Define — 2 marks
A materials scientist is investigating different substances used in smartphone screens. She compares diamond (used in protective coatings), graphite (used in conductive layers), and silicon dioxide (used in glass). Each material has very different properties despite being made of carbon or oxygen and silicon atoms.
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Define what is meant by the term 'giant covalent structure'.
[2 marks]
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- A structure where atoms are bonded together by covalent bonds in a continuous/repeating 3D network (1 mark)
- Extending throughout the whole substance / with no individual molecules / atoms held in fixed positions (1 mark)
Describe — 4 marks
A materials scientist is investigating two substances for use in aircraft components. Substance A is diamond (a form of carbon), and Substance B is silicon dioxide (SiO₂). Both materials are extremely hard and have high melting points, making them suitable for high-temperature applications. The scientist needs to understand the relationship between their atomic structures and their properties.
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(a) Describe the structure of diamond in terms of its atoms and bonding.
[2 marks]
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(b) Describe the structure of silicon dioxide and explain why it has a very high melting point.
[2 marks]
Show mark scheme
- (a) Diamond consists of carbon atoms arranged in a giant covalent/network structure (1 mark)
- (a) Each carbon atom is bonded to four other carbon atoms by strong covalent bonds in a tetrahedral arrangement (1 mark)
- (b) Silicon dioxide is a giant covalent/network structure made of silicon and oxygen atoms linked by covalent bonds throughout (1 mark)
- (b) It has a very high melting point because there are many strong covalent bonds throughout the entire structure that must be broken to melt it (1 mark)
State — 5 marks
A materials scientist is investigating three substances for use in aerospace manufacturing: diamond, silicon dioxide (quartz), and sodium chloride. Each material has different structural properties that make them suitable for different applications. The scientist needs to understand how the arrangement of particles in each substance relates to its physical properties.
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(a) State the type of bonding present in diamond.
[1 mark]
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(b) State two reasons why diamond is harder than sodium chloride, by referring to their structures.
[2 marks]
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(c) State the structure type of silicon dioxide and explain why it has a higher melting point than sodium chloride despite both being giant structures.
[2 marks]
Show mark scheme
- (a) Covalent bonding (accept: strong covalent bonds)
- (b) Diamond has a continuous network of strong covalent bonds throughout the entire structure, whereas sodium chloride has ionic bonds between discrete ions
- (b) Diamond has no planes of weakness / cleavage planes, while sodium chloride has cleavage planes where ionic layers can separate
- (c) Silicon dioxide has a giant covalent structure (accept: network covalent structure)
- (c) Silicon dioxide has strong covalent bonds throughout the structure that must be broken on melting, whereas sodium chloride only requires ionic bonds to be overcome, which are weaker than the covalent bonds in SiO₂
Describe — 3 marks
A student is investigating different materials used in kitchen utensils. They examine a wooden spoon, an aluminium foil container, and a glass bowl. Each material has different properties that make it suitable for different uses.
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(a) Describe the structure of a metal such as aluminium.
[2 marks]
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(b) Explain how the structure of aluminium results in it being a good conductor of electricity.
[1 mark]
Show mark scheme
- (a) Metal atoms/cations arranged in a regular/lattice structure (1 mark)
- (a) Delocalised electrons/sea of electrons that are free to move throughout the structure (1 mark)
- (b) The delocalised/free electrons can move through the structure/carry charge/conduct electricity (1 mark)
Calculate — 2 marks
A student is investigating the properties of ionic compounds in a school laboratory. They are calculating the relative formula mass of magnesium oxide (MgO) to help them prepare a solution of known concentration. The relative atomic masses are: Mg = 24, O = 16.
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(a) Calculate the relative formula mass of magnesium oxide (MgO).
[1 mark]
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(b) The student needs to prepare 40 g of magnesium oxide. Calculate the mass of magnesium needed to make this amount of magnesium oxide.
[1 mark]
Show mark scheme
- (a) 40 (1)
- (b) 24 g (1) OR 40 × 24/40
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