Giant Covalent Structures
Get to grips with Giant Covalent Structures for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Giant covalent structures such as diamond and silicon dioxide have very high melting points because many strong covalent bonds must be broken.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Giant covalent structures contain very many atoms joined by strong covalent bonds in a continuous network. There are no separate molecules.
Because the whole structure is held together by strong covalent bonds, a very large amount of energy is needed to break them. Giant covalent substances therefore have very high melting and boiling points and are all solids at room temperature.
Most do not conduct electricity, because there are no charged particles free to move — graphite is the important exception. Diamond, silicon dioxide and graphite are the required examples, and each is examined through its structure explaining its properties.
Revision notes
The structure
Very many atoms are joined by strong covalent bonds in a continuous network.
There are no separate molecules and no intermolecular forces to consider — the bonding extends throughout the whole structure.
High melting points
Melting or boiling requires breaking many strong covalent bonds.
This needs a very large amount of energy, so giant covalent substances have very high melting and boiling points and are solids at room temperature.
Conductivity
Most giant covalent substances do not conduct electricity, because all the outer electrons are used in bonding and there are no free charged particles.
Graphite is the exception: each carbon atom forms only three bonds, leaving one delocalised electron per atom free to move and carry charge.
Key points
- Giant covalent structures contain many atoms bonded throughout.
- There are no separate molecules.
- Strong covalent bonds must be broken to melt them.
- They have very high melting and boiling points.
- Most do not conduct electricity.
- Graphite is the exception because of delocalised electrons.
Worked examples
Example 1
Explain why giant covalent structures have very high melting points. [2 marks]
Model answer
The atoms are held together by strong covalent bonds throughout the whole structure (1 mark), so a very large amount of energy is needed to break the many bonds (1 mark).
Example 2
Explain why diamond does not conduct electricity. [2 marks]
Model answer
Each carbon atom forms four covalent bonds, using all of its outer electrons (1 mark), so there are no delocalised electrons or free ions to carry charge (1 mark).
Example 3
Explain why silicon dioxide has a high melting point. [2 marks]
Model answer
It has a giant covalent structure in which every atom is joined to others by strong covalent bonds (1 mark), so a great deal of energy is required to break them all (1 mark).
Common mistakes
Saying intermolecular forces are overcome on melting.
There are no separate molecules — covalent bonds themselves must be broken.
Saying all giant covalent substances conduct.
Only graphite does, because of its delocalised electrons.
Calling diamond a molecule.
It is a giant structure, not a simple molecular substance.
Forgetting to say the bonds are strong.
The strength of the bonds is what explains the high melting point.
Exam tips
- Say covalent bonds must be broken, not intermolecular forces.
- Explain non-conductivity through all electrons being used in bonding.
- Learn diamond, silicon dioxide and graphite as your examples.
- Emphasise that bonding extends throughout the structure.
Key terms
- Giant covalent
- A structure of many atoms bonded covalently throughout.
- Macromolecule
- Another term for a giant covalent structure.
- Silicon dioxide
- A giant covalent substance, also called silica.
- Delocalised electron
- A free-moving electron, present in graphite only.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.