Oxidation block elements

FIGURE 4. Medium-long form table showing highest and most common oxidation states of the d-block elements. Only two of these 30 ions, Ag+1 and Au+3, (shown in bold-face) show anomalous electronic configurations with respect to other ions in the same groups. 

All elements in the s block are reactive metals that form basic oxides. The p-block elements tend to gain electrons to complete dosed shells they range from metals through metalloids to nonmetals. 

All d-block elements are metals with properties between those ofs-block and p-block metals. Many d-block elements form cations in more than one oxidation state. 

Metals form basic oxides, nonmetals form acidic oxides the elements on a diagonal line from beryllium to polonium and several d-block metals form amphoteric oxides. 

Hydrogen sulfide dissolves in water to give a solution of hydrosulfuric acid that, as a result of its oxidation by dissolved air, slowly becomes cloudy as S8 molecules form and then coagulate. Hydrosulfuric acid is a weak diprotic acid and the parent acid of the hydrogen sulfides (which contain the HS ion) and the sulfides (which contain the S2 ion). The sulfides of the s-block elements are moderately soluble, whereas the sulfides of the heavy p- and d-block metals are generally very insoluble. 

The range of oxidation states of a d-block element increases toward the center of the block. Compounds in which the d-block element has a high oxidation state tend to be oxidizing those in which it has a low oxidation state tend to be reducing. The acidic character of oxides increases with the oxidation state of the element. 

Three other compounds of s-block elements—calcium oxide (CaO, known as lime ), sodium hydroxide (NaOH), and sodium carbonate (Na2 CO3)—are among the top 15 industrial chemicals in annual production. Lime is perennially in the top 10 because it is the key ingredient in construction materials such as concrete, cement, mortar, and plaster. Two other compounds, calcium chloride (CaCl2 ) and sodium sulfate (Na2 SO4 ), rank just below the top 50 in industrial importance. 

Although zinc is formally a 4-block element, some of its chemical properties are similar to those of the alkaline earth metals, especially those of magnesium. This is mainly due to zinc s exclusive exhibition of the +2 oxidation state in all its compounds and its appreciable electropositive character. With a standard potential of —0.763 V, zinc is considerably more electropositive than copper and cadmium. 

The development of G. N. Lewis s octet rule for the s/p-block elements was strongly influenced by the stoichiometric ratios of atoms found in the common compounds and elemental forms (CH4, CCI4, CO2, CI2, etc.). Let us therefore begin analogously by examining the formulas of the common neutral binary chloride, oxide, and alkyl compounds of transition metals. (Here we substitute alkyl groups for hydrogen because only a small number of binary metal hydrides have been well characterized.)... 

The Frost diagrams for the first series of the d block elements in acidic solution, pH = 0, given in Figure 7.11(b) show many similarities with the variation of the enthalpy of formation of the oxides. Only the oxidation states observed for solid oxides are included. 

Table 10 Molybdates, tungstates, and mixed-oxide compounds of molybdenum-(vi) and tungsten (vi) with s-, p-, and d-block elements...

The ierms valency and oxidation slale were defined and exemplified by reference lo ihc s- and p-block elements. 

This chapter consists of a description of the ions formed in aqueous solutions by the transition elements - the d-block elements - and a discussion of the variations of their redox properties across the Periodic Table from Group 3 to Group 12. There is particular emphasis on the first transition series from scandium to zinc in the fourth period, with summaries of the solution chemistry of the second (Y to Cd) and third (Lu to Hg) series. The d-block ions in solution are those restricted solely to aqua complexes of cations, e.g. [Fe(H20)f,]" +, and the various oxocalions and oxoanions formed, e.g. V02+ and MnCXj". Oxidation states that are not well characterized are omitted or referred to as such. 

The transition from positive ions with low oxidation states, via insoluble oxides with intermediate oxidation states, to oxoanions with high oxidation states, is caused by the competition between ionization energies, lattice enthalpies and enthalpies of hydration, similar to the discussion of the variations of ionic forms of the p-block elements given in Section 6.1. Further discussion occurs in Section 7.5.3. 

Clearly different ligand types will favor different oxidation states. Higher oxidation states prefer hard acid donor atoms, generally first-row p-block elements, rich in electron density and capable of strong a donation. A further provision is that they should resist oxidation. Common donor chromophores which have been used are amines N, imides (including oximes and imines)I>N , oxides —0 and fluorides F-. Second- and third-row p-block donors have also been used, forming bonds which are more covalent in character and creating special problems, as discussed below. 

Most metallic main-group elements form basic oxides and most nonmetallic elements form acidic oxides. Elements close to the diagonal frontier between metals and nonmetals form amphoteric oxides, as do some of the d-block elements. 

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