Chemistry · General chemistry I · Worked example
Compare the polarity of CO₂ and water
Both CO₂ and H₂O have polar bonds. Why is CO₂ nonpolar while water is polar?
Count the domains in CO₂
Carbon has two double bonds and no lone pairs. Each double bond is one domain, so there are two.
Shape of CO₂
Two domains sit on opposite sides: CO₂ is linear, with a 180° angle.
Shape of water
Oxygen has two bonds and two lone pairs, four domains, so water is bent.
Add the bond dipoles
In CO₂ the two carbon–oxygen dipoles point in exactly opposite directions and cancel. In water both oxygen–hydrogen dipoles point partly toward the oxygen side, so they add to a net dipole.
Result
CO₂ is linear, so its bond dipoles cancel; water is bent, so they add. Molecular shape, not bond polarity alone, decides.
Your turn
Is carbon tetrachloride, CCl₄, polar?
Show the answer and explanation
No.
Carbon has four bonds and no lone pairs, so CCl₄ is tetrahedral. Its four identical C–Cl dipoles point to the corners of the tetrahedron and cancel, so the molecule is nonpolar even though each bond is polar.
Keep exploring
In VSEPR & molecular polarity, replace one oxygen with sulfur. Carbonyl sulfide, OCS, is still linear, but its two bond dipoles are unequal, so they no longer cancel and the molecule is polar.
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