Hydrogen chloride (HCl) and chlorine (Cl₂) are both covalently bonded molecules. Explain how a covalent bond is formed and describe the shapes of these two molecules, including their bond angles.

Edexcel A-Level Chemistry (9CH0) — 2.2 Covalent bonding and shapes · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Hydrogen chloride is a diatomic molecule formed between hydrogen and chlorine. Chlorine gas consists of diatomic molecules in which two chlorine atoms are bonded together.

Model answer (5 marks)

A covalent bond is formed when two non‑metal atoms share a pair of electrons. Each atom contributes one electron to the shared pair, creating a stable bond.

Both HCl and Cl₂ are diatomic molecules and therefore linear. The bond angle in each is 180°, as there are only two atoms bonded together.

Examiner tips

  • Use the phrase "share a pair of electrons" to show understanding of covalent bonding.
  • State that each atom contributes one electron to the shared pair.
  • Mention that both molecules are linear and give the bond angle 180°.
  • Keep the answer concise and to the point.

Common mistakes

  • Confusing covalent with ionic bonding.
  • Forgetting to mention that each atom contributes one electron.
  • Claiming a non‑linear shape or giving a different bond angle.

Mark scheme (5 marks)

  1. A covalent bond is formed by the sharing of a pair of electrons between two non-metal atoms.
  2. Each atom contributes one electron to the shared pair.
  3. HCl is a linear molecule.
  4. The bond angle in HCl is 180°.
  5. Cl₂ is also a linear molecule with a bond angle of 180°, because there are only two atoms bonded together / it is a diatomic molecule.

Key terms in this question

covalent bond · bond angle

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