Stable oxidation stales

In Ihis chapter the theories developed previously will be used 10 help correlate the important facts of the chemistry of groups 1—12 Much of the chemistry of these elements, in particular the transition metals, has already been included in the chapters on coordination chemistry (Chapters II, 12, and 13). More will be discussed in the chapters on organometaJlic chemistry (Chapter 15), clusters (Chapter 16), and the descriptive biological chemistry of the transition metals (Chapter 19). The present chapter will concentrate on the trends within the series (Sc to Zn, Y to Cd, Lu to Hg, La to Lu, and Ac to Lr), the differences between groups (Ti — Zr - Hf Cu — Ag - Au), and the stable oxidation stales of the various metals. 

Zinc(II), gallium(III), and germanium(IV) are the most stable oxidation stales for these elements, but the later nonmetals (arsenic, selenium, and bromine) show a reluctance to assume their highest possible oxidation stale. 

If a major breakthrough in nuclear synthesis were achieved, two elements that are hoped for are those with atomic numbers 114 and 164, both congeners of lead. Look at the extended periodic table in Chapter 14 and suggest properties (such as stable oxidation stales) for these two elements. How do you suppose their electronegativities will compare with those of the other Group IVA (14) elements - ... 

Cadmium has only one stable oxidation stale (+2) within the electrochemical window of water, but it forms several relatively slable compounds with oxygen and hydrogen, which differ in their degree of hydration and in their crystallographic structure. PZCs/IEPs of cadmium (hydr)oxides are presented in Tables 3.270 through 3.275. 

Table 6.1 The positive oxidation stales of the elements ol the s- and p-blocks that are stable in aqueous solution...

From Group 15 to Group 16. non-metallic behaviour takes over completely with no positive ions being stable. The + 6 state of sulfur is seen to have very poor oxidizing properties, and it is only in its concentrated form, and when hot, that sulfuric(VI) acid is a good oxidant. Hot concentrated sulfuric acid oxidizes metallic copper and is reduced to sulfur dioxide. The relative stabilities of the Se species with positive oxidation stales are considerably less than their S or Te counterparts, another example of the effect of the 3d contraction. 

CrOl ) reasonably stable the Cr(I) oxidation stale is practically unknown. For both Cu2 and Cr3 (as well as many other transition metal ions) ligand field effects in their complexes (see Chapter II) are much more important in determining stable oxidation states than are electron configurations. 

The lower oxidation stales of niobium and tantalum arc unimportant compared to the + suite. Because of the general insolubility of the oxides, md (he lack of stable lower oxidation slates, there is little solution redox chemistry. Niohium(UE) does appear to form upon the reduction of niobium V) with zinc, and is stable in the cold in the absence of air, but if the solution is heated, decomposition occurs with precipitation of mixed oxides. 

Effect on V V remains in +5 oxidation slate where it is most mobile and most acidic. Severe zeolite allacfc. V cycles between +5 and +3 oxidation stales. Lower V mobility and less severe zeolite attack. V in (he +3 state can react to form stable vanadates V cycles between +5 and +3 oxidation states. Lower V mobility and less severe zeolite attack. V in the +3 state can react to form stable vanadates. 

The Group VIllB (8, 9, and 10) metals illustrate well the point made previously that heavier congeners more readily assume higher oxidation states. Thus iron, cobalt, and nickel are effectively limited to +2 and i-3 oxidation stales, but all of their congeners have reasonably stable higher oxidation states. 

There is a definite tendency for the nonmetals of the fourth row—As, Se. and Br—to be unstable in their maximum oxidation stale. For example, the synthesis of arsenic pentachloride eluded chemists until comparatively recently.29 although both PCI, and SbCI, arc stable. The only stable arsenic penlahatide is AsF, AsCI, decomposes at -SO °C. and AsBr, and Asl, are still unknown. 

Table 8.7 Oxidation stales of the actinide elements those in red are Ihe most stable states in aoueous solution in the absence of dioxygen...

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