Platinum Metals Rev., 2008, 52, (2), 114–119 114

The Periodic Table and the PlatinumGroup MetalsBy W. P. GriffithDepartment of Chemistry, Imperial College, London SW7 2AZ, U.K.; E-mail: w.griffith@imperial.ac.uk

The year 2007 marked the centenary of the death of Dmitri Mendeleev (1834–1907). Thisarticle discusses how he and some of his predecessors accommodated the platinum groupmetals (pgms) in the Periodic Table, and it considers the placing of their three transuraniccongeners: hassium (108Hs), meitnerium (109Mt) and darmstadtium (110Ds). Over twenty-fiveyears ago McDonald and Hunt (1) wrote an excellent account of the pgms in their periodiccontext. This account is indebted to that work. The present article introduces new perspectivesand shows some of the relevant tables. There are good books on the history of the PeriodicTable, e.g. (2, 3) and other texts (4, 5) which provide a fuller picture than it is possible togive here.

DOI: 10.1595/147106708X297486

Discovery and Early Classificationof the Platinum Group Metals

Antoine-Laurent Lavoisier (1743–1794) in 1789defined the element as being “the last point thatanalysis can reach”, and it was largely this clear state-ment which brought about the discovery of 51 newelements in the nineteenth century alone. JohnDalton’s (1766–1844) recognition in 1803 of theatom as being the ultimate constituent of an element,with its own unique weight, was crucial. StanislaoCannizzaro (1826–1910), at the celebrated KarlsruheCongress (1860), published a paper recognising thetrue significance of Avogadro’s molecular hypothesisand thereby clarified the difference between atomicand molecular weights. From then, reasonably accu-rate atomic weights of known elements becamereadily available and greatly helped the constructionof useful Periodic Tables. Atomic (or elemental)weights were useful but were not a sine qua non fortable construction. A number of tables were pro-duced with incorrect values, or, as Mendeleev laternoted, inconsistencies in published atomic weightsbecame apparent from these tables. We have thebenefit of hindsight and know that atomic numbersare crucial factors for periodicity.

Platinum is a metal of antiquity, but the other fivepgms were isolated in the nineteenth century. Thebicentenaries of four were marked in this Journal:William Hyde Wollaston’s (1766–1828) discovery of

palladium and rhodium in 1802 and 1804 (6) andSmithson Tennant’s (1761–1815) isolation of iridi-um and osmium in 1804 (7, 8). Ruthenium was thelast to be isolated, by Karl Karlovich Klaus(1796–1864) in 1844 (9–11). Thus, five of the sixwere known by 1804, and the sixth by 1844, in goodtime for the development of the Periodic Table.

The pgms are now known to fall into two hori-zontal groups: Ru-Rh-Pd and Os-Ir-Pt, but webenefit from some 200 years of hindsight in thisobservation. Johann Döbereiner (1780–1849) notedsimilarities in the chemical behaviour of ‘triads’ ofelements, in which the equivalent weight of the mid-dle element lay roughly halfway between those of theother two. In 1829, when Professor of Chemistry atJena, he used his equivalent weights for these metals(based on oxygen = 100) to demonstrate that Pt-Ir-Os and Pd-‘pluran’-Rh ‘triads’ existed (12). ‘Pluran’had been reported together with two other ‘new’ ele-ments in 1827 by Gottfried Osann (1796–1866). Itmay possibly have contained some ruthenium, butBerzelius was unable to confirm the novelty of thesethree elements, and Osannn subsequently withdrewhis claim (13).

In 1853 John Hall Gladstone (1827–1902), thena chemist at St. Thomas’s Hospital, London, notedthat the Rh-Ru-Pd triad was related to that ofPt-Ir-Os, while the ‘atomic weights’ (sic) of the lattertriad were roughly twice those of the former (14). In

Platinum Metals Rev., 2008, 52, (2) 115

1857 William Odling (1829–1921), then teachingchemistry at Guy’s Hospital, London, noted thegreat similarity of Pd, Pt and Ru, that the ‘atomicweight’ (sic) of Pt (98.6) was about twice that of Pd(53.2), and that Pt, Ir and Os were chemically similar(15). The stage was now set for a periodic classifica-tion of these and indeed all the elements thenknown.

