GCSE Chemistry Covalent Bonding Notes
Covalent bonds form when non-metal atoms share pairs of electrons. The type of covalent structure (simple molecular or giant) explains the properties.
Key concepts
- Covalent bond
- A shared pair of electrons between two non-metal atoms.
- Simple molecular
- Small molecules (e.g. H₂O, CO₂) held together by weak intermolecular forces — low melting points, do not conduct.
- Giant covalent
- Huge networks (e.g. diamond, graphite, silicon dioxide) with strong bonds throughout — very high melting points.
- Melting a simple molecular substance breaks weak intermolecular forces, not the covalent bonds.
- Diamond is hard because every carbon forms 4 strong covalent bonds in a rigid 3D lattice.
- Graphite conducts because each carbon has 3 bonds and one delocalised electron per atom.
Worked example
Explain why the melting point of chlorine (Cl₂) is very low but the melting point of silicon dioxide (SiO₂) is very high.
- 1Cl₂ is simple molecular — small molecules held together by weak intermolecular forces.
- 2Little energy is needed to overcome these forces, so its melting point is low.
- 3SiO₂ is a giant covalent structure — every atom is held by strong covalent bonds.
- 4Huge amounts of energy are needed to break these bonds, so its melting point is high.
Answer: Cl₂ has weak intermolecular forces; SiO₂ has strong covalent bonds throughout its giant lattice.
Common mistakes
✗ Saying you break covalent bonds when melting a simple molecular substance.
✓ You break the weak intermolecular forces between molecules.
✗ Claiming all covalent substances have low melting points.
✓ Giant covalent (diamond, silica) have very high melting points.
✗ Missing shared electrons in dot-and-cross diagrams.
✓ Show the shared pair in the overlap between atoms.
Quick check
Try these, then reveal the answers.
What is shared in a covalent bond?Reveal answer
A pair of electrons.
Why does graphite conduct?Reveal answer
It has delocalised electrons that can move.
Why is diamond hard?Reveal answer
Every carbon forms 4 strong covalent bonds in a rigid 3D lattice.
Exam tips
- Always distinguish 'covalent bonds' (strong) from 'intermolecular forces' (weak).
- Link structure to properties: simple molecular → low mp; giant covalent → high mp.
- For graphite, mention 3 bonds per carbon and 1 delocalised electron.
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Frequently asked questions
Do covalent compounds conduct electricity?+
Generally no — there are no charged particles free to move (graphite is the notable exception).
Why do simple molecular substances have low melting points?+
Only weak intermolecular forces between molecules need to be overcome to melt them.
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