The d-Block Elements

1 The Latimer diagram for vanadium in basic solution is provided in Resource Section 3. The reduction potential for O2/H2O couple in alkaline solution is  

The reduction potential for VOA 203 couple in the basic solution is -0.486V. The potential difference for oxidation of VO to V2O3 with oxygen is 

VO will be oxidized to V2O3 by oxygen in air. The next oxidation step is oxidation from V2OJ to HV205 with reduction potential +0.542V. This reaction has the following potential difference  

This step has a negative potential and is not a thermodynamically spontaneous process. This means that a basic solution oxidation of VO to V2O is a thermodynamically favourable process, and V2O3 is more stable than VO in presence of oxygen. 

2 RcsCI is a trimer (see Structure 19). When ligands are added, such as PPhj, discrete molecular species such as RejCl9(PPh3)3 are formed (see below). Sterically, the most favourable place for each bulky triphenylphosphine ligand to go is in the terminal position in the Rc3 plane. 

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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. 

Because the metallic radii of the d-block elements are all similar, they can form an extensive range of alloys with one another with little distortion of the original crystal structure. An example is the copper-zinc alloy used for some copper coins. Because zinc atoms are nearly the same size as copper atoms and have simi-... 

The incompletely filled d-subshell is responsible for the wide range of colors shown by compounds of the d-block elements. Furthermore, many d-metal compounds are paramagnetic (see Box 3.2). One of the challenges that we face in this chapter is to build a model of bonding that accounts for color and magnetism in a unified way. First, though, we consider the physical and chemical properties of the elements themselves. 

The shapes of the d-orbitals affect the properties of the d-block elements in two ways (see Fig. 1.37) ... 

FIGURE 16.4 The atomic radii of the d-block elements (in picometers). Notice the similarity of all the values and, in particular, the close similarity between the second and the third rows as a result of the lanthanide contraction. 

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. 

Although the physical properties of the d-block elements are similar, the chemical properties of these elements are so diverse that it is impossible to summarize them fully. We can, however, observe some of the major trends in properties within the d block by considering the properties of certain representative elements, particularly those in the first row of the block. 

TABLE 16.1 Properties of the d-Block Elements Scandium Through Nickel... 

Many of the d-block elements form characteristically colored solutions in water. For example, although solid copper(II) chloride is brown and copper(II) bromide is black, their aqueous solutions are both light blue. The blue color is due to the hydrated copper(II) ions, [Cu(H20)fJ2+, that form when the solids dissolve. As the formula suggests, these hydrated ions have a specific composition they also have definite shapes and properties. They can be regarded as the outcome of a reaction in which the water molecules act as Lewis bases (electron pair donors, Section 10.2) and the Cu2+ ion acts as a Lewis acid (an electron pair acceptor). This type of Lewis acid-base reaction is characteristic of many cations of d-block elements. 

Explain trends in chemical and physical properties among the d-block elements (Sections 16.1 and 16.2). 

The elements that can form cations relatively easily are metals. All metals have similar properties, in part because their outermost s electrons are relatively easy to remove. All elements in the s block have ns or n s valence configurations. The d-block elements have one or two n S electrons and various numbers of (n - 1) d electrons. Examples are titanium (4 S 3 d ) and silver (5 Ad ). Elements in the f block have two S electrons and a... 

Because the low-energy electronic configurations of d-block elements and their +1 ions are invariably of sdm form (see Table 2.2, Section 2.8), it is clear that both s and d orbitals will be involved in bond formation at transition-metal centers. What is less clear, a priori, is what role the valence p orbitals will play in bonding of the d-block elements. 

The general procedure for constructing Lewis-like diagrams for transition-metal species can best be illustrated by representative examples. From Table 4.1 one can recognize that the first transition series (Sc-Zn) includes a disproportionate number of exceptional cases compared with later series, and illustrative examples will therefore be drawn primarily from the third transition series (La-Hg). (The somewhat anomalous behavior of the first transition series and general vertical trends in the d-block elements will be discussed in Section 4.10.)... 

From the polarities of the maximum-valency MH NBOs, one can infer the natural electronegativity Xm(N) of each transition metal M, following the procedure outlined in Section 3.2.5. For cases in which two or more inequivalent M—H bonds are present (e.g., RcH ), we employ the average value of cm2 (or of the bond ionicity z mh) to evaluate xm(N) from Eq. (3.60). Table 4.7 presents the natural electronegativity values for all three series of the d-block elements. 

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