1. 1
   A materials engineer is comparing electrical cables made from different metals. She tests a length of copper wire, noting that it conducts electricity well and can be bent around corners without snapping.

   (a)

   Copper is a solid at room temperature. Which particles are responsible for carrying the electric current through the solid copper wire?

   [1 mark]

   • ADelocalised electrons that are free to move through the metallic lattice
   • BProtons held fixed inside the nucleus of each copper atom
   • CNeutrons moving between the positive copper ions
   • DCopper ions that break free of the lattice and flow through the wire

   (b)

   The engineer also notes that the copper wire can be bent around corners without snapping. Which explanation, in terms of structure and bonding, accounts for this property?

   [1 mark]

   • ACovalent bonds between copper atoms break and reform as the wire is bent
   • BLayers of positive copper ions can slide over one another while the sea of delocalised electrons continues to hold the structure together
   • CThe copper ions form new ionic bonds with each other as the wire changes shape
   • DThe copper atoms sublime and re-solidify in the new shape

   (c)

   Explain, in terms of structure and bonding, why solid copper conducts electricity.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A chef notices that an aluminium saucepan heats up quickly and evenly when placed on a hob, and that its handle also becomes uncomfortably hot unless it is covered.

   (a)

   Which feature of aluminium's structure explains why it transfers heat energy so efficiently?

   [1 mark]

   • AAluminium has a simple molecular structure with small individual molecules
   • BAluminium atoms are held together by weak intermolecular forces that vibrate rapidly
   • CThe delocalised electrons move throughout the lattice, transferring thermal energy quickly between ions
   • DAluminium ions are only loosely packed, leaving large gaps for heat to pass through

   (b)

   Which statement correctly describes the arrangement of particles in solid aluminium?

   [1 mark]

   • AAluminium atoms joined in small covalent molecules of fixed size
   • BIndividual aluminium atoms held apart by weak forces with no shared electrons
   • CNegative aluminium ions and positive aluminium ions held together in a lattice
   • DA giant regular lattice of positive aluminium ions surrounded by a sea of delocalised electrons

   (c)

   Using the particle model of metallic bonding, explain why the aluminium pan conducts heat well.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A blacksmith heats an iron bar until it glows red-hot, then hammers it repeatedly on an anvil to bend it into the curved shape of a horseshoe.

   (a)

   A blacksmith heats an iron bar until it glows and then hammers it into the curved shape of a horseshoe. Explain, in terms of structure and bonding, why the iron bar can be hammered into a new shape without shattering.

   [3 marks]

   (b)

   The blacksmith also notices that a very high temperature is needed before the iron bar starts to melt. Explain, in terms of metallic bonding, why iron has such a high melting point.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   An engineer is choosing a metal to build a support strut for a bridge. The strut must be bent into curved sections during construction, must not shatter suddenly if struck, and the engineer would also like the material to be recycled easily by melting it down in future.

   (a)

   Using ideas about metallic bonding, explain why metals are typically malleable and describe how the structure of a metal allows it to be shaped without breaking.

   [6 marks]

   (b)

   The engineer also wants the chosen metal to conduct electricity (for lightning protection) and to withstand very high temperatures without melting. Using ideas about metallic bonding, explain why metals conduct electricity and heat well, and why metals generally have high melting points.

   [6 marks]

   Total for question 4: 12 marks

End of questions