4. Electron Sharing and      Covalent Bonds  
     Diamond and Graphite

In the simple, single-bonded hydrocarbons discussed previously, some of the four tetrahedrally arranged atoms around each carbon are hydrogen atoms and some are carbon atoms. One can imagine a three-dimensional tetrahedral framework in which all of the atoms are carbons and no hydrogens are present. The result would be the tetrahedral structure shown on the right, with each carbon atom connected to four other carbon atoms by single electron-pair bonds. This is the structure of diamond. Diamond is very hard and rigid because any breaking off or deforming of part of the diamond structure requires a breaking or stretching of strong electron-pair bonds. In contrast, paraffin wax has linear chains of carbon atoms, but only weak van der Waals forces to hold the molecules together. If subjected to external stress, the molecules slip past one another to new positions. Wax is soft because the van der Waals forces are weak; diamond is hard because the electronpair bonds in its three-dimensional network are strong.

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