Explain why most metals have high densities and why alloying a metal with another element can make it harder than the pure metal.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Metal atoms or ions are arranged in a closely packed, regular lattice.
This close packing means a large mass occupies a small volume, giving the metal a high density.
When a metal is alloyed with another element, atoms of different sizes are introduced into the lattice.
The differently sized atoms disturb the regular arrangement and prevent layers of atoms from sliding over one another, so the alloy is harder (less malleable) than the pure metal.
This close packing means a large mass occupies a small volume, giving the metal a high density.
When a metal is alloyed with another element, atoms of different sizes are introduced into the lattice.
The differently sized atoms disturb the regular arrangement and prevent layers of atoms from sliding over one another, so the alloy is harder (less malleable) than the pure metal.
Examiner tips
- Use the term ‘closely packed lattice’ to show understanding of density. Mention that alloying introduces size mismatch to explain hardness. Keep the answer concise and directly linked to the mark scheme points. Use UK spelling (e.g., ‘malleable’).
Common mistakes
- Confusing density with hardness. Saying alloying always makes a metal softer. Using vague phrases like ‘more atoms’ instead of ‘different sized atoms’.
Mark scheme (4 marks)
- Metal atoms/ions are closely packed together (in a regular arrangement/lattice)
- This close packing means a large mass occupies a small volume, giving high density
- In an alloy, atoms/ions of different sizes are introduced into the lattice
- The differently sized atoms prevent layers of atoms from sliding over one another, so the alloy is harder/less malleable than the pure metal
Key terms in this question
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →