Network atomic solids carbon

The hardest network atomic solid—in fact, the hardest (currently) known material on the planet—is a type of carbon that forms diamonds. The covalently bonded arrangement of carbon atoms within diamonds forms naturally at intense temperatures and pressures inside the Earth. 

Many atomic solids contain strong directional covalent bonds. We will call these substances network solids. In contrast to metals, these materials are typically brittle and do not efficiently conduct heat or electricity. To illustrate network solids, in this section we will discuss two very important elements, carbon and silicon, and some of their compounds. 

Diamond is a network of carbon atoms, each carbon entity bonded to the next through a covalent bond in a tetrahedron arrangement, as shown in figure 1.12.3. Diamond s sibling, solid graphite, is also made of pure carbon, but in graphite the carbons are bonded in sheets that can slide over... 

Elemental silicon does not occur free in nature rather it is found as silicon dioxide (sometimes called silica Si02) and in an enormous variety of silicate minerals. In contrast to the oxides of carbon, which are volatile molecular species held together by London forces in the solid state, Si02 forms very stable, nonvolatile, three-dimensional network crystals. One of the three crystal modifications of SiOj has a lattice that may be considered to be derived from the diamond lattice, with silicon atoms replacing carbon atoms and an oxygen atom midway between each pair of them. 

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 common 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 Ss molecules [Fig. 10.34(a)], and certain forms of phosphorus that contain P4 molecules [Fig. 10.34(b)]. These substances are characterized by strong... 

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