The Development of PeriodicClassifications

In 1862 Alexandre-Emile Béguyer deChancourtois (1820–1886), Professor at the Écoledes Mines, Paris, devised a ‘vis tellurique’ (telluricscrew) (16), a helix on a vertical cylinder on whichsymbols of the elements were placed at heights pro-portional to their atomic weights. Although somepgms appeared on it (Rh and Pd on one incline andIr and Pt on another), no relationships betweenthem are discernible.

Karl Karlovich Klaus, then professor of chem-istry at the University of Kazan (now in Tatarstan),had discovered Ru in 1844 (9–11) and knew moreabout the pgms than anyone else. In 1860he arranged the three most abundant ones in aPrincipal series (Haupt Reihe), and beneath themplaced a Secondary series (Neben Reihe), notingalso the chemical similarities of each vertical pair(17–19) (Figure 1 (18)).

Klaus’s table shows the correct vertical pairs, butnot in the now accepted sequence. The pgms werenot set in the context of other elements. In 1864 theanalytical chemist John Alexander Raina Newlands(1837–1898) proposed the first of his tables, arrang-ing the known 61 elements in order of ascendingatomic weights (20, 21). In his subsequent ‘law ofoctaves’ he noted that the chemical properties ofsome elements were repeated after each series ofseven, and assigned ordinal numbers to elements inthe sequence of their ascending atomic weights: an

early form of the atomic number (e.g. H = 1, Li = 2etc.) (22). Although the pgms featured in Newlands’stables they were often out of place. William Odling(born, like Newlands, in Southwark, London),whose pgm triads we have noted above (15), pro-duced in 1864 a table of 61 elements in which the sixpgms were grouped together (Ro is rhodium). Hewas the first to arrange them in a reasonably logicalway in a Periodic Table (Figure 2) (23).

The stage was now set for two giants of periodic-ity, Lothar Meyer and, above all, Dmitri Mendeleev.In 1868 Julius Lothar Meyer (1830–1895), Professorof Chemistry at Tübingen arranged 52 elements inan unpublished table with Ru & Pt, Rh & Ir, Pd &Os side-by-side. His slightly later table, published in1870 (24), places the pgms correctly, but a numberof other elements lie in a sequence different fromthat of modern tables:

Mn = 54.8 Ru = 103.5 Os = 198.6?Fe = 55.9 Rh = 104.1 Ir = 196.7Co = Ni = 58.6 Pd = 106.2 Pt = 196.7

On 6th March, 1869, Dmitri Mendeleev(1834–1907) produced his first table (25, 26).Mendeleev was born in Tobolsk, Siberia, the last offourteen children. His father became blind whenDmitri was sixteen, and his indomitable mother,determined that he should be well educated, hitch-hiked with him on the 1400 mile journey to theUniversity at Moscow. Here he was refused admit-tance because he was Siberian; they travelled afurther 400 miles to St. Petersburg. There in 1850Mendeleev got a job as a trainee teacher; his motherdied from exhaustion in the same year. In 1866, aftera spell of study in Germany (he had attended the1860 Karlsruhe Congress) and France, Mendeleevbecame Professor of Chemistry at the University ofSt. Petersburg.

