Sodium chloride and hydrogen chloride both contain chlorine. Explain why sodium chloride is an ionic compound whilst hydrogen chloride is a covalent compound, referring to the type of atoms involved and the bonding that forms in each case.

Edexcel A-Level Chemistry (9CH0) — Topic 1 Foundations in chemistry · Explain · 5 marks · View as Markdown

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

Sodium chloride (NaCl) is a solid at room temperature that conducts electricity when dissolved in water. Hydrogen chloride (HCl) is a gas at room temperature that does not conduct electricity in its pure liquid form.

Model answer (5 marks)

Sodium chloride is an ionic compound because it is made from a metal (Na) and a non‑metal (Cl). The metal donates an electron to the non‑metal, giving Na⁺ and Cl⁻ ions that are held together by electrostatic attraction – an ionic bond.

Hydrogen chloride is a covalent compound because both atoms are non‑metals (H and Cl). They share a pair of electrons to satisfy the octet rule, forming a covalent bond.

Examiner tips

  • Use the terms ‘metal’ and ‘non‑metal’ to justify the type of bonding. Show the electron transfer for NaCl and electron sharing for HCl. Mention the resulting ionic or covalent bond.
  • Keep the answer concise – 5 marks can be earned with 2–3 short sentences.

Mark scheme (5 marks)

  1. Sodium is a metal and chlorine is a non-metal (in sodium chloride)
  2. In sodium chloride, electrons are transferred from sodium to chlorine, forming ions
  3. The oppositely charged ions are held together by electrostatic attraction (ionic bond)
  4. In hydrogen chloride, both hydrogen and chlorine are non-metals
  5. In hydrogen chloride, electrons are shared between the two atoms, forming a covalent bond

Related

More Foundations in chemistry questions

▶ Try answering this question with AI marking (free) →