Rocks and minerals
Many other compounds have giant covalent structures. They generally have the similar properties of hardness, high melting and boiling points, and low electrical conductivity.
A good example is diamond. This is made of carbon atoms, with each joined to four others by strong covalent bonds.
Diamond is the hardest naturally occurring substance. It is used as a gemstone, but also on the cutting edges of drills and saws.
Graphite is another giant covalent structure made of carbon atoms. In graphite, each carbon atom is joined to three others, forming layers:
The bonds between the layers are much weaker than covalent bonds. This enables the layers to slide across each other, making graphite soft. Graphite can also conduct electricity, between the layers of carbon atoms.
Graphite is used as pencil ‘lead’. As the pencil moves across the paper, layers of graphite rub off. Graphite is also used as a lubricant, and as an electrode in electrolysis - for example, in the manufacture of aluminium.
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