Mendeleev’s interest in periodicity may well havedated from the Karlsruhe Congress and been

Fig. 1 Klaus’s arrangement of theplatinum group metals of 1864 (18)

Platinum Metals Rev., 2008, 52, (2) 116

cemented by a textbook on inorganic chemistry, partof which he finished in 1868. More than any of hispredecessors in the field of periodicity, he had aremarkable knowledge of the chemistry of the ele-ments. His first published version placed the pgmstogether but with unusual pairings (25, 26):

Rh 104.4 Pt 197.4Ru 104.4 Ir 198Pd 106.6 Os 199

The version normally regarded as Mendeleev’sdefinitive table appeared in 1871, first printed in aRussian journal (27) and then reprinted in Annalen inthe same year (Figure 3) (28). By then Mendeleevhad seen Lothar Meyer’s paper and almost certainlyknew of Newlands’s and Odling’s work, but his tablerepresents a major advance in classification of theelements, for the first time placing the pgms in theirmodern sequence and in context. The dashes underthe Ru-Rh-Pd-Ag listing under Group VIII misledsome later workers to think that missing elementswere being denoted (13). Acceptance of his table was

partly brought about by his astonishingly accuratepredictions of the properties of the then unknownscandium (shown as ‘–- = 44’ in Figure 3), gallium‘–- = 68’ and germanium ‘–- = 72’. Mendeleev’s pre-dictions also led to the subsequent discovery of otherelements including francium, radium, technetium,rhenium and polonium. Other factors such as thesuccessful accommodation or placement of the ele-ments were also important, a topic well discussed ina recent book (3).

It is apparent from Mendeleev’s tables that forhim (and others) the pgms, some of the transitionmetals, lanthanides and actinides then known poseda problem; here we concentrate on the pgms. Henoted their very similar properties and that therewere very small differences between the atomicweights of Ru-Rh-Pd and between those of Os-Ir-Pt (28). He knew that only Ru and Os demonstratedoctavalency in Group VIII (‘RO4’; R denotes an ele-ment), but includes Rh, Pd, Ir and Pt in GroupVIII. Mendeleev also placed iron, cobalt and nickel,and the coinage metals copper, silver and gold in

Fig. 2 William Odling’s table ofelements from 1864 (23)

Platinum Metals Rev., 2008, 52, (2) 117

Group VIII; he additionally accommodated thecoinage metals in Group I. His problems with all hisGroup VIII elements continued to trouble him: aslate as 1879 he published two papers in ChemicalNews which tried to address this difficulty (29, 30).In the first paper he split Groups I–VII into left-hand ‘even’ and right-hand ‘odd’ blocks, withGroup VIII in the centre, Cu, Ag and Au beingaccommodated in both VIII and the ‘odd’ I–VIIblock (29). In the second paper he ruefully refers toGroup VIII as ‘special’ and ‘independent’ (30).

Mendeleev published some thirty PeriodicTables and left another thirty unpublished (3), butthe 1871 one (Figure 3) (28) is his most successful:it is the definitive Periodic Table of the nineteenthcentury and the basis of all later ones. As late as1988, the leading inorganic textbook “AdvancedInorganic Chemistry”, by Cotton and Wilkinson(fifth edition) (31) shows Group VIII as containingthe nine elements Fe, Co, Ni and the pgms (Cu, Agand Au are designated as Group IB). It was only inthe sixth edition of 1999 that the modern form(Figure 4), in which the pgm vertical pairs are inGroups 8, 9 and 10, was used (32).

The Transuranic Congeners of thePlatinum Group Metals

The story now moves forward to the SecondWorld War, when there was discussion as towhether uranium, neptunium and plutonium were

appropriately placed in the fourth row of the tran-sition metals (using 6d orbitals), or were membersof a lanthanide-like series, the ‘actinides’, using 5forbitals. The latter view prevailed (33), and now allthe actinides (thorium to lawrencium inclusive) areknown. Indeed, elements up to and including 118are now established, with the exception of element117 (34). These elements are recognised by theInternational Union of Pure and AppliedChemistry (IUPAC), although only those up to 111have ‘official’ names (Figure 4) (35); see also (36).Mendeleev’s table (28) omits most of the lan-thanides and actinides and, of course, the noblegases which were not known when he made up histable. However, some 140 years earlier, his versionhad essentially contained the kernel of our modernPeriodic Tables.

