AQA GCSE Combined Science (8464), Higher tier · Chemistry › Bonding, structure, and the properties of matter › How bonding and structure are related to the properties of
Practise Metals as conductors. 12 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Why metals are good conductors of electricity and of thermal energy: both depend on the delocalised electrons. Questions are often 2 marks on their own, or part of a comparison with ionic compounds, graphite or covalent substances.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
State that metals conduct electricity and heatMetals are good conductors of electricity and of thermal energy.
4
Name the particles that carry the chargeDelocalised electrons carry electrical charge through the metal.
5
Explain electrical conduction in metalsThe delocalised electrons are free to move through the structure, carrying charge.
6
Explain thermal conduction in metalsEnergy is transferred through the metal by the delocalised electrons.
7
Compare conduction in metals and ionic compoundsMetals conduct when solid because electrons move; ionic compounds conduct only when molten or dissolved, because ions move.
Notes
Conducting electricity
An electric current is a flow of charge. A substance conducts if it has charged particles that are free to move.
In a metal, the outer shell electrons are delocalised: they are free to move through the whole structure.
In a circuit, the delocalised electrons move through the metal and carry electrical charge. So metals are good conductors of electricity.
This works whether the metal is solid or molten, because the delocalised electrons are always there.
Conducting thermal energy
Metals are also good conductors of thermal energy.
The delocalised electrons move through the structure and transfer energy quickly from hotter parts of the metal to cooler parts.
This is why pans are made of metal, and why a metal object feels cold to touch: it conducts energy away from your hand quickly.
Comparing conductors
Metals: conduct when solid or liquid; delocalised electrons move.
Graphite: conducts as a solid; like a metal, it has delocalised electrons.
Ionic compounds: conduct only when molten or dissolved in water; ions move.
Small molecules, polymers, diamond and silicon dioxide: do not conduct, because no charged particles are free to move.
Copper is used for electrical wires because it is a very good conductor and can be drawn out into wires.
Cheatsheet
Metals conduct electricity: delocalised electrons carry charge through the metal
Metals conduct thermal energy: energy is transferred by the delocalised electrons
To conduct electricity: charged particles that are free to move
Metal (solid or liquid): electrons move. Ionic compound (molten or dissolved): ions move
Graphite conducts because it has delocalised electrons, like a metal
How to answer each type of question
Explain why a metal conducts electricity
2 marks5
Name the particles: delocalised electrons.
Say they are free to move through the structure and carry charge.
Example. Explain why copper is a good conductor of electricity.
Show the model answer
Copper has delocalised electrons (1), which are free to move through the metal and carry electrical charge (1).
Explain why a metal is a good thermal conductor
2 marks6
Name the particles: delocalised electrons.
Say they transfer energy through the metal.
Example. Saucepans are often made of aluminium. Explain why aluminium is a good conductor of thermal energy.
Show the model answer
Aluminium has delocalised electrons (1). These move through the metal and transfer energy quickly (1).
Compare conduction in different substances
4 marks7
For each substance, name the particles that could carry charge.
Say whether those particles are free to move in the state described.
Conclude whether each substance conducts.
Example. Explain why solid magnesium conducts electricity but solid magnesium chloride does not.
Show the model answer
Magnesium has delocalised electrons (1), which are free to move through the structure and carry charge (1). In solid magnesium chloride, the ions are held in fixed positions in the lattice (1), so there are no charged particles free to move (1).
Shortcuts and memory tricks
Electricity and heat in metals have the same answer: delocalised electrons.
Ask 'what moves?': electrons in metals and graphite; ions in molten or dissolved ionic compounds; nothing in molecular substances.
Delocalised = not stuck to one atom = free to move.
Where marks are lost
Saying ions move in a metal. The positive ions stay in place; the delocalised electrons move.
Saying 'electrons carry the current' without saying they are delocalised or free to move.
Forgetting the delocalised electrons when explaining thermal conduction: the specification links it to them.
Writing 'free electrons' on its own. Use 'delocalised electrons' to be safe.
Exam technique
Conduction answers need two points: the particle (delocalised electrons) and what it does (moves through the structure, carrying charge or energy).
In comparison questions, write a sentence about each substance; don't leave the examiner to work out the second half.
Use 'charge' for electrical conduction and 'energy' for thermal conduction.
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Metals are good conductors of electricity.
(a) Why are metals good conductors of electricity? Tick (✓) one box.[1]
Delocalised electrons carry charge through the metal.
Ions move through the metal.
Metal atoms are shiny.
Metals have high melting points.
(b) Give one use of copper that depends on it being a good conductor of electricity.[1]
(c) Which of these substances does not conduct electricity when it is solid? Tick (✓) one box.[1]
Aluminium
Copper
Graphite
Sodium chloride
(d) A saucepan is made of steel and has a plastic handle. Suggest why.[2]
Show the answer and mark scheme
(a)Answer: Delocalised electrons carry charge through the metal.
(b)Answer: electrical wires / cables
electrical wires / cables / circuit connections
(c)Answer: Sodium chloride
(d)Answer: Steel conducts thermal energy well, so it heats the food; plastic is a poor conductor, so the handle stays cool enough to hold.
steel is a good (thermal) conductor so it transfers energy to the food
plastic is a poor conductor / insulator so the handle stays cool (safe to hold)
Question 2Medium6 marks
Copper is used for electrical wiring and for the bases of some saucepans.
(a) Explain why solid copper conducts electricity but solid copper(II) chloride does not.[3]
(b) Explain how thermal energy is transferred through a metal.[2]
(c) Aluminium is used for overhead power cables, even though copper is a better conductor. Suggest one reason why.[1]
Show the answer and mark scheme
(a)Answer: Copper has delocalised electrons that move through the structure carrying charge; in solid copper(II) chloride the ions are fixed and there are no delocalised electrons.
copper has delocalised electrons
which move through the structure and carry (electrical) charge
in solid copper(II) chloride the ions are in fixed positions / cannot move (and there are no delocalised electrons)
(b)Answer: Delocalised electrons gain kinetic energy and move through the metal, transferring energy to other particles.
delocalised electrons gain (kinetic) energy
they move through the metal and transfer the energy (to other particles)
(c)Answer: Aluminium has a lower density, so the cables are lighter.
aluminium has a lower density / is lighter / is cheaper
Question 3Hard5 marks
An engineer needs to choose a metal for a heat sink, a part that must conduct thermal energy away from a hot electronic component as quickly as possible.
(a) Describe an experiment the engineer could do to compare how well rods of different metals conduct thermal energy.[3]
(b) Explain how thermal energy is transferred through a metal.[2]
Show the answer and mark scheme
(a)Answer: Use rods of the same size of each metal, with a pin attached near one end of each rod using a small amount of wax; heat the other ends in the same way at the same time and time how long it takes for each pin to fall. The shortest time shows the best conductor.
use rods of the same length and diameter, each with a pin attached near one end using a small blob of wax
heat the other end of each rod in the same way (e.g. in the same hot water bath, at the same time)
time how long it takes for each pin to fall: the shortest time shows the best thermal conductor
(b)Answer: The delocalised electrons gain energy at the hot end, move through the metal and transfer the energy to other particles further along.
the delocalised electrons gain (kinetic) energy where the metal is hot
the delocalised electrons move through the metal and transfer the energy to other parts / particles