134 | The History and Use of Our Earth’s Chemical Elements than iron. Although there are some similar characteristics between ruthenium and iron,
134 | The History and Use of Our Earth’s Chemical Elements than iron. Although there are some similar characteristics between ruthenium and iron,
ruthenium’s properties are more like those of osmium. Even so, ruthenium is less stable than osmium. They are both rare and difficult to separate from minerals and ores that con- tain other elements. These factors make it more difficult to determine ruthenium’s accurate atomic weight.
The oxidation state of +8 for ruthenium and its “mate” osmium is the highest oxidation state of all elements in the transition series. Ruthenium’s melting point is 2,310°C, its boiling
point is 3,900°C, and its density is 12.45 g/cm 3 .
Characteristics Ruthenium also belongs to the platinum group, which includes six elements with similar
chemical characteristics. They are located in the middle of the second and third series of the transition elements (groups 8, 9, and 10). The platinum group consists of ruthenium, rho- dium, palladium, osmium, iridium, and platinum.
Ruthenium is a hard brittle metal that resists corrosion from all acids but is vulnerable to strong alkalis (bases). Small amounts, when alloyed with other metals, will prevent corrosion of that metal.
AbundanceandSource Ruthenium is a rare element that makes up about 0.01 ppm in the Earth’s crust. Even so, it
is considered the 74th most abundant element found on Earth. It is usually found in amounts up to 2% in platinum ores and is recovered when the ore is refined. It is difficult to separate from the leftover residue of refined platinum ore.
Ruthenium is found in South America and the Ural Mountains of Russia. There are some minor platinum and ruthenium ores found in the western United States and Canada. All of the radioactive isotopes of ruthenium are produced in nuclear reactors.
History There is a long and mixed history for the claims of discovery for ruthenium. In 1748
Antonio de Ulloa (1716–1795), a Spanish scientist and explorer, reported finding a special metal in South America. It was silvery-gray and denser than gold, but it did not have the attractive luster of gold or silver. He did know that he had located a new element along with the platinum metal.
In 1807 Jedrzej Sniadecki (1768–1807), a Polish scientist, was the first to isolate the new element and assign it the atomic number 44. He named his new element “Vesta” after
a large asteroid and wrote several papers describing his discovery. The Paris Commission, the scientific society of the day, ignored Sniadecki’s work because he was not famous and the commission could not replicate his work. Rather than argue with the commission, Sniadecki dropped his claim. Regardless, some sources give Sniadecki credit for the discov- ery of ruthenium.
In 1827 or 1828 Gottfried Wilhelm Osann (1796–1866), a well-known German scientist, found in the Ural mountains of Russia what he claimed were several new elements in plati- num ores, including ruthenium. However, after his announcement, nothing more happened and he did not withdraw his claim, as did Sniadecki. Some sources now give Osann credit for discovering ruthenium.
135 It was not until 1844 that Karl Karlovich Klaus (1796–1864), a well-known Russian
Guide to the Elements |
(Estonian) scientist of the day, separated enough ruthenium from platinum to be able to correctly identify its properties. He is the person most sources credit as the “discoverer” of
44 Ru. If Sniadecki had not withdrawn his claim, he may have, eventually, been credited with the discovery of ruthenium. However, as history stands, Osann is credited with first finding ruthenium and Klaus for adequately identifying its properties to determine that it fit into the “hole” in the periodic table for element 44.
CommonUses Since ruthenium is rare and difficult to isolate in pure form, there are few uses for it. Its
main uses are as an alloy to produce noncorrosive steel and as an additive to jewelry metals such as platinum, palladium, and gold, making them more durable.
It is also used as an alloy to make electrical contacts harder and wear longer, for medical instruments, and more recently, as an experimental metal for direct conversion of solar cell material to electrical energy.
Ruthenium is used as a catalyst to affect the speed of chemical reactions, but is not altered by the chemical process. It is also used as a drug to treat eye diseases.
ExamplesofCompounds The most common oxidation state for ruthenium is +3 as the metal ion Ru 3+ :
Ruthenium(III) trichloride: Ru 3+ + 3Cl → RuCl 3 .
This compound is used for technical analysis in chemistry laboratories. It is highly toxic.
Ruthenium(III) hydroxide: Ru 3+ + 3(HO) 1- → Ru(OH) 3 .
Examples of oxides of ruthenium with higher oxidation states follow:
Ruthenium(IV) oxide: Ru 4+ +2O 2- → RuO 2 . Ruthenium(VIII) oxide: Ru 8+ + 4O 2- → RuO 4 .
Hazards The main hazard is the explosiveness of ruthenium fine power or dust. The metal will
rapidly oxidize (explode) when exposed to oxidizer-type chemicals such as potassium chlo- ride at room temperature. Most of its few compounds are toxic and their fumes should be avoided.
