2.2.6—Molecular polarity
- Syllabus
- First assessment 2025
- Objective
- 2.2.6
- Level
- HL
Molecular Polarity
Molecular polarity depends on both the polarity of individual bonds and the three-dimensional geometry of the molecule or ion. Bond dipoles can cancel or produce a net dipole moment.
Draw or infer the geometry, place each bond dipole, and check whether the vector sum is zero. Do not decide molecular polarity from a single bond alone.
CO₂ contains polar C=O bonds, but their equal opposite dipoles cancel in a linear molecule. In bent H₂O they do not cancel, so the molecule has a net dipole. Always establish the three-dimensional geometry before adding dipoles as vectors.
Predicting Molecular Polarity
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Explain the polarity of the SO2 molecule.
«both» bonds are polar / electronegativity difference «between O and S»
«bond» dipoles do not cancel each other / there is a net dipole «because bonds are at an angle less than 180∘ »
Marking guidance:
Accept unsymmetrical distribution of charge OR dipoles add to give a «partial» positive «charge» on S and a «partial» negative «charge» on the O atoms for M2.
Apply ECF from molecular geometry.
The Covalent Model Summary
Retrieve the covalent pathway: shared pairs and bond order lead to geometry, polarity and molecular polarity; structure determines network properties, IMF behaviour and chromatography; HL representations extend to resonance, formal charge, sigma/pi bonds and hybridization.
Check the representation first, then count domains, apply geometry, identify polarity or forces, and connect the structure to the requested property or HL bonding description.