F.3chem 急!!!!

In diamond and silicon dioxide, there are strong covalent bonds, but no van der Waals forces. In graphite, there are strong covalent bonds and van der Waals forces.

In diamond, each C atom is covalently bonded with 4 adjacent C atoms, and thus the C atoms are held together by a network of strong covalent bonds.

圖片參考：http://ibchem.com/IB/ibfiles/bonding/bon_img/diamond.gif


In silicon dioxide (SiO2), each Si atom is joined tetrahedrally with 4 O atoms with strong covalent bonds and each O atom is joined with 2 Si atoms, and thus the Si and O atoms are held together by a network of strong covalent bonds.

圖片參考：http://volga.eng.yale.edu/sohrab/grouppage/pics/SiO2bulksupercell_thumb.jpg


In graphite, each C atom is joined triangularly with 3 adjacent atoms. Therefore, C atoms are joined together by strong covalent bonds to form layers, and the layers of atoms are held together by van der Waals’ forces.

圖片參考：http://www.geocities.com/CapeCanaveral/Launchpad/5226/graphite.gif