1. 1
   A precision cutting tool manufacturer applies a diamond coating to the tips of industrial drill bits used to cut through extremely hard rock and metal. The engineering team is explaining to new apprentices why diamond is chosen for this purpose based on its atomic structure.

   (a)

   A precision cutting tool manufacturer coats the tips of its drill bits with diamond to cut through extremely hard materials. Diamond is a form of carbon in which each carbon atom forms four covalent bonds to neighbouring carbon atoms. What type of structure does this arrangement produce?

   [1 mark]

   • AA simple molecular structure
   • BA giant covalent structure
   • CA giant ionic lattice
   • DA metallic structure

   (b)

   The engineering team explains that diamond has an extremely high melting point and is the hardest known natural substance. What is the main reason for these properties?

   [1 mark]

   • ADiamond has weak intermolecular forces between separate molecules
   • BDiamond is made of oppositely charged ions attracted to each other
   • CDiamond contains free-moving delocalised electrons that hold the structure together
   • DEvery carbon atom is joined to four others by strong covalent bonds extending throughout the whole structure

   (c)

   Explain, in terms of its structure and bonding, why diamond is extremely hard and has a very high melting point, and state whether diamond conducts electricity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A pencil manufacturer uses graphite as the writing core of its pencils, relying on graphite's layered structure to leave marks on paper as thin layers rub off, and its ability to conduct electricity is also exploited in some of the company's specialist conductive pencils.

   (a)

   A pencil manufacturer uses graphite, another form of carbon, as the core material in its pencils because it leaves a mark and can be sharpened easily. In graphite, each carbon atom forms only three covalent bonds, arranged in flat hexagonal layers. What structural feature allows the layers in graphite to slide over each other, leaving marks on paper?

   [1 mark]

   • AThere are no covalent bonds between the layers, only weak forces holding the layers together
   • BEach layer is held to the next by strong ionic bonds
   • CThe layers are fused together by strong covalent bonds
   • DGraphite has no layered structure at all

   (b)

   The manufacturer also produces a small range of conductive graphite pencils used in electronics assembly. Unlike diamond, graphite conducts electricity. What explains this difference?

   [1 mark]

   • AGraphite contains free-moving ions that diamond does not have
   • BGraphite is a metal, unlike diamond
   • CEach carbon atom in graphite forms only three covalent bonds, leaving one electron per atom delocalised and free to move through the layers
   • DGraphite has weaker covalent bonds than diamond, allowing current to flow

   (c)

   Explain why graphite can be used as a lubricant in some industrial machinery, and explain why graphite conducts electricity while diamond does not, even though both are forms of carbon.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A construction company uses sand, which is largely composed of silicon dioxide, as a key raw material in its concrete production. Engineers at the company are documenting why silicon dioxide contributes to the strength and durability of concrete structures.

   (a)

   A construction company uses sand, largely made of silicon dioxide, in concrete production. Silicon dioxide is 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. Explain why silicon dioxide has a very high melting point and is used in concrete, which must withstand high loads and remain stable over long periods.

   [3 marks]

   (b)

   The construction company is comparing silicon dioxide with graphite, which is used elsewhere in the company's products as an additive to reduce friction in machinery joints. Explain the key difference in bonding structure between silicon dioxide and graphite that means silicon dioxide is extremely hard throughout, while graphite's layers can slide over each other, and explain why silicon dioxide, unlike graphite, does not conduct electricity.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An electronics research team is investigating graphene, a single isolated layer of carbon atoms taken from graphite's layered structure, as a candidate material for flexible touchscreens because of its unusual combination of strength, flexibility and electrical conductivity.

   (a)

   An electronics research team is developing next-generation flexible touchscreens and is investigating graphene, a single layer of graphite, as a potential material because of its exceptional strength, flexibility and electrical conductivity. Explain, with reference to its atomic structure and bonding, why graphene has these properties, and compare graphene's structure to that of diamond and graphite to explain why graphene behaves so differently despite all three being forms of carbon.

   [6 marks]

   (b)

   The research team is also evaluating fullerenes, including carbon nanotubes, as an alternative to graphene for reinforcing composite materials in the touchscreen's protective casing. Describe the structure of fullerenes, including carbon nanotubes, and evaluate why their structure makes them suitable for use as a reinforcing material in composites, comparing this use to a typical application of graphene.

   [6 marks]

   Total for question 4: 12 marks

End of questions