In a giant covalent structure, a huge number of atoms are joined by strong covalent bonds in a network. There are no separate small molecules. A lot of energy is needed to break the many strong bonds, so these substances have very high melting points.
Diamond is made only of carbon. Each carbon bonds to four other carbon atoms in a rigid 3D network. The diagram shows a small local section; the bonds continue through the diamond.
| Property | Explanation | Useful for… |
|---|---|---|
| Very hard | Strong bonds hold atoms in a rigid 3D network. | Cutting and drilling |
| Very high melting point | Many strong covalent bonds need much energy to break. | Use where heat resistance is needed |
| Does not conduct electricity | All four outer electrons are used in bonds; no mobile charged particles. | Electrical insulation |
Silicon dioxide, SiO₂, also called silica, is another giant covalent substance. It contains silicon and oxygen atoms joined throughout a network, rather than separate SiO₂ molecules. It has a high melting point and does not conduct electricity. You need to recognise this structure; detailed silicon dioxide dot-and-cross diagrams are not required.
Diamond: carbon makes four bonds in a rigid 3D network. Diamond and silica have high melting points and no mobile charge carriers.
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