Ruthenium (Ru)

• Element Symbol: Ru
• Atomic Number: 44
• Atomic Mass: 101.07
• Group # in Periodic Table: 8
• Group Name: Transition metals
• Period in Periodic Table: 5
• Block of Periodic Table: d-block
• Discovered by: Karl Ernst Claus (1844)

Ruthenium is a chemical element of the periodic table. It is considered a platinum-group metal, a classification that also includes rhodium, palladium, osmium, iridium, and platinum. These platinum-group metals are all transition metals, which typically form colored compounds and have strong valence (the ability of an atom to connect chemically to another atom).

In 1825 scientists Gottfried Osann and Jöns Jacob Berzelius began experimenting with platinum that had been found in the Ural Mountains of Russia. Upon dissolving in aqua regia, the platinum left a residue in which Osann believed he could identify three new metals, which he called "polinium," "pluranium," and "ruthenium." However, Berzelius did not believe this to be a valid finding, and because Osann could not repeat the circumstances that led to the isolation of ruthenium, he withdrew his claim of its discovery. Almost two decades later, in 1844, Karl Ernst Claus also identified ruthenium in the residue left over from platinum. Claus kept the name "ruthenium," derived from the Latin word for Russia, in honor of Osann’s contributions.

Physical Properties

Ruthenium is a silvery-gray metal that is visually similar to platinum. At 298 kelvins (K), ruthenium’s standard state is a hard, brittle solid with low ductility; it is rated as a 6.5 on the Mohs hardness scale. In this solid state, it has a density of 12.37 grams per cubic centimeter (g/cm³). Ruthenium does not easily tarnish when exposed to air, but in temperatures above 800 degrees Celsius (°C), it begins to oxidize. The melting point of ruthenium is 2334 °C, and its boiling point is 4150 °C. These values are quite high, which is a common characteristic of transition metals. In addition, due to ruthenium’s high melting point, the metal is not easily cast or reshaped.

The specific heat of ruthenium is 238 joules per kilogram-kelvin (J/kg·K). Ruthenium is a good conductor, with an electrical conductivity of 1.4 × 10⁷ siemens per meter (S/m). Its thermal conductivity is 120 watts per meter-kelvin (W/m·K). Ruthenium is paramagnetic, which means that it is magnetized when placed within a magnetic field, but it does not retain this property upon removal.

Chemical Properties

The most common oxidation states of ruthenium are +2, +3, and +4. Ruthenium has a hexagonal close-packed crystal structure and it is generally inert with most chemicals, with the exception of potassium chlorate, the addition of which can result in an explosion. Naturally occurring ruthenium consists of seven stable isotopes, the most abundant of which, ruthenium-102, makes up 31.6 percent of naturally occurring ruthenium. The element also has thirty-four known radioactive isotopes. Ruthenium-106, ruthenium-103, and ruthenium-97 are the most stable of these isotopes, with half-lives of 373.59 days, 39.26 days, and 2.9 days, respectively. Unstable ruthenium isotopes with mass numbers less than 102 undergo electron capture, a form of radioactive decay in which one of the atom’s electrons is absorbed by the nucleus, transforming a proton into a neutron and a neutrino. In ruthenium, this process usually results in technetium isotopes. Unstable ruthenium isotopes with mass numbers greater than 102 undergo beta decay, another form of radioactive decay, in which a proton is converted into a neutron (or vice versa) inside the nucleus of an atom. When a ruthenium atom goes through this process, energy is released in the form of a beta particle (a fast-moving electron or positron), usually resulting in isotopes of rhodium.

Applications

Ruthenium occurs extremely rarely in Earth’s crust, existing at only about 0.001 parts per million, making it the seventy-fourth most abundant element. The element can be found alongside fellow platinum-group metals in natural mineral sources that are usually located in the Ural Mountains of Russia. It can also be found in pyroxenite rock in South Africa and in pentlandite found in North and South America. It is from these sources that ruthenium is commercially mined, with about twelve metric tons mined annually and five thousand metric tons in reserves. Additionally, ruthenium is formed as a product of nuclear fission when uranium and plutonium are placed in nuclear reactors. Ruthenium has no biological role, but compounds of ruthenium in particular are treated as highly toxic, and any ingested is most commonly stored in the bones. This retained ruthenium can be dangerous, acting as a carcinogen, which increases the risk of cancer development in those exposed. Those ruthenium compounds that come in contact with the skin leave a resilient stain.

Ruthenium is continuing to find more and more uses in various industries. It is commonly alloyed with platinum and palladium to create durable electrical switches. Additionally, ruthenium compounds are used in the production of chip resistors, which maintain safe electrical currents in electronics. Just 0.1 percent ruthenium added to titanium can increase its resistance to corrosion by 1,000 percent. Similarly, ruthenium can be added to other materials to create high-performance alloys, some of which are used in the blades of jet engines. Ruthenium compounds are also good chemical catalysts and find uses in the production of chlorine from saltwater and ammonia from natural gas. Certain ruthenium compounds have also been found to absorb visible light and are beginning to find uses in technologies for solar energy.

Bibliography

Crabtree, Robert H. The Organometallic Chemistry of the Transition Metals. 6th ed. Hoboken: Wiley, 2014. Print.

Emsley, John. Nature’s Building Blocks: An A–Z Guide to the Elements. 2nd ed. New York: Oxford UP, 2011. Print.

Halka, Monica, and Brian Nordstrom. Transition Metals. New York: Facts on File, 2011. Print.

Haynes, William M., ed. CRC Handbook of Chemistry and Physics. 95th ed. Boca Raton: CRC, 2014. Print.

"Technical Data for Ruthenium." The Photographic Periodic Table of the Elements. Element Collection, n.d. Web. 18 Aug. 2015.