Inert-pair effects

The steady trend towards increasing stability of rather than M compounds in the sequence Ge, Sn, Pb is an example of the so-called inert-pair effect which is well established for the heavier post-transition metals. The discussion on p. 226 is relevant here. A notable exception is the organometallic chemistry of Sn and Pb which is almost entirely confined to the state... 

Although both aluminum and indium are in Group 13/III, aluminum forms A1J+ ions, whereas indium forms both In3+ and In+ ions. The tendency to form ions two units lower in charge than expected from the group number is called the inert-pair effect. Another example of the inert-pair effect is found in Group 14/IV tin forms tin(IV) oxide when heated in air, but the heavier lead atom loses only its two p-electrons and forms lead(II) oxide. Tin(II) oxide can be prepared, but it is readily oxidized to tin(IV) oxide (Fig. 1.56). Lead exhibits the inert-pair effect more strongly than tin. 

The inert-pair effect is the tendency to form ions two units lower in charge than expected from the group number it is most pronounced for heavy elements in the p block. 

Identify which of the following elements experience the inert-pair effect and write the formulas for the ions that they form (a) Sb (b) As (c) Tl (d) Ba. 

Many metallic elements in the p and d blocks, have atoms that can lose a variable number of electrons. As we saw in Section 1.19, the inert-pair effect implies that the elements listed in Fig. 1.57 can lose either their valence p-electrons alone or all their valence p- and s-electrons. These elements and the d-block metals can form different compounds, such as tin(II) oxide, SnO, and tin(IV) oxide, Sn02, for tin. The ability of an element to form ions with different charges is called variable valence. 

Group 13/III is the first group of the p block. Its members have an ns np1 electron configuration (Table 14.5), and so we expect a maximum oxidation number of +3. The oxidation numbers of B and A1 are +3 in almost all their compounds. However, the heavier elements in the group are more likely to keep their s-electrons (the inert-pair effect, Section 1.19) so the oxidation number +1 becomes increasingly important down the group, and thallium(I) compounds are as common as... 

The first three members of this series appear at the bottom of the B subgroups of the periodic groups 4, 3 and 2. They exhibit the so-called inert-pair effect and normally assume oxidation states of -l-4,-l-2 -l-3,-f-1 and -1-2,0 respectively, i.e. differing by two units. The species Hg" ", TF" and Pb are of high energy and... 

In the past 15 years a large number of polonium compounds have been prepared in visible quantities for the first time and as a result of these investigations it has been shown that polonium behaves chemically very much as would be expected from its position in the Periodic Table, with the inert-pair effect, likely to be more marked in polonium than in tellurium, still little in evidence. 

In acidic solution In and Tl have + 1 states, consistent with the inert pair effect that affects the heavier elements of Groups 13 to 15. 

Valencies and oxidation slates that vary from those expected from the operation of the octet rule were explained hypervalency and the inert pair effect were described. 

The formation of compounds in the formal oxidation state of VI is well established for all four elements, for example, the sexivalent fluorides and the TeF ion. However, oxidation to this highest valency state becomes progressively more difficult as group VIB is descended since the inert pair effect causes the elements to behave as though two of their valence electrons are absent. Some examples of the compounds formed by the group VIB elements and their stereochemistries are described in Table 1. 

Finally, the heavier posttransition metals have group number oxidation states corresponding to < 10 configurations indium(lll), thallium(III), tin(IV), lead(lV), anti-mony(V). bismuth(V), etc. However, there is an increasing tendency, termed the inert pair effect," for the metals to employ p electrons only and thus to exhibit oxidation states two less than those given above (see Chapter 18). 

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