Giant covalent structures of carbonEdexcel International A Level Chemistry: Subtopic test

1. 1
   A drilling company fits diamond-tipped bits to its rock drills. The same company also supplies graphite for use as a dry lubricant and as electrodes.

   (a)

   Which statement explains why diamond is very hard?

   [1 mark]

   • AEach carbon atom is bonded to four others by strong covalent bonds in a rigid three-dimensional lattice.
   • BLayers of atoms held together by weak forces slide over each other.
   • CDelocalised electrons hold the lattice together.
   • DStrong ionic attractions act between carbon ions.

   (b)

   Why can graphite be used as an electrode?

   [1 mark]

   • AIt contains free ions that carry charge.
   • BAll four outer electrons on each carbon atom are held in covalent bonds.
   • COne outer electron on each carbon atom is delocalised and free to move through the structure.
   • DIts layers can slide, so charge flows between them.

   (c)

   Explain why graphite is soft and can be used as a lubricant.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Graphene is a single layer of graphite, one atom thick, in which carbon atoms are arranged in a hexagonal network. It is being developed for transparent, flexible touch screens and for strong, lightweight composite materials.

   (a)

   How many other carbon atoms is each carbon atom in graphene bonded to?

   [1 mark]

   • A2
   • B3
   • C4
   • D6

   (b)

   Which statement explains why graphene is suitable as the conducting layer of a flexible touch screen?

   [1 mark]

   • AIt is an electrical insulator and very hard.
   • BIt has weak forces between the atoms in the sheet, so it is easily torn.
   • CIt conducts electricity but is opaque.
   • DIt conducts electricity and, being one atom thick, is transparent.

   (c)

   Explain why graphene conducts electricity.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Diamond and graphite are both forms of pure carbon and both have very high melting points. Diamond has a density of 3.51 g cm⁻³ and does not conduct electricity. Graphite has a density of 2.27 g cm⁻³ and does conduct electricity. In graphite the distance between neighbouring layers is 0.335 nm, which is more than twice the carbon–carbon bond length within a layer, 0.142 nm.

   (a)

   Explain, in terms of structure and bonding, why diamond has a very high melting point and does not conduct electricity.

   [3 marks]

   (b)

   Explain why graphite has a lower density than diamond, but still has a very high melting point.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A materials company needs a form of carbon for two jobs: the transparent conducting layer of a flexible touch screen, and the tip of a rock drill. It is considering diamond, graphite and graphene.

   (a)

   Compare the structure and bonding of diamond and graphite, and explain the differences in their hardness and electrical conductivity.

   [6 marks]

   (b)

   Evaluate the suitability of diamond, graphite and graphene for each of the two jobs, and conclude which form of carbon should be used for each.

   [6 marks]

   Total for question 4: 12 marks

End of questions