Like other groups, the members of this family show patterns inelectron configuration, especially in the outermost shells, resulting in trends in chemical behavior; however, rhodium deviates from the pattern.
Cobalt compounds have been used for centuries to impart a rich blue color toglass,glazes, andceramics. Cobalt has been detected in Egyptian sculpture, Persian jewelry from the third millennium BC, in the ruins ofPompeii, destroyed in 79 AD, and in China, dating from theTang dynasty (618–907 AD) and theMing dynasty (1368–1644 AD).[5]
Rhodium was discovered in 1803 byWilliam Hyde Wollaston,[8] soon after he discoveredpalladium.[9][10][11] He used crudeplatinum ore presumably obtained fromSouth America.[12] His procedure dissolved the ore inaqua regia and neutralized the acid withsodium hydroxide (NaOH). He then precipitated the platinum asammonium chloroplatinate by addingammonium chloride (NH 4Cl). Most other metals likecopper,lead,palladium, and rhodium were precipitated withzinc. Dilutednitric acid dissolved all but palladium and rhodium. Of these, palladium dissolved inaqua regia but rhodium did not,[13] and the rhodium was precipitated by the addition ofsodium chloride asNa 3[RhCl 6]·nH 2O. After being washed with ethanol, the rose-red precipitate was reacted with zinc, whichdisplaced the rhodium in the ionic compound and thereby released the rhodium as free metal.[14]
Chemists who studied platinum dissolved it inaqua regia (a mixture ofhydrochloric andnitric acids) to create soluble salts. They always observed a small amount of a dark, insoluble residue.[15] In 1803, British scientistSmithson Tennant (1761–1815) analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternately with alkali and acids[16] and obtained a volatile new oxide, which he believed to be of this new metal—which he namedptene, from the Greek wordπτηνόςptēnós, "winged".[17][14] Tennant, who had the advantage of a much greater amount of residue, continued his research and identified the two previously undiscovered elements in the black residue, iridium and osmium.[15][16] He obtained dark red crystals (probably ofNa 2[IrCl 6]·nH 2O) by a sequence of reactions withsodium hydroxide andhydrochloric acid.[14] He named iridium afterIris (Ἶρις), the Greek winged goddess of the rainbow and the messenger of the Olympian gods, because many of thesalts he obtained were strongly colored.[a][18] Discovery of the new elements was documented in a letter to theRoyal Society on June 21, 1804.[15][19]
The first three elements are hard silvery-white metals:
Cobalt is a metallic element that can be used to turn glass a deep blue color. Cobalt is primarily used inlithium-ion batteries, and in the manufacture ofmagnetic, wear-resistant and high-strengthalloys. The compounds cobalt silicate andcobalt(II) aluminate (CoAl2O4, cobalt blue) give a distinctive deep blue color toglass,ceramics,inks,paints andvarnishes. Cobalt occurs naturally as only one stableisotope, cobalt-59.Cobalt-60 is a commercially important radioisotope, used as aradioactive tracer and for the production of high-energygamma rays. Cobalt is also used in the petroleum industry as a catalyst when refining crude oil. This is to clean it of its sulfur content, which is very polluting when burned and causes acid rain.
Rhodium can be used in jewelry as a shiny metal. Rhodium is a hard, silvery, durable metal that has a highreflectance. Rhodium metal does not normally form anoxide, even when heated.Oxygen is absorbed from theatmosphere only at themelting point of rhodium but is released on solidification. Rhodium has both a higher melting point and lowerdensity thanplatinum. It is not attacked by mostacids as it is completely insoluble innitric acid and dissolves slightly inaqua regia.
Iridium is mainly used as a hardening agent for platinum alloys. Iridium is the mostcorrosion-resistant metal known as it is not attacked byacids, includingaqua regia. In the presence of oxygen, it reacts withcyanide salts. Traditional oxidants also react, including thehalogens and oxygen at higher temperatures. Iridium also reacts directly withsulfur at atmospheric pressure to yieldiridium disulfide.
All knownisotopes of meitnerium are radioactive with short half-lives. Only minute quantities have been synthesized in laboratories. It has not been isolated in pure form, and its physical and chemical properties have not been determined yet.[citation needed] Based on what is known, meitnerium is considered a homologue to iridium.
