Iron is a metal with a giant metallic structure. It is used to make steel railway tracks because of its high melting point and strength. Explain, in terms of structure and bonding, why iron has a high melting point and why it is able to be bent into shape without shattering.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Iron has a giant metallic structure consisting of a lattice of positive ions surrounded by a sea of delocalised electrons. Railway engineers value iron-based metals for their ability to withstand high temperatures and to be shaped without cracking.
Model answer (4 marks)
Iron consists of a lattice of Fe^+ ions surrounded by a sea of delocalised electrons. The electrons are attracted to all the positive ions, giving strong electrostatic forces of attraction between the ions and the electron cloud. A large amount of energy is required to break these forces, so iron has a high melting point. The positive ions are arranged in layers that can slide over one another while the delocalised electrons keep the structure together, allowing the metal to be bent without shattering.
Examiner tips
- Use the phrase ‘lattice of positive ions surrounded by delocalised electrons’
- Explain that strong electrostatic attraction gives a high melting point
- Mention that layers can slide while electrons maintain bonding for ductility
Common mistakes
- Confusing the role of electrons with covalent bonds
- Failing to link high melting point to strong ionic‑electron attraction
- Describing iron as a crystal of covalent bonds rather than a metallic lattice
Mark scheme (4 marks)
- Iron consists of a lattice of positive ions surrounded by delocalised (free) electrons
- There are strong electrostatic forces of attraction between the positive ions and the delocalised electrons
- A large amount of energy is needed to overcome these strong forces / bonds, so the melting point is high
- The layers of positive ions can slide over one another (without breaking the metallic bonding / whilst the delocalised electrons maintain the structure), so the metal can be bent without shattering
Key terms in this question
giant metallic structure · melting point
Related
- All Pearson Edexcel International GCSE Chemistry (4CH1) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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