1. 1
   A drilling company fits diamond tips to its rock-drilling equipment because diamond is the hardest known natural material. The engineer testing the drill bits also checks whether the diamond tips conduct electricity, in case this could cause a safety issue near electrical cabling underground.

   (a)

   Which statement describes the bonding arrangement in diamond that gives it this extreme hardness?

   [1 mark]

   • AEach carbon atom forms four strong covalent bonds with four other carbon atoms, forming a rigid giant covalent structure
   • BEach carbon atom forms three covalent bonds and one weak intermolecular bond
   • CCarbon atoms in diamond are held together by strong electrostatic forces between ions
   • DCarbon atoms in diamond are arranged in layers with weak forces between them

   (b)

   The engineer finds that the diamond tips do not conduct electricity at all. Which statement explains this observation?

   [1 mark]

   • ADiamond is a metal, so it should conduct electricity, but the drilling process removes this property
   • BEvery one of carbon's four outer electrons is used in a covalent bond, so there are no delocalised electrons free to move and carry charge
   • CDiamond contains ions that are held too tightly to move
   • DDiamond conducts electricity only when cut into a particular shape

   (c)

   Explain, in terms of structure and bonding, why diamond is extremely hard and does not conduct electricity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A jeweller sets a diamond into a ring, choosing it partly because it will not scratch or wear down over decades of daily use. A customer asks the jeweller whether the diamond ring could conduct an electric shock if it touched a live wire.

   (a)

   Which statement best explains why diamond resists scratching so well?

   [1 mark]

   • ADiamond has a layered structure that resists scratching because the layers cannot separate
   • BDiamond atoms are packed closely together but are only weakly attracted to each other
   • CEvery carbon atom is held rigidly in place by four strong covalent bonds, so a very large force is needed to disturb the structure
   • DDiamond is scratch-resistant because it contains delocalised electrons that repel other materials

   (b)

   The jeweller reassures the customer that the diamond itself would not conduct an electric shock. Which statement correctly explains why?

   [1 mark]

   • ADiamond ions are too large to move through the structure
   • BDiamond is coated with a special layer that blocks electricity
   • CDiamond only conducts electricity in sunlight
   • DAll four outer electrons of each carbon atom in diamond are held in fixed covalent bonds, leaving none free to move and carry current

   (c)

   Explain why a diamond ring would be a safe choice of jewellery in terms of both its resistance to wear and its lack of electrical conductivity, referring to its structure and bonding.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A geologist compares a sample of diamond with a sample of graphite, both forms of the element carbon. She finds that diamond is extremely hard, while graphite is soft and slippery. She also tests both samples for electrical conductivity.

   (a)

   Explain, in terms of the arrangement of carbon atoms, why diamond is so much harder than graphite, even though both are made only of carbon atoms.

   [3 marks]

   (b)

   The geologist tests both samples for electrical conductivity and finds that diamond does not conduct electricity, while graphite does. Explain, in terms of the number of covalent bonds each carbon atom forms, why these two forms of carbon differ so much in electrical conductivity.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An industrial equipment designer is choosing a coating material for the cutting edge of saw blades used to cut through hard stone. She selects a thin layer of synthetic diamond. The blades are used in a workshop close to electrical machinery and cabling.

   (a)

   Describe, in terms of the structure and bonding of diamond, why it is an excellent choice for this application, and explain why diamond does not conduct electricity, which is relevant because the blades are used near electrical machinery.

   [6 marks]

   (b)

   The designer also considers coating the blades with graphite instead, but rejects this idea. Explain, in terms of structure and bonding, why graphite would not be a suitable substitute for diamond as a cutting-edge coating for stone-cutting blades, even though both are forms of carbon, referring to both hardness and electrical safety.

   [6 marks]

   Total for question 4: 12 marks

End of questions