Types of Matter Structure and Bonding

There are several ways to categorize materials. One way is to group them according to their use or function. Thus structural materials, such as metals, plastics, concrete, and building ceramics, used in construction are chosen for their mechanical 

Electronic conductors Semiconductors Ionic conductors Mixed conductors Ferrimagnetics Thermal conductors Thermal insulators Chromophores Translucent materials Nonlinear optics Photovoltaics Transparent conductors Active materials Inert materials Biocompatibles 

sensors Fuel cell electrolytes Fuel cell electrodes Information recording Heat exchangers Refractories Pigments, ion lasers Fiber optics Switches Solar cells Displays Catalysts 

Materials can also be grouped according to the way their atoms are bound. Molecules have strong intramolecular and weak intermolecular bonds while atomic solids have strong interatomic bonds in extended lattices. A materials engineer is interested in the crystal structure of a material because the (intrinsic) properties depend on it. The structures of some molecules and crystal lattices are shown in several figures further on in this chapter following a brief review of chemical bonds. 

The covalent bond has localized electrons, and has little or no net charge transfer from one atom to the other. Silicon and diamond are prototypes of solids having covalent bonds, and the bonds in hydrogen and nitrogen molecules are also purely covalent. These bonds are oriented in space with respect to each other. Four-coordination (four nearest-neighbor atoms) often indicates covalency. Examples of covalent bonds in binary compounds are found in the solid silicon carbide (SiC) and nitrogen chloride molecules (NCI3). 

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