Molecular Polarity
Molecular polarity describes the distribution of electric charge across a molecule, determined by bond polarity and molecular symmetry.
Molecular Polarity
A molecule is polar if it has a net dipole moment — an uneven distribution of electric charge.
What Makes a Bond Polar?
When two atoms with different electronegativities form a bond, the shared electrons are pulled toward the more electronegative atom:
Electronegativity difference (ΔEN):
- ΔEN < 0.4 — non‑polar covalent
- 0.4 ≤ ΔEN < 1.7 — polar covalent
- ΔEN ≥ 1.7 — ionic
Symmetry Matters
Even a molecule with polar bonds can be non‑polar overall if the bond dipoles cancel by symmetry:
| Molecule | Polar Bonds? | Geometry | Overall Polarity |
|---|---|---|---|
| CO₂ | Yes (C=O) | Linear, symmetric | Non‑polar ✅ |
| CH₄ | Slight (C–H) | Tetrahedral, symmetric | Non‑polar ✅ |
| H₂O | Yes (O–H) | Bent, asymmetric | Polar ⚡ |
| NH₃ | Yes (N–H) | Trigonal pyramidal | Polar ⚡ |
Why Polarity Matters
- Solubility — "Like dissolves like": polar solutes dissolve in polar solvents (e.g., ethanol in water).
- Boiling point — Polar molecules have stronger intermolecular forces, raising boiling points.
- Biological function — Cell membranes use a phospholipid bilayer to separate polar environments.
Related molecules: Water (polar), Carbon Dioxide (non‑polar), Ammonia (polar)
Try the tool: Lewis Structure Visualizer