1. 1
   An electrical cabling company manufactures copper wire for domestic house wiring, relying on copper's excellent electrical conductivity. The company's materials scientists are training new engineers on the atomic structure that gives copper its useful electrical properties.

   (a)

   An electrical cabling company manufactures copper wire for use in domestic house wiring, chosen because copper conducts electricity very well. Copper atoms are held together by metallic bonding. What is the correct description of metallic bonding?

   [1 mark]

   • AMolecules held together by weak intermolecular forces
   • BElectrons transferred completely from one atom to another to form oppositely charged ions
   • CPairs of electrons shared between two non-metal atoms
   • DPositive metal ions arranged in a regular pattern with delocalised electrons free to move throughout the structure

   (b)

   The materials scientists explain that copper conducts electricity extremely well because of its structure. What is the main reason metals such as copper conduct electricity?

   [1 mark]

   • AMetal ions are free to move through the structure and carry charge
   • BMetals contain free-moving ions in solution
   • CDelocalised electrons are free to move throughout the structure and carry charge
   • DMetals have weak covalent bonds that break easily to release charge carriers

   (c)

   Explain, in terms of its structure and bonding, why copper is a good conductor of electricity and also a good conductor of heat.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A jewellery maker prefers to craft rings and bracelets from 18 carat gold, an alloy containing gold mixed with small amounts of silver, copper and zinc, rather than pure gold, because customers need jewellery that resists scratching and denting during daily wear.

   (a)

   A jewellery maker prefers to work with 18 carat gold, an alloy of gold with small amounts of silver, copper and zinc, rather than pure gold, because the alloy is harder and more resistant to scratching. What is an alloy?

   [1 mark]

   • AA pure metal with no other elements added
   • BA giant covalent structure containing only metal atoms
   • CA compound formed by ionic bonding between two metals
   • DA mixture of a metal with one or more other elements, usually other metals

   (b)

   The jewellery maker explains to a customer that pure gold is too soft for everyday jewellery, but the gold alloy is much harder. Why are alloys generally harder than the pure metals they are made from?

   [1 mark]

   • AAlloy atoms are smaller than pure metal atoms, packing more tightly together
   • BAlloys contain ionic bonds that pure metals do not have
   • CThe different sized atoms in an alloy distort the regular layers of the structure, making it harder for the layers to slide over each other
   • DAlloys have fewer delocalised electrons than pure metals

   (c)

   Explain, in terms of atomic structure, why pure gold can be bent and shaped relatively easily, but the 18 carat gold alloy used in jewellery is much harder and more resistant to scratching.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A structural engineer is selecting steel, an alloy of iron with carbon, as the main structural material for a new road bridge, instead of using pure iron, because the alloy provides a better balance of strength and flexibility for withstanding heavy traffic loads over decades.

   (a)

   A structural engineer is choosing steel, an alloy of iron with carbon, for the frame of a new bridge, instead of using pure iron. Explain why the delocalised electrons in a metallic structure, whether pure iron or a steel alloy, allow the metal to conduct electricity and heat, and describe how a metallic bond can be represented in a simple diagram.

   [3 marks]

   (b)

   The engineer must also explain in a technical report why pure iron, while an excellent conductor, would not be strong enough alone for the bridge's main load-bearing beams, and why adding carbon to make steel solves this problem, while noting one trade-off this can introduce.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A cookware manufacturer is choosing between pure aluminium and an aluminium alloy for the base of a new range of frying pans, needing a material that heats food quickly and evenly while surviving years of everyday kitchen use, including drops, scratches from metal utensils, and repeated heating and cooling.

   (a)

   A cookware manufacturer is deciding between using pure aluminium and an aluminium alloy for the base of a new range of frying pans, wanting a material that conducts heat quickly and evenly for cooking, but is also durable enough to withstand years of use, including being dropped, scratched by utensils and heated repeatedly. Explain, with reference to metallic bonding, why metals in general conduct heat well and can be bent into shape, and evaluate whether pure aluminium or an aluminium alloy would better meet the manufacturer's requirements.

   [6 marks]

   (b)

   The manufacturer's research and development team is also considering coating the alloy pan base with a thin layer of a different metal to further improve scratch resistance, and wants to understand more generally why metals differ so much from ionic and simple molecular substances in their physical properties. Compare metallic bonding with ionic bonding and covalent bonding in simple molecular substances, explaining why metals can be bent and shaped without shattering, unlike ionic compounds, and why metals generally conduct electricity as solids, unlike simple molecular covalent substances.

   [6 marks]

   Total for question 4: 12 marks

End of questions