Explain why carbon dioxide (CO₂) is a non-polar molecule despite containing two polar covalent bonds.

IB DP Chemistry Standard Level (2023 syllabus) — S2.2 The covalent model · Explain · 4 marks · View as Markdown

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

Model answer (4 marks)

The C=O bonds are polar because oxygen is more electronegative than carbon.
CO₂ is linear.
There are no lone pairs on the central carbon, so the two bond dipoles point in exactly opposite directions.
The equal and opposite dipoles cancel, giving a net dipole moment of zero – the molecule is non‑polar.

Examiner tips

Use the word ‘polar’ for the bonds and ‘non‑polar’ for the molecule. Mention the linear geometry and lack of lone pairs. Show the cancellation of dipoles explicitly.

Common mistakes

Saying the molecule is polar because it has polar bonds. Forgetting to mention the linear shape or the absence of lone pairs. Using vague terms like ‘symmetrical’ without linking to dipole cancellation.

Mark scheme (4 marks)

The C=O bonds are polar due to the difference in electronegativity between carbon and oxygen.
CO₂ has a linear shape/geometry.
There are no lone pairs on the central carbon atom, so the two bond dipoles point in exactly opposite directions.
The two equal and opposite bond dipoles cancel, so the net/overall dipole moment is zero and the molecule is non-polar.

Key terms in this question

polar covalent bond · non-polar molecule