Solids covalent network

Solids with different structures, (a) Diamond, a network covalent solid, (b) Potassium dichromate. K2 2O7, an ionic solid, (c) Manganese, a metallic solid. 

SiC(s) is a network covalent solid. It contains covalent bonds between its atoms. It doesn t have any freely moving electrons or ions and so SiC doesn t conduct electricity... 

Network covalent solids have covalent bonds joining the atoms together in the crystal lattice, which is quite large. Graphite, diamond, and silicon dioxide (Si02) are examples of network solids. 

Figure 9.1 4 Covalent bonds of network covalent solids. A, In quartz (Si02), eaoh Si atom is bonded covalently to four O atoms and each O atom is bonded to two Si atoms in a pattern that extends throughout the sample. Because no separate SD2 molecules are present, the melting point of quartz is very high, and it is very hard. B, In diamond, each C atom is covalently bonded to four other C atoms throughout the crystal. Diamond is the hardest natural substance known and has an extremely high melting point.

By far the most important network covalent solids are the silicates. They utilize a variety of bonding patterns, but nearly all consist of extended arrays of covalently bonded silicon and oxygen atoms. Quartz (Si02) is a common example. We ll discuss silicates, which form the structure of clays, rocks, and many minerals, when we consider the chemistry of silicon in Chapter 14. 

Physical properties reflect the change from individual molecules (N, P) to network covalent solid (As, Sb) to metal (Bi). Thus, melting points increase and then decrease. Large atomic size and low atomic mass result in low density. Because mass increases more than size down the group, the density of the elements as solids increases. The dramatic increase from P to As is due to the intervening transition elements. 

How do the physical properties of a network covalent solid and a molecular covalent solid differ Why ... 

The crystal structure of graphene illustrates two important characteristics of crystals. First, we see that no atoms lie on the lattice points. While most of the structures we discuss in this chapter do have atoms on the lattice points, there are many examples, like graphene, where this is not the case. Thus, to build up a structure you must know the location and orientation of the atoms in the motif with respect to the lattice points. Second, we see that bonds can be formed between atoms in neighboring unit cells. This happens in many crystals, particularly metallic, ionic, and network-covalent solids. 

The diagonal elements boron and silicon also have similar properties. The chlorides of both elements form network covalent solids that act as Lewis bases toward water, reacting according to Equations (5.11) and (5.12) ... 

With few exceptions, the metal oxides are ionic solids and react with water to form aqueous ions, the nonmetal oxides are network covalent solids that react with water to make covalent compounds, and the amphoteric oxides of the metalloids form oligomeric polar-covalent solids. Similar relationships hold for the hydrides and fluorides of each element, with the metal forming an ionic solid and the non-metal forming a network covalent solid, although the actual demarcation line varies somewhat depending on the anion. 

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