What Makes a Molecule Polar?
A polar molecule has an unequal distribution of electric charge, resulting in a net dipole moment.
Electronegativity Difference
When two atoms with significantly different electronegativities form a bond, the more electronegative atom pulls electron density toward itself. This creates a partial negative charge (δ−) on one end and a partial positive charge (δ+) on the other — a polar bond.
Molecular Geometry Matters
Even if a molecule contains polar bonds, it can still be nonpolar if its geometry is symmetrical enough to cancel all bond dipoles. The shape of the molecule is just as important as the bonds themselves.
Net Dipole Moment
A molecule is polar when its bond dipoles do not cancel. The vector sum of all bond dipoles produces a net dipole moment (measured in Debye). A nonzero dipole moment means the molecule is polar.