Chemistry
Giant covalent structures Learning objectives: • recognise giant covalent structures from bonding and structure diagrams • explain the properties of giant covalent structures • recognise the differences in different forms of carbon.
KEY WORDS diamond giant covalent structure graphite silicon dioxide
Amethyst, pink quartz and diamond are gems that have giant structures, with bonds in all directions, which make them hard. Quartz is a giant covalent structure made of silicon dioxide. It is the second most abundant mineral in the Earth’s crust. It is the biggest component of sand and can also be coloured with other substances, as in some gems. Diamonds are not abundant and are giant structures made of carbon.
Structure and bonding
Figure 2.32 Pure quartz is silicon dioxide which is colourless. It can be coloured naturally with iron or manganese to make amethyst.
Substances that consist of giant covalent structures are solids. All of the atoms in these structures are linked to other atoms by strong covalent bonds. These bonds must be overcome to melt or boil these substances. These substances with giant structures have very high melting points. Examples of giant covalent structures are: • diamond (a form of carbon) • silicon dioxide (silica or quartz).
KEY INFORMATION Remember you should aim to be able to recognise the different structures of carbon.
Figure 2.33 Diamond and silicon dioxide both have giant covalent structures.
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1
Describe one difference and one similarity in the giant covalent structures of diamond and silicon dioxide.
2
Describe the difference between a molecule like water, H2O, and a giant covalent structure like silicon dioxide.
AQA GCSE Chemistry for Combined Science: Trilogy: Student Book
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