IGCSE Chemistry Bonding and Structure Notes
The properties of any substance come from the bonding between its particles. IGCSE focuses on three types of bonding and the structures they form.
Key concepts
- Ionic bonding
- Electrons transfer from a metal to a non-metal, forming oppositely charged ions in a giant lattice.
- Covalent bonding
- Shared pairs of electrons between non-metal atoms, forming simple molecules or giant covalent structures.
- Metallic bonding
- A lattice of positive metal ions surrounded by a sea of delocalised electrons.
- Giant vs simple structures
- Giant structures have high melting points; simple molecular substances have low melting points.
- Ionic compounds conduct when molten or dissolved (ions free to move), not when solid.
- Diamond and graphite are both giant covalent structures made only of carbon.
- Graphite conducts electricity because each carbon has one delocalised electron.
- Metals are malleable because layers of ions can slide over one another.
Worked example
Explain why magnesium oxide has a very high melting point.
- 1MgO is an ionic compound with a giant ionic lattice.
- 2Mg²⁺ and O²⁻ ions have high charges.
- 3Strong electrostatic forces of attraction act between the oppositely charged ions.
- 4A large amount of energy is needed to overcome these forces, so the melting point is high.
Answer: Strong electrostatic forces between Mg²⁺ and O²⁻ ions in the giant lattice require lots of energy to break.
Common mistakes
✗ Writing that covalent bonds are broken when a simple molecular substance melts.
✓ Only weak intermolecular forces break; the strong covalent bonds inside molecules stay intact.
✗ Saying metals conduct because ions move.
✓ Metals conduct because delocalised electrons move through the lattice.
✗ Confusing giant covalent (diamond, silica) with simple covalent (H₂O, CH₄).
✓ Look for a repeating 3D network — that is giant covalent; discrete molecules are simple molecular.
Quick check
Try these, then reveal the answers.
What holds a giant ionic lattice together?Reveal answer
Strong electrostatic forces of attraction between oppositely charged ions.
Why does diamond not conduct electricity but graphite does?Reveal answer
Diamond uses all 4 outer electrons in bonds; graphite has one delocalised electron per carbon.
Which type of substance has the lowest melting point: ionic, giant covalent or simple molecular?Reveal answer
Simple molecular.
Exam tips
- Match structure to property: melting point, conductivity, solubility, hardness.
- Use 'strong electrostatic forces of attraction between oppositely charged ions' word-for-word for ionic bonding.
- For metals, mention 'delocalised electrons' for both conductivity and malleability.
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Frequently asked questions
Why do simple molecular substances have low melting points?+
Only weak intermolecular forces need to be overcome when they melt; the strong covalent bonds within molecules are not broken.
What is a delocalised electron?+
An outer-shell electron that is not attached to a specific atom and is free to move through a metallic lattice.
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