Covalent network solids table

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. 

Solution (a) Si3N4 is a ceramic material. We can think of it as analogous to silicon carbide, a very hard covalent-network solid (Section 11.8). It should have high -melting and boiling points and be very hard (Table 12.4). Because Si and N are both nonmetals, the bonding between them should be polar covalent. 

For ionic solids and covalent network solids to melt, chemical bonds must be broken. For that reason, the melting points of these types of solids are relatively high. The melting point of the ionic solid sodium chloride is 801°C that of magnesium oxide is 2800°C. Melting points of covalent network solids are generally quite high. Quartz, for example, melts at 1610°C diamond, at 3550°C. See Table 11.1. ... 

In sharp contrast to molecular solids, network solids have very high melting points. Compare the behavior of phosphorus and silicon, third-row neighbors in the periodic table. As listed in Table 11-2. phosphorus melts at 317 K, but silicon melts at 1683 K. Phosphorus is a molecular solid that contains individual P4 molecules, but silicon is a network solid in which covalent bonds among Si atoms connect all the atoms. The vast array of covalent bonds In a network solid makes the entire stmcture behave as one giant molecule. ... 

Indicate the type of solid (molecular, metallic, ionic, or covalent-network) for each compound (a) CaC03, (b) Pt, (c) Zr02 (melting point, 2677 °C), (d) table sugar (C12H22O11),... 

Ceramics are inorganic, nonmetallic, solid materials. They can be crystalline or noncr5 talline. Noncrystalline ceramics include glass and a few other materials with amorphous structures. Ceramics can possess a covalent-network structure, ionic bonding, or some combination of the two. (Section 11.8, Table 11.6) They are normally hard and brittle and are stable to very high temperatures. Ceramic materials include familiar objects such as pottery, china, cement, roof tiles, refractory bricks used in furnaces, and the insulators in spark plugs. 

So far we have considered solids in which atoms occupy the lattice positions. In some of these substances (network solids), the solid can be considered to be one giant molecule. In addition, there are many types of solids that contain discrete molecular units at each lattice position. A conunon example is ice, where the lattice positions are occupied by water molecules [see Fig. 10.12(c)], Other examples are dry ice (solid carbon dioxide), some forms of sulfur that contain Sg molecules [Fig. 10.32(a)], and certain forms of phosphorus that contain P4 molecules [Fig. 10.32(b)]. These substances are characterized by strong covalent bonding within the molecules but relatively weak forces between the molecules. For example, it takes only 6 kJ of energy to melt 1 mole of solid water (ice) because only intermolecular (H2O—H2O) interactions must be overcome. However, 470 kJ of energy is required to break 1 mole of covalent O—H bonds. The differences between the covalent bonds within the molecules and the forces between the molecules are apparent from the comparison of the interatomic and intermolecular distances in solids shown in Table 10.6. 

Metals conduct electricity extremely well. Many solids, however, conduct electricity somewhat, but nowhere near as well as metals, which is why such materials are called semiconductors. Two examples of semiconductors are silicon and germanium, which he immediately below carbon in the periodic table. Like carbon, each of these elements has four valence electrons, just the right number to satisfy the octet rule by forming single covalent bonds with four neighbors. Hence, silicon and germanium, as well as the gray form of tin, crystalhze with the same infinite network of covalent bonds as diamond. 

As a consequence of strong bonding, all network covalent solids have extremely high melting and boiling points, but their conductivity and hardness vary. Two examples with the same composition but strikingly different properties are the two common crystalline forms of elemental carbon, graphite and diamond (Table 12.6) ... 

The diagonal relationship between beryllium and aluminum, discussed previously in Chapter 21, is evident in Table 22.1. Both beryllium (in group 2) and aluminum (in group 13) form network covalent solids with fluorine. 

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