BONDS IN MOLECULES AND CRYSTALS

A glance at the Periodic Table will show the difficulty of making useful generalizations about bonding in many inorganic compounds. In Table 7.1 the full lines enclose elements which form ions stable in aqueous solution. At the extreme right the anions include only the halide ions combines with HjO to form (2) 

and H combines with H2O to form However, exists in many 

The metals which form cations include the most electropositive elements at the left of the Table and a group of 3d metals in their lower oxidation states (usually 2 or 3), together with some of the earlier B subgroup metals, Tl(i) and Pb(ii) note that Pb is known only in crystalline oxides and oxy-compounds. In the lower centre of the Table is a group of metals which have no important aqueous ionic chemistry and probably not much tendency to form ions in the crystalline state-though the bonds in certain oxy- and fluoro-compounds may well have appreciable ionic character (for example, dioxides such as M0O2, lower fluorides such as M0F3, etc.). 

The Group IVA metals have no important aqueous ionic chemistry but form ions in crystalline oxy-compounds. Bismuth can perhaps be grouped with Ti, Zr, and Hf it has a strong tendency to form hydroxy-complexes, but salts such as Bi(N03)3. 5 H2O, M3 [Bi(N03)6] 2 24 H2O, and 812(804)3 presumably contain Bi ions. It seems reasonable to put Ga(iii), In(iii), Tl(iii), and Sn(ii) in this group the complex structural chemistry of these elements is outlined in Chapter 26. 

In Group IV there is a change from the essentially covalent 4-coordinated structure of diamond. Si, Ge, and grey Sn(iv) through white Sn(ii) to Pb, with a c.p. structure characteristic of many metals. Group V begins with the normal molecular structure of N2 and white P (P4), but phosphorus also has the deeply 

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Bonds in Molecules and Crystals halogen.) The QO2 ion exists in CIO2 (AsFg), formed from CIO2F and AsFs,... 

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