Oxidation states transition elements

All decomposition reactions are endothermal except that of FeU04, presumably because this is the only reaction which involves oxidation of the double oxide. No significant diflFerence was noted in the DTA or TGA curves of the two NiU04 phases. It is interesting to note the alternating pattern in the decomposition reactions of the uranates. The iron, nickel, and zinc double oxides tend to decompose directly into their constituent oxides, while the manganese, cobalt, and copper compounds decompose to other double oxides. The pattern is not carried over into the decomposition temperatures. In this instance, the thermal stability of the double oxides appears to vary directly with the characteristic transition element oxidation states Gr(III) > Mn, Go (III, II) > Ni, Zn(II) > Gu(II, I). The iron compounds constitute a definite exception to this pattern. 

FIGURE 20.6 Common oxidation states for first-series transition elements. The states encountered most frequently are shown in red. The highest oxidation state for the group 3B-7B metals is their periodic group number, but the group 8B transition metals have a maximum oxidation state less than their group number. Most transition elements have more than one common oxidation state. 

Poster 32. B.S. Kim, D.Y. Lee, M.W. Oh, S.D. Park, H.W. Lee, W.S. Chung and T. Ishii (Korea Electrotechnology Research Institute, Pusan National University, Kagawa University) Comparison of Electronic State Calculation and Experimental Results of Electrical Conductivity of Mn-X(transition elements) Oxide by Anodic Deposition... 

A FIGURE 24.4 First-Row Transition Metal Oxidation States The transition metals exhibit many more oxidation states than the main-group elements. These oxidation states range from -1-7 to -H. 

The transition elements are often said to exhibit variable valency. Because they so readily form complex compounds, it is better to use the term variety of oxidation states . The states usually found for the elements Sc-Zn are ... 

Some of the oxidation states given above, especially the higher oxidation states (7, 6) and oxidation state 0, are found only when the metal atom or ion has attached to it certain groups or ligands. Indeed the chemistry of the transition elements is so dominated by their tendency to form coordination complexes that this aspect of their behaviour must be considered in some detail. 

Scandium is not an uncommon element, but is difficult to extract. The only oxidation state in its compounds is -I- 3, where it has formally lost the 3d 4s electrons, and it shows virtually no transition characteristics. In fact, its chemistry is very similar to that of aluminium (for example hydrous oxide SC2O3, amphoteric forms a complex [ScFg] chloride SCCI3 hydrolysed by water). 

In this oxidation state the titanium atom has formally lost its 3d and 4s electrons as expected, therefore, it forms compounds which do not have the characteristics of transition metal compounds, and which indeed show strong resemblances to the corresponding compounds of the lower elements (Si, Ge, Sn, Pb) of Group IV—the group into which Mendeleef put titanium in his original form of the periodic table. 

Like iron and the next transition element, nickel, cobalt is not generally found in any oxidation state above + 3, and this and + 2 are the usual states. The simple compounds of cobalt(III) are strongly oxidising ... 

These elements formed Group IIB of Mendeleef s original periodic table. As we have seen in Chapter 13, zinc does not show very marked transition-metaf characteristics. The other two elements in this group, cadmium and mercury, lie at the ends of the second and third transition series (Y-Cd, La-Hg) and, although they resemble zinc in some respects in showing a predominantly - - 2 oxidation state, they also show rather more transition-metal characteristics. Additionally, mercury has characteristics, some of which relate it quite closely to its immediate predecessors in the third transition series, platinum and gold, and some of which are decidedly peculiar to mercury. 

Reference has been made already to the existence of a set of inner transition elements, following lanthanum, in which the quantum level being filled is neither the outer quantum level nor the penultimate level, but the next inner. These elements, together with yttrium (a transition metal), were called the rare earths , since they occurred in uncommon mixtures of what were believed to be earths or oxides. With the recognition of their special structure, the elements from lanthanum to lutetium were re-named the lanthanons or lanthanides. They resemble one another very closely, so much so that their separation presented a major problem, since all their compounds are very much alike. They exhibit oxidation state -i-3 and show in this state predominantly ionic characteristics—the ions. 

Evidence other than that of ion-exchange favours the view of the new elements as an inner transition series. The magnetic properties of their ions are very similar to those of the lanthanides whatever range of oxidation states the actinides display, they always have -1-3 as one of them. Moreover, in the lanthanides, the element gado-... 

The actinide elements exhibit uniformity in ionic types. In acidic aqueous solution, there are four types of cations, and these and their colors are hsted in Table 5 (12—14,17). The open spaces indicate that the corresponding oxidation states do not exist in aqueous solution. The wide variety of colors exhibited by actinide ions is characteristic of transition series of elements. In general, protactinium(V) polymerizes and precipitates readily in aqueous solution and it seems unlikely that ionic forms ate present in such solutions. 

Vanadium, a typical transition element, displays weU-cliaractetized valence states of 2—5 in solid compounds and in solutions. Valence states of —1 and 0 may occur in solid compounds, eg, the carbonyl and certain complexes. In oxidation state 5, vanadium is diamagnetic and forms colorless, pale yeUow, or red compounds. In lower oxidation states, the presence of one or more 3d electrons, usually unpaired, results in paramagnetic and colored compounds. All compounds of vanadium having unpaired electrons are colored, but because the absorption spectra may be complex, a specific color does not necessarily correspond to a particular oxidation state. As an illustration, vanadium(IV) oxy salts are generally blue, whereas vanadium(IV) chloride is deep red. Differences over the valence range of 2—5 are shown in Table 2. The stmcture of vanadium compounds has been discussed (6,7). 

Cu ( j -C5H5)2] is not. Likewise, Fe and Ni carborane derivatives are extremely stable. Conversely, metallocarboranes tend to stabilize lower oxidation states of early transition elements and complexes are well established for Ti", Zr , Hf , V , Cr and Mn" these do not react with H2, N2, CO or PPh3 as do cyclopentadienyl derivatives of these elements. 

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