuF₅ and RuF₆.
In aqueous chemistry, ruthenium exhibits redox behavior similar to iron. Ruthenium salts can form stable Ru^2+ and Ru^3+ ions (for instance, RuCl₃ in acid yields [RuCl₆]^3− and [RuCl₆]^2− complexes). The standard reduction potential of the Ru^3+ / Ru^2+ couple is +0.455 V (in 1 M HCl), indicating Ru^2+ is a mild reducing agent compared to, say, gold(III). In practice, Ru(III) salts (like RuCl₃) are common precursors; reducing them (e.g. with hydrogen gas) yields Ru(0) metal. The lower oxidation states of +1 or 0 appear in organometallic complexes (metal carbonyls or cyclopentadienyl compounds).
Unlike iron, ruthenium does not form stable low-oxidation oxides or hydroxides. For example, there is no well-known Ru(II) oxide; instead, Ru(II) compounds (such as Ru(OH)2) are quite reducing and tend to convert to Ru(IV) oxide or dissolve. In alkaline solutions, RuO₄ (if ever formed) is reduced to the orange RuO4^− perruthenate. Common bases (like NH₃) form complex cations (e.g. [Ru(NH₃)_6]^3+) rather than deprotonated forms.
One practical chemical trend is surface alloying and passivation. Adding small amounts of Ru to other metals (especially platinum, palladium, or titanium) increases the resistance to corrosion and wear. Ru makes Pt/Pd alloys harder and improves the corrosion behavior of titanium (used in surgical and chemical equipment). Pure ruthenium resists corrosion so well that it is often plated onto cheaper metals to protect them.
In the electrochemical series, ruthenium sits with the noble metals. It is less reactive than iron or copper, about on par with isoelectronic osmium. It will not displace hydrogen from acids, nor is it easily oxidized by weak oxidants. This helps explain its stability as contacts and catalysts. Overall, ruthenium’s reactivity shows it to be a hard, noble metal that only forms compounds under energetic conditions or with strong ligands/oxidizers.
Occurrence and Production
Ruthenium is one of the rarest stable elements in nature. Its crustal abundance is about 100 parts per trillion by weight (only about 0.00001%) It never occurs in large native deposits by itself. Instead, ruthenium is always found alloyed with other platinum-group metals or in trace amounts in certain sulfide and oxide minerals. The most important ruthenium-bearing minerals include laurite (RuS₂, often found in platinum ores) and pentlandite (a nickel–iron sulfide), where small amounts of Ru substitute into the crystal structure. Some platinum ores also contain ruthenite (a rare oxide) or rutheniridosmine (an Ir–Ru alloy).
Major ruthenium reserves lie in the same places as platinum and nickel. The largest known source is the Bushveld Complex in South Africa, a vast layered igneous intrusion rich in platinum-group metals. South African platinum mining yields more than half of the world’s ruthenium (often reported as the largest producer region). Other ruthenium sources include Russia’s Ural Mountains and Norilsk region (from nickel–copper sulfides), small deposits in North America (Sudbury, Ontario), and Zimbabwe. In the late 2010s South Africa contributed roughly seventy to eighty percent of mined ruthenium, with Russia providing most of the rest. (Statista reports indicate North America accounts for only about 1% of supply South African production is often quoted around 20–30 tonnes per year, and total global output is on the order of 30–40 tonnes annually.
Processing: In practice, ruthenium is not mined directly but recovered as a byproduct of other metal refining. It is usually obtained during nickel or copper mining: when sulfide ores are processed, platinum-group elements (PGE) are collected from anode mud in electrolytic refining. In the so-called “nickel residue” or “platinum precipitate,” calcium or arsenic sulfide ore from Ni/Cu smelting, noble metals separate out as solids. Chemical refining steps then isolate each PGM.
A common purification route is to dissolve the PGM mixture in oxidizing acids (such as hot aqua regia) and process precipitates. Ruthenium, osmium, and iridium tend to form insoluble oxides or tetroxides, while platinum, rhodium, and palladium remain in solution. Practically, the residue containing Ru, Os, Ir is treated to separate osmium (by volatilization of OsO₄) from the rest. Ruthenium can be separated from iridium by alkaline fusion or by precipitating as an ammonium hexachlororuthenate ((NH₄)₃RuCl₆), which dissociates to RuO₄ under certain conditions Finally, metallic ruthenium is obtained by reducing Ru salts (such as RuCl₃ or (NH₄)₃RuCl₆) with hydrogen or carbon to yield Ru powder or sponge.
Only a few companies worldwide process ruthenium, mostly in association with platinum refining. Major producers are usually tied to large platinum or nickel mines (e.g. in South Africa, Russia, Zimbabwe, Canada, and a few in Asia). Because ruthenium supply depends on other mining, its availability is relatively fixed and it is considered one of the “minor” PGMs (along with osmium and iridium) due to its smaller output.