Of the group 9 elements, only cobalt has a biological role. It is a key constituent ofcobalamin, also known as vitamin B12, the primary biological reservoir of cobalt as anultratrace element.[22][23]Bacteria in the stomachs ofruminant animals convert cobalt salts into vitamin B12, a compound which can only be produced by bacteria orarchaea. A minimal presence of cobalt in soils therefore markedly improves the health ofgrazing animals, and an uptake of 0.20 mg/kg a day is recommended, because they have no other source of vitamin B12.[24]
Proteins based on cobalamin usecorrin to hold the cobalt. Coenzyme B12 features a reactive C-Co bond that participates in the reactions.[25] In humans, B12 has two types ofalkylligand:methyl and adenosyl.MeB12 promotes methyl (−CH3) group transfers. The adenosyl version of B12 catalyzes rearrangements in which a hydrogen atom is directly transferred between two adjacent atoms with concomitant exchange of the second substituent, X, which may be a carbon atom with substituents, an oxygen atom of an alcohol, or an amine.Methylmalonyl coenzyme A mutase (MUT) convertsMMl-CoA toSu-CoA, an important step in the extraction of energy from proteins and fats.[26]
^Georg Brandt first showed cobalt to be a new metal in: G. Brandt (1735) "Dissertatio de semimetallis" (Dissertation on semi-metals),Acta Literaria et Scientiarum Sveciae (Journal of Swedish literature and sciences), vol. 4, pages 1–10. See also:(1) G. Brandt (1746) "Rön och anmärkningar angäende en synnerlig färg—cobolt" (Observations and remarks concerning an extraordinary pigment—cobalt),Kongliga Svenska vetenskapsakademiens handlingar (Transactions of the Royal Swedish Academy of Science), vol. 7, pp. 119–130;(2) G. Brandt (1748) "Cobalti nova species examinata et descripta" (Cobalt, a new element examined and described),Acta Regiae Societatis Scientiarum Upsaliensis (Journal of the Royal Scientific Society of Uppsala), 1st series, vol. 3, pp. 33–41;(3) James L. Marshall and Virginia R. Marshall (Spring 2003)"Rediscovery of the Elements: Riddarhyttan, Sweden".The Hexagon (official journal of theAlpha Chi Sigma fraternity of chemists), vol. 94, no. 1, pages 3–8.
^Usselman, Melvyn (1978). "The Wollaston/Chenevix controversy over the elemental nature of palladium: A curious episode in the history of chemistry".Annals of Science.35 (6):551–579.doi:10.1080/00033797800200431.
^Münzenberg, G.; Armbruster, P.; Heßberger, F. P.; Hofmann, S.; Poppensieker, K.; Reisdorf, W.; Schneider, J. H. R.; Schneider, W. F. W.; Schmidt, K.-H.; Sahm, C.-C.; Vermeulen, D. (1982). "Observation of one correlated α-decay in the reaction58Fe on209Bi→267109".Zeitschrift für Physik A.309 (1): 89.Bibcode:1982ZPhyA.309...89M.doi:10.1007/BF01420157.S2CID120062541.
^Yamada, Kazuhiro (2013). "Chapter 9. Cobalt: Its Role in Health and Disease". In Astrid Sigel; Helmut Sigel; Roland K. O. Sigel (eds.).Interrelations between Essential Metal Ions and Human Diseases. Metal Ions in Life Sciences. Vol. 13. Springer. pp. 295–320.doi:10.1007/978-94-007-7500-8_9.ISBN978-94-007-7499-5.PMID24470095.
^Schwarz, F. J.; Kirchgessner, M.; Stangl, G. I. (2000). "Cobalt requirement of beef cattle – feed intake and growth at different levels of cobalt supply".Journal of Animal Physiology and Animal Nutrition.83 (3):121–131.doi:10.1046/j.1439-0396.2000.00258.x.
^Smith, David M.; Golding, Bernard T.; Radom, Leo (1999). "Understanding the Mechanism of B12-Dependent Methylmalonyl-CoA Mutase: Partial Proton Transfer in Action".Journal of the American Chemical Society.121 (40):9388–9399.doi:10.1021/ja991649a.