RHODIUM SYMBOL:Rh PERIOD:5 GROUP:9(VIII) ATOMICNO:45
ATOMICMASS:102.906amu VALENCE:3 OXIDATIONSTATE:+3(also+4in compounds) NATURALSTATE:Solid ORIGINOFNAME:NamedaftertheGreekwordrhodon,whichmeans“rose,”becauseof thereddishcolorofitssaltcompounds. ISOTOPES:Thereare52isotopesofrhodium,rangingfromRh-89toRh-122.Allarepro- ducedartificiallywithrelativelyshorthalf-livesexceptonestableisotope,Rh-103,which constitutes100%oftheelement’sexistenceintheEarth’scrust.
136 | The History and Use of Our Earth’s Chemical Elements
ELECTRONCONFIGURATION EnergyLevels/Shells/Electrons Orbitals/Electrons
s2,p6
3-M=18
s2,p6,d10
4-N=16
s2,p6,d8
5-O=1
s1
Properties Rhodium is a hard shiny-white metal that resists corrosion from oxygen, moisture, and
acids at room temperatures. As a member of group 8 (VIII), 45 Rh shares many chemical and physical properties with cobalt ( 27 Co) just above it and iridium ( 77 Ir) below it in the vertical group. Therefore, it is considered one of the elements that are transitory between metals and nonmetals. It is rare and only found in combination with platinum ores.
Rhodium’s melting point is 1,966°C, its boiling point is 3,727°C, and its density is 12.41 g/cm 3 .
Characteristics Rhodium is one of the six platinum transition elements that include Ru, Rh, Pd, Os, Ir, and
Pt. Of these metals, rhodium has the highest electrical and thermal conductivity. Although a relatively scarce metal, rhodium makes an excellent electroplated surface that is hard, wears well, and is permanently bright—ideal for plating the reflectors in automobile headlights.
AbundanceandSource Rhodium is rare, but not as rare as ruthenium. It makes up only 1 part in 20 million of the
elements found in the Earth’s crust. Even so, it is considered the 79th most abundant element and is found mixed with platinum ore, and to a lesser extent, it is found with copper and nickel ores. It is found in Siberia, South Africa, and Ontario, Canada.
Rhodium is recovered from platinum and other ores by refining and purification processes that start by dissolving the other platinum group metals and related impurities with strong acids that do not affect the rhodium itself. Any remaining platinum group elements are removed by oxidation and bathing the mixture in chlorine and ammonia.
Rhodium is usually produced as a powder and can be formed by either casting or powder metallurgy.
History William Hyde Wollaston (1766–1828), who had also discovered palladium ( 46 Pd) in
the early 1800s, announced in 1803 his discovery of another metal that he had isolated
137 from platinum ores found in South America. His procedures were rather complicated but
Guide to the Elements |
resulted in the discovery of several platinum-related metals. He used these newly discovered metals, rhodium and iridium, to alloy with platinum to make improved laboratory vessels that were harder and more durable than pure platinum as well as noncorrosive. Wollaston derived great wealth from this refining process, the details of which were not disclosed until his death in 1828.
CommonUses Rhodium is commercially used as an alloy metal with other metals to form durable high-
temperature electrical equipment, thermocouples, electrical contacts and switches, and labo- ratory crucibles.
Because of its high reflectivity, it is used to electroplate jewelry, silverware, optical instru- ments, mirrors, and reflectors in lighting devices. When rhodium is combined with platinum and palladium, the elements together form the internal metals of automobile catalytic converters, which convert hot unburned hydrocarbon exhaust gases to less harmful CO 2 and H 2 O. Similar alloys are used to manufacture high- temperature products such as electric coils for metal refining furnaces and high-temperature spark plugs.
ExamplesofCompounds The most common oxidation state of rhodium is +3, but it can also exhibit ions of +2 and
+4 in certain compounds. Rhodium(III) trichloride: Rh 3+ + 3Cl 1- → RhCl 3.
Rhodium(III) oxide: Rh 3+ + 3O 2- → Rh 2 O 3.
Rhodium(IV) oxide: Rh 4+ + 2O 2- → RhO 2. Several other complicated compounds exist as well: Sodium rhodium chloride (Na 3 RhCl 6 • 12H 2 O) is the hydrate form of rhodium that was first produced by Wollaston. A similar compound is formed as potassium rhodium sulfate (K 3 Rh(SO 4 ) 3 , which is a rose-colored crystal. Of some interest are the different colored crystals resulting from compounding rhodium with the halogens: RhF 3 = red, RhCl 3 = red, RhBr 3 = brown, and ReI 3 = black.
Hazards The powder and dust of rhodium metal are flammable in air. Some of the compounds may
cause skin irritations. It is best to use approved laboratory procedures when handling any of the six elements in the platinum family of metals.
PALLADIUM SYYMBOL:Pd PERIOD:5 GROUP:10(VIII) ATOMICNO:46
ATOMICMASS:106.42amu VALENCE:2,3,and4 OXIDATIONSTATE:+2,+3,and +4 NATURALSTATE:Solid ORIGINOFNAME:PalladiumisnamedaftertheasteroidPallas,whichwasdiscoveredat aboutthesametimeastheelement.PallasisthenameoftwomythologicalGreekfig- ures,onemaleandtheotherfemale.