Applications and Technology
Ruthenium’s combination of hardness, corrosion resistance, and catalytic versatility makes it valuable in several high-tech applications. Its uses can be grouped largely into electronics, catalysis/chemicals, and niche materials.
Electronics and Electrical Contacts: More than half of ruthenium’s annual consumption goes into the electronics industry. In thick-film chip resistors and hybrid circuits, ruthenium oxide (RuO₂) is used as the resistive material. These ceramic resistors employ coatings or pastes of RuO₂ mixed with glass frit, yielding precise and stable resistances that function up to 100°C and beyond. Similarly, ruthenium or ruthenium–tungsten films are used in capacitor cathodes and resistive films.
Ruthenium metal itself is used in canonical electrical contacts and plating. Even at just 10–30% alloying, ruthenium dramatically improves the wear resistance and conductivity retention of platinum or palladium contacts. For example, Pt–Ru or Pd–Ru alloy contacts in relays and switches resist arcing damage. In fountain pens, tiny amounts of Ru in the Platinum petal alloy make the nib harder. Also, hard disks for computers sometimes use a few nanometers of ruthenium on magnetic layers or underlayers to tune magnetic properties (enhancing data density). A recent development is using ultrathin Ru layers in extreme ultraviolet (EUV) photomasks for semiconductor lithography because of its good reflectivity and stability under radiation.
Catalysis and Chemical Industry: Ruthenium compounds and complexes are important catalysts. In heterogeneous catalysis, Ru metal or RuO₂ catalysts are used for ammonia synthesis or decomposition (though iron is dominant industrially, ruthenium offers high activity in small reactors) and in Fischer–Tropsch processes for converting gases to hydrocarbons on a laboratory scale. In homogeneous catalysis, ruthenium complexes perform many organic transformations. Notably, Grubbs’ metathesis catalysts (based on Ru(II) carbene complexes) are widely used in research and industry for making polymers, pharmaceuticals, and fine chemicals. Other Ru catalysts hydrogenate aldehydes and ketones, couple olefins, or oxidize alcohols.
Ruthenium oxides on titanium (RuO₂/Ti) are used as dimensionally stable anodes (DSA) in chlor-alkali plants and water treatment. These anodes efficiently evolve chlorine or oxygen from brine or water, respectively. They rely on the conductivity and stability of RuO₂ films, which are many times used in chlorate electrolysis and electrolytic cell coatings.
Ruthenium catalysts also play roles in petroleum refining (hydrotreating, desulfurization) and in forming acetic acid (though rhodium-based systems currently lead in industry). In fuel cells, Ru can alloy with platinum to improve catalyst performance for hydrogen oxidation or oxygen reduction in acidic media. Dye-sensitized solar cells often use ruthenium bipyridine complexes (N3 and related dyes) as light-harvesting dyes to convert sunlight to electricity.
Materials and Other Applications: Ruthenium’s hardness and corrosion resistance make it a candidate for hard coatings and alloying in special steels or superalloys (though cost limits this by and large). It is sometimes used in small amounts in platinum jewelry to harden and sometimes give a darker finish. Chemical sensors and memory devices have been proposed using ruthenium’s redox chemistry. In medical research, some ruthenium complexes have been investigated as anticancer agents (analogous to cisplatin) due to their ability to bind DNA, though no ruthenium drug is in widespread use yet.
Overall, the largest single uses are in thick-film resistors and contacts. Industrial machinery, electronics, and transportation rely on small amounts of ruthenium for improved performance and longevity. Its emerging applications (like EUV photomasks and advanced catalysts) reflect ongoing research into this versatile metal.
Biology, Environment, and Safety
Ruthenium has no known biological role in living organisms. It is not an essential nutrient, and very little of it enters the human body under normal conditions. Ruthenium compounds are generally considered only mildly toxic, with toxicity lower than that of some other heavy metals. For example, soluble ruthenium salts (e.g. RuCl₃) can cause skin and eye irritation upon contact, and are harmful if ingested in large quantities. Ruthenium(IV) oxide (RuO₂) is considered hazardous and can irritate respiratory passages as a fine dust; ruthenium tetroxide (RuO₄) is extremely toxic by inhalation or contact, akin to osmium tetroxide, but it is not encountered except in specialized lab operations.
Because ruthenium is so scarce, environmental chemistry is not well studied. It likely has no significant natural biogeochemical cycle. Anthropogenic ruthenium mainly comes from industrial waste or wear debris of electronics and catalysts. Any released metal or soluble salts would be expected to behave like other heavy metals: binding strongly to soils and sediments. The highest public interest in environmental ruthenium has been due to nuclear incidents: for example, traces of ^106Ru in the atmosphere were detected after nuclear accidents, raising concern as a long-lived fission product.
