Calcium chloride is an ionic compound used to de-ice roads in winter. Explain how an ionic bond forms when calcium reacts with chlorine to produce calcium chloride.

OCR A-Level Chemistry B: Salters (H433) — 2.1 Atoms, compounds, molecules and equations · Explain · 5 marks · View as Markdown

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

Calcium is a Group 2 metal. Chlorine is a Group 7 non-metal. When they react, each calcium atom reacts with two chlorine atoms to form one formula unit of calcium chloride, CaCl₂.

Model answer (5 marks)

Calcium loses two electrons from its outer shell.
Each chlorine atom gains one electron into its outer shell.
Calcium therefore forms a 2+ ion.
Each chlorine atom forms a 1− ion.
The oppositely charged ions are held together by strong electrostatic forces, forming an ionic bond.

Examiner tips

  • Use the word ‘loses’ and ‘gains’ to show electron transfer. Show the charge on each ion explicitly. Explain that the attraction between opposite charges creates the ionic bond.
  • common_mistakes
  • :
  • Saying calcium ‘gains’ electrons or chlorine ‘loses’ electrons. Forgetting to state the charges on the ions. Using vague terms like ‘bond’ without mentioning electrostatic attraction.

Mark scheme (5 marks)

  1. Calcium loses two electrons (from its outer shell)
  2. Each chlorine atom gains one electron (into its outer shell)
  3. Calcium forms a 2+ ion (positively charged ion)
  4. Each chlorine forms a 1− ion (negatively charged ion)
  5. The oppositely charged ions are held together by strong electrostatic forces (forming an ionic bond)

Key terms in this question

ionic bond · ion · ionic compound

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