Recent chemical work on a few very short-livedatoms of each element strongly suggests that ele-ments 104 to 111 are members of a fourthtransition metal series involving 6d orbitals. Thus104rutherfordium, 105dubnium, 106seaborgium and107bohrium have properties analogous to those ofhafnium (Group 4), tantalum (Group 5), tungsten(Group 6) and rhenium (Group 7) respectively.

The next three elements were all made in thelinear accelerator in the city of Darmstadt, Hessen,Germany. Hassium was first made in 1984, andnamed from the Latin ‘Hassias’ for the state ofHessen. Meitnerium was first made in 1982, and

Fig. 3 Mendeleev's Periodic Table of 1871 (28)

Platinum Metals Rev., 2008, 52, (2) 118

named after Lise Meitner (1878–1968), the dis-coverer of protactinium in 1917. Darmstadtiumwas first made in 1994, and named afterDarmstadt. For any meaningful chemistry to becarried out on a given element, at least four atomsare necessary, of half-life (t½) > 1 second, and aproduction rate of at least one atom per week isrequired. The nuclear reactions producing the ele-ments should give only single products. For thesethree elements the most useful nuclear reactionsare (Equations (i)–(iii)):

Of these, 269Hs and 270Hs have t½ = 14 and 23 srespectively; 266Mt has t½ = 6 × 10–3 s and 271Dt hast½ = 6 × 10–2 s, so at present chemistry can only becarried out on hassium. It is clearly a congener ofOs: using just seven atoms it was found to form avolatile tetroxide (37) which in alkaline NaOHgives a species which is probably cis-Na2[HsO4(OH)2] (38). For studies on meitneriumand darmstadtium to be made, longer-lived iso-topes are essential – they would also be much

more difficult to study chemically, since distinc-tive volatile Ir and Pt compounds are rare anddifficult to synthesise on a very small scale, unlikeHsO4, although the fluorides IrF6 and PtF6 arevolatile above 60ºC. It seems likely, however, thatthese three elements are congeners of Os, Ir andPt, particularly since it has recently been shownthat the unnamed (at the time of writing) element112 is itself volatile. This suggests that it is a con-gener of mercury (39), as would be expected ifelements 104–111 inclusive form a fourth transi-tion metal series.

ConclusionsThe story of the Periodic Table is convoluted,

and this article has concentrated on the pgms. Itis clear that they represented a challenge to themakers of the tables, but the problem was finallyresolved by Mendeleev some 140 years ago (28).The three man-made congeners of these ele-ments, hassium, meitnerium and darmstadtium,are likely to have chemistries similar to those ofosmium, iridium and platinum. At the time ofwriting it has been possible to demonstrate thisonly for hassium.

Fig. 4 The current Periodic Table (35) based on IUPAC recommendations

248Cm + 26Mg → 269, 270Hs + 5 or 4 1n (i)209Bi + 58Fe → 266Mt + 1n (ii)208Pb + 64Ni → 271Ds + 1n (iii)

96

83

82

12

26

28

108

109

110

0

0

0

Platinum Metals Rev., 2008, 52, (2) 119

AcknowledgementsI am grateful to Professor Christoph Düllmann

(Gesellschaft für Schwerionenforschung mbH,

Darmstadt, Germany) and Dr Simon Cotton(Uppingham School, Rutland, U.K.) for their adviceon aspects of transuranium chemistry.

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References

The AuthorBill Griffith is an Emeritus Professor of Chemistry at Imperial College, London. He has much experience with the platinumgroup metals, particularly ruthenium and osmium. He has published over 260 research papers, many describing complexesof these metals as catalysts for specific organic oxidations. He has written seven books on the platinum metals, and iscurrently writing another on oxidation catalysis by ruthenium complexes. He is the Secretary of the Historical Group of theRoyal Society of Chemistry.