In terms of safety regulations, there are no specific exposure limits for ruthenium beyond those for metals or inorganic compounds in general. Standard precautions for handling powders and solutions apply: use gloves, goggles, and avoid inhaling dust or mist. In laboratory settings, ruthenium(III) and ruthenium(IV) compounds should be handled under a fume hood. Metallic ruthenium, being inert, is of low toxicity if ingested (it passes through the body largely unchanged), but giant doses should still be avoided. As with all heavy metals, chronic ingestion or high exposure could pose health risks (kidney or liver effects).
For most practical purposes, ruthenium is considered safer to use than many more toxic metals. However, ruthenium hexafluoride, tetroxide, and some complex compounds can present chemical hazards. Disposal of ruthenium-contaminated waste generally follows heavy-metal waste guidelines. In summary, ruthenium’s environmental and biological footprints are minor, but it should be treated with care in industry and laboratory use, like any heavy metal.
History and Etymology
Ruthenium was the last of the platinum-group metals to be discovered. Its story begins in the early 19th century when chemists investigating platinum ores found unexpected residues. In 1808, Polish chemist Józef Sniadecki thought he had discovered a new metal in platinum-bearing materials from Brazil, calling it “vestium,” but he later withdrew his claim. He was followed in 1828 by the German chemist Gottfried Osann, who, working with platinum ore from Russia’s Ural Mountains, reported three new elements: “pluranium,” “polinium,” and “ruthenium.” It turned out only ruthenium was real; the others were spurious. The name “ruthenium” comes from Ruthenia, the Latin word for Russia, honoring the ore’s geographic source
The credit for isolating pure Ruthenium goes to Russian chemist Karl Ernst Claus in 1844 (sometimes given as Karl Karlovich Klaus). He independently analyzed the Ural platinum ores, identified an unrecognized metal, and provided a clear description of ruthenium metal. He chose to retain Osann’s name “ruthenium” for the new element. Claus showed that Ruthenium had distinct chemistry and obtained it as a violet chloride before reducing it to metallic ruthenium.
Since its discovery, ruthenium has seen slow but steady integration into technology. Initially, its rarity limited use, and it was mostly a laboratory curiosity. In the early 20th century, the refinement of nickel and platinum ores (especially electrorefining) made ruthenium available in larger quantities. In 1927 the first electrochemical uses of RuO₂ were patented for chlorine production. In the 1940s–50s, platinum–ruthenium alloys began to appear in industry (for spark plugs, laboratory crucibles, and some chemical reactors) to exploit Ru’s hardness and toughness. The semiconductor era brought ruthenium as a thin-film material for resistors and contacts.
The historical significance of ruthenium is tied to its role as a connector between discovery and modern applications: it was discovered at a time of active element hunting, and later found niche uses in catalysts and electronics. Its name is a reminder of scientific cooperation across borders (Polish and Russian chemists in its story) as well as a legacy of 19th-century mineralogy (“Ruthenian metal”). Today, ruthenium remains a notable example of how even very rare elements can become technologically important.
Data Table
| Property | Value |
|---|---|
| Symbol | Ru |
| Atomic number (Z) | 44 |
| Category | Transition metal (platinum group) |
| Standard atomic weight | 101.07 |
| Electron configuration | [Kr] 4d^7 5s^1 |
| Common oxidation states | –2, 0, +2, +3, +4, +6, +8 |
| Standard state (20 °C) | Solid (metal) |
| Crystal structure | Hexagonal close-packed (hcp) at RT |
| Density | ~12.4 g/cm³ (at 20 °C) |
| Melting point | 2334 °C (2607 K) |
| Boiling point | 4150 °C (4423 K) |
| Heat of fusion | 24 kJ/mol |
| Heat of vaporization | 595 kJ/mol |
| Thermal conductivity | 117 W/(m·K) |
| Electrical resistivity | 7.1×10^−8 Ω·m (at 20 °C) |
| First ionization energy | 710 kJ/mol |
| Electronegativity (Pauling) | 2.2 |
| Atomic radius (covalent) | ~1.34 Å |
| Isotopes (naturally occ.) | ^99Ru, ^100Ru, ^101Ru, ^102Ru, ^104Ru (and minor ^96Ru, ^98Ru) |
| Stable isotopic composition | ^102Ru (31.6%), ^104Ru (18.6%), ^101Ru (17.1%), ^99Ru (12.6%), ^100Ru (12.6%), ^96Ru (5.5%), ^98Ru (1.9%) |
| Notable isotope (radio) | ^106Ru (β^–, t₁/₂ ≈374 d), as nuclear fission product |
| Common minerals | Laurite (RuS₂), Heazlewoodite (Ni₃S₂, contains Ru) |
| Major ore sources | Bushveld Complex (S. Africa), Norilsk (Russia), Sudbury (Canada) |
| CAS Registry Number | 7440-18-8 |