AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Some covalently bonded substances have giant covalent structures, such as…
Full specification wording
Covalent bonding: Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide.
A giant covalent structure is a network of many atoms joined by covalent bonds throughout the whole substance, with no separate small molecules.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 6 of 8
- 3 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A giant covalent structure is a network of many atoms joined by covalent bonds throughout the whole substance, with no separate small molecules. Diamond is a giant covalent structure of carbon atoms, each bonded to four others in a tetrahedral network, so it is very hard and has a very high melting point. Silicon dioxide, the main compound in sand, has a giant covalent structure in which each silicon atom is bonded to four oxygen atoms and each oxygen atom is bonded to two silicon atoms. In both substances, melting requires breaking many strong covalent bonds, so the melting points are very high. Unlike simple molecular substances, giant covalent structures do not consist of small groups of atoms.
What earns the marks
- A giant covalent structure is a continuous network of atoms joined by covalent bonds, not separate small molecules.
- In diamond, each carbon atom forms four single covalent bonds to other carbon atoms in a tetrahedral arrangement.
- In silicon dioxide, each silicon atom bonds to four oxygen atoms and each oxygen atom bonds to two silicon atoms.
- Melting a giant covalent substance requires breaking many strong covalent bonds, giving very high melting points.
- Diamond is very hard because its rigid network of strong covalent bonds resists deformation.
Common mistakes and how to put them right
Describing diamond as a simple molecular substance.
Put it right by stating that diamond is a giant covalent network with no separate molecules.
Saying silicon dioxide contains Si₂O₄ molecules.
Put it right by describing a continuous network in which each silicon atom is bonded to four oxygen atoms.
Claiming giant covalent substances melt easily because covalent bonds are weak.
Put it right by explaining that many strong covalent bonds must be broken, so melting points are very high.
Exam tips
- When comparing diamond and silicon dioxide, state the number of bonds formed by each atom in the network.
- Use the phrase giant covalent structure rather than molecule when describing diamond or silicon dioxide.
- Explain high melting point by referring to the many strong covalent bonds that must be broken, not to weak intermolecular forces.
Try the lesson
The start of the Covalent bonding: Some covalently bonded substances have giant covalent structures, such as diamond and silicon dioxide. lesson, made from checked teaching notes for this specification point.
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Which of these substances has a giant covalent structure?
Listen
A giant covalent structure is a network of many atoms joined by covalent bonds throughout the whole substance, with no separate small molecules. Diamond is a giant covalent structure of carbon atoms, each bonded to four others in a tetrahedral network, so it is very hard and has a very high melting point. Silicon dioxide, the main compound in sand, has a giant covalent structure in which each silicon atom is bonded to four oxygen atoms and each oxygen atom is bonded to two silicon atoms. In both substances, melting requires breaking many strong covalent bonds, so the melting points are very high. Unlike simple molecular substances, giant covalent structures do not consist of small groups of atoms. A strong answer earns marks for these points. A giant covalent structure is a continuous network of atoms joined by covalent bonds, not separate small molecules. In diamond, each carbon atom forms four single covalent bonds to other carbon atoms in a tetrahedral arrangement. In silicon dioxide, each silicon atom bonds to four oxygen atoms and each oxygen atom bonds to two silicon atoms. Melting a giant covalent substance requires breaking many strong covalent bonds, giving very high melting points. A common slip: Describing diamond as a simple molecular substance. Instead, stating that diamond is a giant covalent network with no separate molecules. Exam tip: When comparing diamond and silicon dioxide, state the number of bonds formed by each atom in the network.
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Key words
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Giant covalent structures
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Diamond
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Silicon dioxide
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See every definition
- Giant covalent structures
- A continuous network of atoms joined by covalent bonds throughout the whole substance, not separate small molecules.
- Diamond
- A giant covalent structure of carbon atoms, each bonded to four others in a tetrahedral network, so it is very hard and has a very high melting point.
- Silicon dioxide
- The main compound in sand, with a giant covalent structure in which each silicon atom is bonded to four oxygen atoms and each oxygen atom is bonded to two silicon atoms.
Label the diagram
Some boxes have lost their names. Pick the right name for each number.
1Box 1
2Box 2
3Box 3
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