Explain why metals can be drawn into wires (are ductile) and why a metal's electrical conductivity decreases when it is alloyed with another metal of different atomic radius.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Metals are ductile because the lattice of positive ions is surrounded by a sea of delocalised electrons. When a stress is applied the ion layers can slide past one another without breaking the metallic bonds, as the electrons move with the layers and keep the electrostatic attraction.
Electrical conductivity is high in a pure metal because the delocalised electrons can move freely through the regular lattice and carry charge.
When a metal is alloyed with another metal of a different atomic radius the lattice is distorted. The size mismatch scatters or impedes the flow of delocalised electrons, so the electrical conductivity decreases.
Electrical conductivity is high in a pure metal because the delocalised electrons can move freely through the regular lattice and carry charge.
When a metal is alloyed with another metal of a different atomic radius the lattice is distorted. The size mismatch scatters or impedes the flow of delocalised electrons, so the electrical conductivity decreases.
Examiner tips
- Use the phrase "sea of delocalised electrons" and link it to ductility and conductivity.
- Show the two parts of the answer: ductility explanation first, then conductivity change.
- Mention lattice distortion due to size mismatch for the alloy part.
Common mistakes
- Confusing ductility with malleability or saying only the ions move.
- Forgetting to mention the role of delocalised electrons in maintaining attraction during sliding.
- Not specifying that the alloying atoms distort the lattice and scatter electrons.
Mark scheme (4 marks)
- In a metal, a lattice of positive ions (cations) is surrounded by / immersed in a 'sea' of delocalised electrons.
- When a stress is applied, layers of ions can slide past one another without disrupting the overall metallic bonding, because the delocalised electrons can move with the layers and maintain the electrostatic attraction.
- In a pure metal, electrical conductivity is high because the delocalised electrons can move freely through the regular lattice and carry charge.
- In an alloy, atoms of different size distort the lattice, which scatters / impedes the flow of delocalised electrons, reducing electrical conductivity.
Key terms in this question
alloy · electrical conductivity
Related
- All IB DP Chemistry Standard Level (2023 syllabus) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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