Other Chemical Properties

This chapter covers a number of concepts or properties that did not relate to material discussed in earlier chapters. Some of these techniques are seldom needed. Others just do not merit a chapter of their own because they are easy to apply. 

The first section of this chapter discusses various ways that chemical properties are computed. Then a number of specific properties are addressed. The final section is on visualization, which is not so much a property as a way of gaining additional insight into the electronic structure and motion of molecules. 

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The physical and chemical properties of the elements show regular periodic trends that can be explained using electron configurations and nuclear charges. We focus on the physical properties of the elements in this section. A preliminary discussion of the chemical properties of some of the elements appears in Section Other chemical properties are discussed after we introduce the principles of chemical bonding in Chapters 9 and 10. 

Electrochemistry provides routes to directly prepare nanostructures both delocalized in a random or organized way and localized at predefined surface sites with adjustable aspect ratios. Purity, monodispersity, ligation, and other chemical properties and treatments are definitely important in most cases. By delocalized electrodeposition it is possible to decorate large areas of metal or semiconductor surfaces with structures of a narrow size distribution stable nuclei-clusters can be... 

Fig. 1.2 Properties revealed by low-energy exchanges belong to the molecular phenotype , as exemplified here. This is contrasted with some other chemical properties (e.g. reactivity) which involve the...

Explain in terms of molecular structure the following trend in solubilities of the gases in water C2H2 > > C2H4 > C2H6. How does the trend in solubility reflect other chemical properties ... 

Although even the smaller structural units of zeolites are large enough to tax the most advanced quantum chemical computational methods to their limits, nevertheless, it is now possible to determine the fundamental electronic properties of zeolite structural units. In addition to their unique geometrical (in fact, topological) properties, the electronic structure and charge distribution of zeolites are of fundamental importance in explaining their catalytic and other chemical properties. 

One final comment on the Fe/E O system is needed if Fig. 15.3 were extended beyond pH 14, we would have to include the stability fields of Fe(OH)4 (aq) and Fe(OH)3 (aq).12 In other words, iron, like aluminum, chromium, zinc, and many other metals, exhibits amphoteric behavior (i.e., has both acidic and base like properties), but only if a sufficiently wide range of pH is considered. Amphoteric behavior, like many other chemical properties, is not so much something that a given element does or does not exhibit, but rather is a trait that different elements display to different extents. 

To shed more light on the structure of DNA, Rosalind Franklin and Maurice Wilkins used the powerful method of x-ray diffraction (see Box A-A) to analyze DNA fibers. They showed in the early 1950s that DNA produces a characteristic x-ray diffraction pattern (Fig. 8-14). From this pattern it was deduced that DNA molecules are helical with two periodicities along their long axis, a primary one of 3.4 A and a secondary one of 34 A The problem then was to formulate a three-dimensional model of the DNA molecule that could account not only for the x-ray diffraction data but also for the specific A = T and G = C base equivalences discovered by Chargaff and for the other chemical properties of DNA. 

Zeolites containing transition metal ions (such as Cr3+, Ag+, and Cu2 + ) are active as oxidation catalysts. Comprehensive reviews dealing with various aspects of the structure (34-37) sorption (35), catalysis (38-42), and other chemical properties of zeolites are available in the literature. 

The chemical properties of thioarsenates are largely unknown, but are expected to be different than the properties of thioarsenites or other arsenic species (Wallschlager and Stadey, 2007), 3880. If thioarsenates are prominent in sulfide-rich and anoxic environments, measurements of their sorption and other chemical properties are required to understand and predict their mobility in natural environments. 

On the other hand, the enumerated structures themselves might be useful as input for other computer programs that generate computational data, such as QSAR or other chemical property predictions. Since these programs accept and work on individual specific structures, these structures must be generated both for input to these programs and for association with their output. This capability is important for the process of designing new combinatorial libraries. 

Equation 2.40 shows that the solvent power (as measured by 6) of an SF is governed by two factors (25). First, it is regulated by the liquid value 8Viq (see Table 2.1), reflecting the polarity and other chemical properties of molecules of the parent liquid. Highly polar substances like ammonia would thus yield high 8s. By contrast, small relatively nonpolarizable species like helium have negligible solvent effects under any circumstances. 

An alternate approach makes use of a group contribution analysis (7.9j approach. The group contribution analysis method has proved useful for the determination of solubility parameters (12.13L and has provided an approach for a host of other chemical properties (14). In a group contribution analysis, each moiety in the chemical or polymer contributes additively to the property in question. 

Acidiiy. bawHy. am) other chemical properties depend on other factors in addition to clec-tromgaiivuy. Nevertheless, variation in eleetronegativiiy is iinportQnt in delcnniiung Ihese properties. 

Thus sodium chloride has the property of changing into a soft metal, sodium, and a greenish-yellow gas, chlorine, when it is decom-posed by electrolysis. It also has the property, when it is dissolved in water, of producing a white precipitate when a solution of silver nitrate is added to it and it has many other chemical properties. Iron has the property of combining readily with the oxygen in moist air, to form iron rust whereas an alloy of iron with chromium and nickel (stainless steel) is found to resist this process of rusting. It is evident from this example that the chemical properties of materials are important in engineering. 

Figure 2 Plot of Ga/Ni versus Ir/Ni showing bulk compositions of chondrites in nine groups (vvvvScott and Newsom, 1989). Each group is well resolved. The proportions of these siderophiles are not correlated with other chemical properties showing that the chemical variations in chondrites are complex (reproduced by permission of Verlag der Zeitschrift fiir Naturforschuang from Z. Naturforsch., 1989, 44a, 927).

Lutetium reacts slowly with water and dissolves in acids. Other chemical properties tend to be of interest only to researchers. 

Like acidity and basicity, other chemical properties, too, depend upon molecular structure. Indeed, most of this book will be concerned with finding out what this relationship is. 

The automatic synthesis of molecules, described in the previous section, attempts to generate feasible candidates without resorting to the detailed, fragmented, often informal, but nevertheless sound and valuable knowledge possessed by the human designer. The search for new molecules is carried out efficiently, but it is entirely built on a limited amount of knowledge, which is represented by the sets of constraints on (1) physical properties, (2) the feasibility of molecular structures, and (3) chemical stability and other chemical properties of the resulting molecules. 

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