Covalent network

Fig. 10.6 Drawings of students about their ideas of hard and soft polymer materials. Left, a student (7th grade) argues with the closeness of the arrangement of particles. On the right a student from 12th grade. The difference is caused in the closeness of the covalent network...

The unique properties of SDIBS are due to the branched structure of the DIB core, and consequently the double-network stmcture in which a covalent network is embedded into a self-assembling thermolabile network, as shown in Figure 7.9. 

The structure of a-C H films may be thus pictured as sp--carbon atoms in condensed aromatic clusters, dispersed in an sp- -rich matrix, which confers to the network its characteristic rigidity. This situation can also be regarded as a random covalent network in which the sp" clusters of a defined size take part in the structure as an individual composed atom with its corresponding coordination number [17]. Such kinds of models have been successfully used to describe the dependence of a-C H film mechanical properties on composition, hybridization, and sp" clustering [23]. 

Solids can be classified into four categories ionic, metallic, covalent network, and molecular. For each of the four categories, identify the basic structural unit describe the nature of the force both within the unit and between units cite the basic properties of each type of solid give two examples of each type of solid and describe a laboratory means of identifying each type of solid. 

Characteristic Ionic Metallic Covalent Network Molecular... 

Si02(s) forms an ordered, structured covalent network. 

D—Both graphite and diamond are covalent-network solids. 

In covalent network solids, covalent bonds join atoms together in the crystal lattice, which is quite large. Graphite, diamond, and silicon dioxide (Si02) are examples of network solids. The crystal is one giant molecule. 

A—This answer describes a covalent network solid. 

B—Diamond is a covalent network solid with a large number of strong covalent bonds between the carbon atoms. 

To search for the inverted region, experiments were designed so that the donor-acceptor distances were kept fixed by attaching them to a covalent network of rigid spacers, frozen media, electrostatic com-plexation, and protein frameworks. In all of these cases, the... 

Covalent Network atoms covalent bonds very high low hard crystals that are insoluble in most liquids formed usually from elements belonging to Group 14 (IV A) graphite, diamond, Si02... 

Tropocollagen molecules are firmly linked together, particularly at their ends, by covalent networks of altered lysine side chains. The number of these links increases with age. Type IV collagens form networks with a defined mesh size. The size-selective filtering effect of the basal membranes in the renal glomeruli is based on this type of structure (see p. 322). 

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. 

Much of the interest in the polysilanes, polygermanes, and polystannanes involves their sigma delocalization and their sigma-pi delocalization when coupled with arenes or acetylenes. This is not unexpected since silicon exists as a covalent network similar to diamond. In exhibiting electrical conductivity, germanium and tin show more typical metallic bonding. Some polystannanes have been referred to as molecular metals. ... 

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. 

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