Question Constellation Sign up for free AQA · GCSE · Chemistry · Higher
Atomic layers in iron alloys
Pure iron is too soft for many uses.
Explain why mixing iron with other metals makes alloys which are harder than pure iron.
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Marking points
- 1 Identifies different-sized atoms/metal ions in the alloy.
- 2 Explains that these distort the regular layers.
- 3 Links the distortion to layers/atoms being unable to slide easily.
Full-mark answer
Atoms of the added metals have different sizes from iron atoms. They distort the regular layers in the structure, so the layers of atoms cannot slide over one another easily and the alloy is harder.
Why this answer loses marks
The added metal fills the gaps, so the alloy is heavier.
Hardness comes from different atom sizes distorting layers and blocking their movement.