ABSTRACT
FIG. 14.1 Oxidation state free energy diagrams of the first transition series elements, it is clear that the Group oxidation state becomes increasingly unstable towards manganese. Thereafter, all states above III are unstable, and the variation in the relative stability of the II and III states (and I for copper) is of most importance. (Compare Section 8.6.)
The lists of the oxides and halides and the free energy diagrams give largely complementary pictures of the stabilities of the various oxidation states, in the solid state and in aqueous solution respectively. At titanium, the Group oxidation state of IV is the most stable and the lower states become increasingly reducing. Moving along the series, the Group oxidation state becomes more unstable and more oxidizing so that, at manganese, only a few compounds of the VII state are known and all are strongly oxidizing. Beyond manganese, the Group state disappears and only a few, unstable, strongly oxidizing states greater than III exist. Among the lower states, either the II or the III state is the most stable state from chromium onwards, and the relative stability of these two states varies with the number of d electrons as was indicated in the last chapter, with the II state finally becoming the most stable at nickel and copper. This variation in stability is shown up in the free energy diagrams by the increasing height above zero of the Group state up to manganese, and by the increasing instability of the III state at the right of the figure. (See also Section 14.10.)
14.2.1 Titanium(IV) 315 14.2.2 Titanium(lll) and lower
oxidation states 317
14.3 VANADIUM, 3d34s? 318 14 3 1 Vanadium(V) 319 1 4 3 2 VanadiumOV) 322 1433 Vanadium(lll) 323
14.4 CHROMIUM, 3d54s* 324 1 4 4 1 Chfomium(VI) 325 1 4 4 2 Chromium(V) and
chromium (IV) 325 14.4.3 Chromium(lll) 327 14.4.4 Chromium(ll) and lower
oxidation states 328
14.5 MANGANESE, 3dV 329 1 4 5 1 The high oxidation states.
