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ChemistryInternational GCSEEdexcel & Cambridge IGCSEYears 10–11

IGCSE Chemistry Covalent Bonding Notes

Covalent bonding is the sharing of pairs of electrons between non-metal atoms. It forms simple molecules such as H₂O and CH₄, and giant structures such as diamond.

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Key concepts

Single covalent bond
One shared pair of electrons, e.g. H–H, H–Cl.
Double / triple bond
Two or three shared pairs, e.g. O=O, N≡N.
Simple molecular
Small discrete molecules with weak forces between them, giving low melting points.
Giant covalent
Huge networks of covalent bonds (diamond, graphite, silicon dioxide) with very high melting points.
  • Simple molecular substances do not conduct electricity — no free electrons or ions.
  • Graphite conducts but diamond does not; graphite has delocalised electrons between layers.
  • Silicon dioxide has a giant covalent structure similar to diamond.
  • Fullerenes and nanotubes are covalent structures of carbon with useful properties.

Worked example

Draw a dot-and-cross diagram for water (H₂O).

  1. 1Oxygen has 6 outer electrons; each H has 1 outer electron.
  2. 2Oxygen shares one pair with each H, forming two O–H single bonds.
  3. 3Show two shared pairs (one dot + one cross each) and the two lone pairs on oxygen.

Answer: O has 2 bond pairs (H) and 2 lone pairs, so H₂O has 8 outer electrons on O.

Common mistakes

✗ Showing electrons transferred rather than shared.

✓ Covalent bonding is sharing; transfer is ionic.

✗ Missing lone pairs on the central atom.

✓ Include all non-bonding electron pairs to make outer shells add up correctly.

✗ Confusing weak intermolecular forces with the covalent bond.

✓ Melting simple molecular substances only breaks weak forces between molecules, not the covalent bonds inside them.

Quick check

Try these, then reveal the answers.

How many covalent bonds does nitrogen typically form?Reveal answer

3 (it has 5 outer electrons and needs 3 more).

Why doesn't methane conduct electricity?Reveal answer

No free electrons and no ions; all electrons are held in bonds.

Give one use of graphite that depends on its structure.Reveal answer

Electrodes / pencil 'lead' / lubricant — layers slide and delocalised electrons carry charge.

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Exam tips

  • Show shared electrons clearly using one dot and one cross per pair.
  • For giant covalent, link property (hard, high melting) to 'many strong covalent bonds must be broken'.
  • Compare graphite and diamond by structure, then property, then use.

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Related topics

Bonding and StructureIonic Bonding

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

What is a covalent bond?+

A shared pair of electrons between two atoms, holding them together by attraction between the shared electrons and both nuclei.

Why are simple molecular substances often gases at room temperature?+

Weak intermolecular forces need very little energy to overcome, so they melt and boil at low temperatures.

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