AQA GCSE Chemistry (8462), Higher tier · Bonding, structure and the properties of matter › Bonding, structure and properties
Practise Giant covalent structures. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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Substance X has a giant covalent structure. Predict the state of X at room temperature.
solid
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy4 marks
Some substances have giant covalent structures.
(a) Which substance has a giant covalent structure? Tick (✓) one box.[1]
Silicon dioxide
Water
Sodium chloride
Oxygen
(b) Explain why substances with giant covalent structures have very high melting points.[2]
(c) Substance X has a giant covalent structure. Predict the state of X at room temperature.[1]
Show the answer and mark scheme
(a)Answer: Silicon dioxide
(b)Answer: All the atoms are linked by many strong covalent bonds, and a lot of energy is needed to break them.
(many) strong covalent bonds
a lot of energy is needed to break / overcome the bonds
(c)Answer: solid
solid
Question 2Medium6 marks
In silicon dioxide, each silicon atom is covalently bonded to four oxygen atoms. Each oxygen atom is covalently bonded to two silicon atoms.
(a) Explain why the formula of silicon dioxide is SiO2.[2]
(b) Explain why silicon dioxide has a high melting point.[3]
(c) Silicon dioxide does not conduct electricity. Suggest why.[1]
Show the answer and mark scheme
(a)Answer: Each oxygen atom is shared between two silicon atoms, so each silicon atom has 4 × ½ = 2 oxygen atoms.
each oxygen atom is shared between two silicon atoms
so there are 4 × ½ = 2 oxygen atoms for every silicon atom
(b)Answer: It is a giant covalent structure with many strong covalent bonds, which need a lot of energy to break.
giant covalent structure
many strong covalent bonds
a lot of energy is needed to break the bonds
(c)Answer: It has no delocalised electrons or ions that are free to move.
no delocalised electrons / no ions / no charged particles free to move
Question 3Hard6 marks
Silicon carbide, SiC, is used on cutting discs and grinding wheels. In silicon carbide, each silicon atom is bonded to four carbon atoms and each carbon atom is bonded to four silicon atoms, in a structure similar to diamond.
(a) Suggest two physical properties of silicon carbide.[2]
(b) Explain, in terms of structure and bonding, why silicon carbide is suitable for cutting discs.[3]
(c) Explain why the formula of silicon carbide is SiC and not SiC4.[1]
Show the answer and mark scheme
(a)Answer: Very hard; very high melting point.
very hard
very high melting point
does not conduct electricity
insoluble in water
(b)Answer: It is a giant covalent structure in which each atom is joined to four others by strong covalent bonds in a rigid 3D network, so it is very hard.
giant covalent structure
each atom is joined to four others by strong covalent bonds (in a rigid 3D network)
so it is very hard / a lot of energy is needed to break the bonds
(c)Answer: Each carbon atom is also bonded to four silicon atoms, so overall there is one carbon atom for every silicon atom.
each carbon atom is also bonded to four silicon atoms, so the ratio of atoms is 1 : 1