Covalent network bonds/bonding structure

For each type of bonding structure (molecular, ionic, metallic, and covalent network), describe the structural units in the solid phase and explain how they are bonded. How are the four types similar and different ... 

Until recently, the element carbon was thought to occur in only two allotropic forms diamond and graphite. Both allotropes are covalent network solids, whose structures we discussed in detail in Section 11.8. In diamond, each carbon atom is tetrahedrally (sp ) bonded to four other carbon atoms (see Figure 11.27 in Section 11.6). The result is a three-dimensional network structure in which every carbon atom is covalently bonded to four other carbon atoms. To move one plane of atoms in the diamond crystal relative to another requires the breaking of many strong carbon—carbon bonds. Because of this, diamond is the hardest material known, and its principal industrial use is as an abrasive (grinding material). 

Quartz (Si02) has a network covalent bond structure... 

Note 2 If the permanent paths through the structure of a network are all formed by covalent bonds, the term covalent network may be used. 

The bonding features in the charge density are pronounced in crystals with extended covalent networks. The availability of perfect silicon crystals has allowed the measurement of uncommonly accurate structure factors, of millielectron accuracy. The data have served as a test of experimental formalisms for charge density analysis, and at the same time have provided a stringent criterion for quantum-mechanical methods. 

Carbon exists in more than 40 known structural forms, or allotropes, several of which are crystalline but most of which are amorphous. Graphite, the most common allotrope of carbon and the most stable under normal conditions, is a crystalline covalent network solid that consists of two-dimensional sheets of fused six-membered rings (Figure 10.26a). Each carbon atom is sp2-hybridized and is connected to three other carbons. The diamond form of elemental carbon is a covalent network solid in which each carbon atom is sp3-hybridized and is bonded with tetrahedral geometry to four other carbons (Figure 10.26b). 

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 ... 

Organic substances such as methane, naphthalene, and sucrose, and inorganic substances such as iodine, sulfur trioxide, carbon dioxide, and ice are molecular solids. Salts such as sodium chloride, potassium nitrate, and magnesium sulfate have ionic bonding structures. All metal elements, such as copper, silver, and iron, have metallic bonds. Examples of covalent network solids are diamond, graphite, and silicon dioxide. 

To understand the subtlety and electronic structure of the complex covalent network of /9-R105 boron, it is useful to view the contents of the unit cell [Fig. 13.4.11(b)] as assembled from Bi2fl (at the center of a B84 cluster) and B57 (lying on a C3 axis) fragments connected by 2c-2e bonds. 

The particles in a solid are held together with sufficient force to maintain a rigid structure. In some cases, these forces consist of intermolecular forces, while in others, chemical bonds. Solids are typically classified according to the types of forces that hold the particles together. When classified this way, the four types of solid are molecular, ionic, covalent network, and metallic. 

Answer The correct answer is Si02(quart —> Si02(g). Si02(< t/ariz) is a covalent network solid. Therefore, in its crystalline form, the rigid solid structure is maintained by covalent bonds. The other examples only involve the breaking of various intermolecular forces. 

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 ... 

Covalent solids (or network solids ) can be considered giant molecules that consist of covalently bonded atoms in an extended, rigid crystalline network. Diamond (one crystalline form of carbon) and quartz are examples of covalent solids (Figure 13-32). Because of their rigid, strongly bonded structures, mst covalent solids are very hard and melt at high temperatures. Because electrons are localized in covalent bonds, they are not freely... 

The primary structure of macromolecules is defined as the sequential order of monomers connected via covalent chemical bonds. This structural level includes features such as chain length, order of monomer attachment in homopolymers (head-to-head, head-to-tail placement), order of monomer attachment in various copolymers (block copolymers, statistical and graft copolymers, chemical composition of co-monomers), stereoregularity, isomers, and molecular topology in different branched macromolecules and molecular networks. Structure at this primary level can be manipulated by polymer synthesis [4]. With AFM it is possible to visualize, under certain conditions, single macromolecules (Fig. 3.2) and it is even possible to manipulate these (i.e. push with AFM tips). Characteristics of chain-internal... 

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