Ionic, covalent and metallic bonding — Edexcel GCSE Chemistry revision

Three bond types

• Ionic: metal gives electrons to a non-metal; oppositely charged ions attract in a giant lattice.
• Covalent: non-metals share pairs of electrons.
• Metallic: positive metal ions in a sea of delocalised electrons.

Properties follow structure

• Ionic compounds have high melting points and conduct only when molten or dissolved (ions must move).
• Simple molecules have low melting points because the weak intermolecular forces break, not the bonds.
• Giant covalent (diamond, graphite, silicon dioxide) melt very high; graphite conducts because of delocalised electrons.
• Metals conduct and are malleable because layers slide and electrons are free to move.

Key terms

Delocalised electron

An electron free to move through a structure.

Intermolecular force

A weak attraction between separate molecules.

Giant lattice

A huge regular 3D arrangement of ions or atoms.

Giant covalent structure

A huge lattice of atoms joined by strong covalent bonds, e.g. diamond, graphite, silicon dioxide.

Delocalised electrons

Electrons free to move through a structure, carrying charge or heat, e.g. in metals or graphite.

Simple molecular substance

Substance made of small molecules held by weak intermolecular forces, with strong covalent bonds within molecules.

Common exam traps

• Saying you break covalent bonds when melting a simple molecular substance — you break intermolecular forces.
• Saying ionic solids conduct — they only conduct when molten or in solution.
• Forgetting graphite has one carbon atom bonded to three others, leaving one delocalised electron.

Practice questions with answers

1. 1. Why does sodium chloride only conduct electricity when molten or dissolved?

   • • The ions gain charge
   • • The ions become free to move
   • • New electrons are made
   • • Covalent bonds break

   Answer: The ions become free to move

   Conduction needs charged particles that can move.

2. 2. Which structure has a low melting point?

   • • Diamond
   • • Sodium chloride
   • • Carbon dioxide
   • • Copper

   Answer: Carbon dioxide

   It is a simple molecule with weak forces between molecules.

3. 3. Explain why metals are malleable.

   Answer: Layers of identical positive ions can slide over each other without breaking the metallic bonding.

   Mention layers sliding for the mark.

4. 4. Why does graphite conduct electricity but diamond does not?

   Answer: Each carbon in graphite bonds to three others, leaving one delocalised electron; in diamond all four are used in bonds.

   Conduction needs free-moving charged particles.

5. 5. Which type of bonding involves the transfer of electrons?

   • • Ionic
   • • Covalent
   • • Metallic
   • • Van der Waals

   Answer: Ionic

   Ionic bonding involves a metal transferring electrons to a non-metal, forming oppositely charged ions.

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