Dipole
Definition and meaning of Dipole in chemistry.
A dipole is a separation of positive and negative electric charge within a molecule or chemical bond, created when atoms share bonding electrons unequally due to a difference in electronegativity.
In more detail
Because the more electronegative atom pulls bonding electrons closer to itself, it develops a partial negative charge (δ−) while the other atom develops a partial positive charge (δ+). This charge separation is described quantitatively by the dipole moment (μ), a vector quantity pointing from the positive to the negative end of the charge distribution, measured in debyes (D) or coulomb-meters (C·m). A molecule's overall dipole moment is the vector sum of all its individual bond dipoles, so molecular shape matters as much as bond polarity: symmetric arrangements can cancel bond dipoles entirely, leaving a nonpolar molecule even though its bonds are polar.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | μ (mu) |
| SI Unit | coulomb-meter (C·m); commonly reported in debyes (D) |
| Example compound | H2O, μ ≈ 1.85 D |
In water (H2O), the O–H bonds are polar because oxygen is more electronegative than hydrogen, and the molecule's bent shape prevents the two bond dipoles from canceling, giving water a net dipole moment of about 1.85 D.
Frequently asked questions
Can a molecule have polar bonds but still be nonpolar overall?
Yes. In carbon dioxide (CO2), each C=O bond is polar, but the linear geometry places the two bond dipoles exactly opposite each other, so they cancel and the molecule has zero net dipole moment.
What is the difference between a bond dipole and a molecular dipole?
A bond dipole describes charge separation across a single bond, while the molecular dipole moment is the vector sum of all bond dipoles in the molecule, accounting for its three-dimensional shape.