Network solids properties

The elements that form network solids lie on the right side of the periodic table, bordering the elements that form molecular crystals on one side and those that form metals on the other. Thus they are intermediate between the metals and the nonmetals. In this borderline region classifications are sometimes difficult. Whereas one property may suggest one classification, another property may lead to a different conclusion. Figure 17-3 shows some elements that form solids that are neither wholly metallic nor wholly molecular crystals. 

Distinguish metallic solids, ionic solids, network solids, and molecular solids by their structures and by their properties (Sections 5.8-5.11 and 5.14). 

Moreover, the curves of 2.0 and 5.0 phr TAC, have a more hnear relationship compared with those crosslinked with DCP alone or in the presence of 0.5 phr TAC. This strongly suggested that at higher TAC concentrations, a more rigid network was present which restricted the ability of samples to swell. The results also give further evidence that gel content is not really a suitable parameter to evaluate solid properties when using TAC in the crosslinking system. 

A wide range of properties can be found among network solids. 

The nature of the bonds between the structural units of crystalline solids impart other physical properties to these solids. Metals are good conductors of electricity because metallic bonds allow a free flow of electrons. Covalent network, molecular, and ionic solids do not conduct electricity because their bonds do not provide for mobile electrons. Remember, however, that ionic solids in a water solution have free electrons and are good conductors of electricity. Metallic solids are malleable and ductile covalent network solids are brittle and hard. These differences in physical properties are caused by the chemical bonds between the units It is all in the bonds ... 

Coordination polymers are infinite network solids made up of metals and ligands. They can be either discrete or 1-3 D and can have interesting and tuneable magnetic and themal expansion properties. 

A third approach arises when pursuing primarily structural objectives is coupled with keen observation, and examination and testing of the properties of materials synthesized. A simple example involves the common situation in which solvent molecules are incorporated into cavities in network solids. Further examination to see if the solvent can be removed or replaced by other guests is often... 

Crystalline solids can be classified into five categories based on the types of particles they contain atomic solids, molecular solids, covalent network solids, ionic solids, and metallic solids. Table 13-4 summarizes the general characteristics of each category and provides examples. The only atomic solids are noble gases. Their properties reflect the weak dispersion forces between the atoms. 

Covalent network solids Atoms such as carbon and silicon, which can form multiple covalent bonds, are able to form covalent network solids. In Chapter 7, you learned how the structures of graphite and diamond give those solid allotropes of carbon different properties. Figure 13-20 shows the covalent network structure of quartz. Based on its structure, will quartz have properties similar to diamond or graphite ... 

Molecule-based materials exhibiting cooperative physical properties constitute one of the most active areas of interest in contemporary materials chemistry and science. An attractive chemical feature of these materials is the synthetic versatility provided by molecular chemistry. From the point of view of the physical properties, molecule-based materials can exhibit the properties of interest usually associated with the inorganic network solids, " as for example, high DC metal-like electrical conductivity and superconductivity, ferromagnetism, and non-linear optical responses. ... 

There are some solids, often called covalent network solids, that are composed only of atoms interconnected by a network of covalent bonds. Quartz and diamond are two common examples of network solids. In contrast to molecular solids, network solids are typically brittle, nonconductors of heat or electricity, and extremely hard. Analyzing the structure of a diamond explains some of its properties. In a diamond, each carbon atom is bonded to four other carbon atoms. This tetrahedral arrangement, which is shown in Figure 8.25, forms a strongly bonded crystal system that is extremely hard and has a very high melting point. 

What is the difference between a covalent molecular solid and a covalent network solid Do their physical properties differ Explain your answer. 

Skill 22.6 Classify unknown solids as molecular, metallic, ionic, and covalent network solids according to their physical and chemical properties. 

Most metals are malleable, which means that they can be hammered into thin sheets, and ductile, which means that they can be drawn into wires ( FIGURE 12.10). These properties indicate that the atoms are capable of slipping past one another. Ionic and covalent-network solids do not exhibit such behavior. They are typically brittle and fracture easily. Consider, for example, the difference between dropping a ceramic plate and an aluminum cooking pan onto a concrete floor. 

Both covalent-network solids and ionic solids can have melting points well in excess of room temperature, and both can be poor conductors of electricity in their pure form. However, in other ways their properties are quite different. 

Which of the following properties are typical characteristics of a covalent-network solid, a metallic solid, or both (a) ductility, (b) hardness, (c) high melting point ... 

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