To determine if a molecule is polar or nonpolar, follow these key steps:

1. Check for Polar Bonds
   • Identify if the molecule contains at least one polar covalent bond. A bond is polar if there is a significant difference in electronegativity between the bonded atoms, causing an uneven distribution of electron density

2. Draw the Lewis Structure
   • Sketch the molecule’s Lewis structure to understand how atoms are connected and where lone pairs of electrons are located

3. Determine Molecular Geometry
   • Use VSEPR (Valence Shell Electron Pair Repulsion) theory to figure out the three-dimensional shape of the molecule. The geometry affects how bond dipoles add up or cancel out

4. Analyze Symmetry and Dipole Moments
   • Visualize or draw the molecule’s shape and consider the direction of each bond’s dipole moment (vector).
   • If the dipole moments cancel out due to symmetrical arrangement, the molecule is nonpolar.
   • If the dipole moments do not cancel and create a net dipole moment, the molecule is polar

5. Look for Lone Pairs on the Central Atom
   • Lone pairs on the central atom often cause asymmetry, making the molecule polar

6. Special Cases
   • Molecules with identical atoms bonded symmetrically (e.g., O₂, N₂) are nonpolar even if bonds are polar.
   • Hydrocarbons (only C and H) are generally nonpolar due to similar electronegativities and symmetrical shapes

Summary Table

Step| What to Check| Result
---|---|---
1| Presence of polar bonds (electronegativity difference)| Necessary for polarity
2| Lewis structure and lone pairs| Lone pairs can cause polarity
3| Molecular geometry (VSEPR)| Determines symmetry
4| Net dipole moment (sum of bond dipoles)| Zero = nonpolar; nonzero = polar

Example

• Water (H₂O) is polar because it has polar O–H bonds and a bent shape due to lone pairs on oxygen, resulting in a net dipole moment

• Carbon dioxide (CO₂) has polar bonds but is linear and symmetrical, so dipoles cancel, making it nonpolar

This method allows you to predict molecular polarity by combining bond polarity and molecular shape considerations without complex calculations