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ChemistryGCSEAQA & EdexcelYears 10–11

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.

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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.

  1. 1Cl₂ is simple molecular — small molecules held together by weak intermolecular forces.
  2. 2Little energy is needed to overcome these forces, so its melting point is low.
  3. 3SiO₂ is a giant covalent structure — every atom is held by strong covalent bonds.
  4. 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.

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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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Key terms explained

Short, exam-ready definitions with a formula, a worked example and an examiner tip.

What is covalent bond?What is mole?Full glossary

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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