Group 13 elements aqueous chemistry

The chemistry of hafnium has not received the same attention as that of titanium or zirconium, but it is clear that its behaviour follows that of zirconium very closely indeed with only minor differences in such properties as solubility and volatility being apparent in most of their compounds. The most important oxidation state in the chemistry of these elements is the group oxidation state of +4. This is too high to be ionic, but zirconium and hafnium, being larger, have oxides which are more basic than that of titanium and give rise to a more extensive and less-hydrolysed aqueous chemistry. In this oxidation state, particularly in the case of the dioxide and tetrachloride, titanium shows many similarities with tin which is of much the same size. A large... 

Fig.1 Latimer diagram for the aqueous chemistry of the group 5 elements.

Latimer diagrams are available for all the elements except for the unreactive lighter members of Group 18, and form an excellent and concise summary of the aqueous chemistry of such elements. They are used extensively in Chapters 6, 7 and 8. The diagrams used so far in the text consist of one line, but it is sometimes instructive to link oxidation states that are not adjacent to each other and to include the reduction potential appropriate to those states. One example is given in Figure 5.2 for some of the states of iron at pH = 0. 

The subject of this chapter is the periodicity of the aqueous chemistry of the elements of the s-block (Groups 1 and 2) and the p-block (Groups 11-18) of the Periodic Table. Modified Latimer diagrams summarize the chemistry of all the elements, and some volt-equivalent diagrams are given to represent the inter-relations between various oxidation states of the elements. Explanations of some trends in redox chemistry are discussed in detail. 

One of the classical properties of the main group elements is that the stability of the lower oxidation states increases with atomic number, and the chemistry of thallium is a good example of this effect. In aqueous solution, the Tl+ ion is stable with respect to oxidation by the solvent and there is accordingly an extensive chemistry of this oxidation state. The similarities between Tl+ and the corresponding alkali metal cations have resulted in much interest in the use of this ion as a probe in biochemical systems, and the ease with which 205T1 NMR spectra can be recorded has also had an impact on such studies.277,278... 

The aqueous chemistries of the Group 4 elements in seawater are those of strongly hydrolysed elements. Although the hydrolysis behaviour of these elements is not well characterised, a review of available data (Baes and Mesmer, 1976) indicates that the dominant chemical form of Ti in seawater should be Ti(OH)4, while for Zrw and HfIV, significant forms include both M(OH)J and M(OH) 5. Observed seawater concentrations of Zr are similar to saturation levels (Baes and Mesmer, 1976) predicted for equilibrium with Zr02(s). 

We discuss in this chapter the elements of the first transition series, titanium through copper. There are two main reasons for considering these elements apart from their heavier congeners of the second and third transition series (1) in each group (e.g., V, Nb, and Ta) the first-series element always differs appreciably from the heavier elements, and comparisons are of limited use, and (2) the aqueous chemistry of the first-series elements is much simpler, and the use of ligand field theory in explaining both the spectra and magnetic properties of compounds has been far more extensive. 

Inorganic Chemistry of the Main-group Elements as some enthalpies of dilution have been carried out in a reaction calorimeter.170 These results have been combined with some earlier data to obtain the enthalpy of solution of HF as a function of composition, between HF,ooH20 and HF,H20. Vasil ev and Kozlovskii171 have also determined some heats of dilution of aqueous HF calorimetrically as well as heats of neutralization, H++F —> HF, and reaction, H+ + 2F — HF2. There are also some new values of the equilibrium constants for these two reactions.172 Russian workers have also investigated the same equilibria, with aqueous dioxan as solvent.173 Vaillant et al. have redetermined the acidity function for the HF-H20 system for a range of composition.174 Russian workers have reported solubility data for MF3 (M = Eu, Tb, Dy, or Ho)175 and some hexafluorostannates176 in aqueous HF. 

Table 1 shows some oxides and halides of the 3d series elements, selected to show the range of stable oxidation states. These follow the same trends as found in aqueous chemistry (see Topic H3). Elements early in the series form compounds up to the group oxidation state, for example, Ti02,... 

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