Explain why metals are malleable and why alloys are generally less malleable than the pure metals from which they are formed.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
In a pure metal the positive ions are arranged in flat layers that can slide over each other. The delocalised electrons keep the ions attracted to each other even when the layers shift, so the structure does not break apart and the metal can be bent or hammered – it is malleable.
In an alloy atoms of different size are added. These atoms distort the regular lattice and disrupt the easy sliding of the layers. Because the layers can no longer move freely, the alloy is harder and less malleable than the pure metal.
In an alloy atoms of different size are added. These atoms distort the regular lattice and disrupt the easy sliding of the layers. Because the layers can no longer move freely, the alloy is harder and less malleable than the pure metal.
Examiner tips
- Use the terms "layers" and "delocalised electrons" to show understanding of the metallic bond.
- Explain how the lattice distortion in alloys reduces layer sliding.
- Keep the answer concise – 4 marks can be earned with two short sentences per point.
Common mistakes
- Confusing malleability with ductility or toughness.
- Failing to mention the role of delocalised electrons or lattice distortion.
- Using vague language such as "more rigid" without explaining the atomic basis.
Mark scheme (4 marks)
- In a pure metal, the positive ions (cations/kernels) are arranged in layers that can slide over one another.
- The delocalised electrons maintain electrostatic attraction to positive ions in any new position, so the structure does not break apart.
- In an alloy, atoms of different size are introduced, which distort/disrupt the regular lattice.
- This disruption prevents layers from sliding easily, making the alloy harder and less malleable than the pure metal.
Key terms in this question
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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