Dipole Moment
Definition and meaning of Dipole Moment in chemistry.
Dipole moment is a vector quantity that measures the separation of positive and negative electric charge in a molecule, indicating both the magnitude and direction of its overall polarity.
In more detail
A dipole moment arises when bonded atoms differ in electronegativity, pulling shared electrons toward the more electronegative atom and creating partial charges (δ+ and δ−). The molecular geometry matters as much as bond polarity: individual bond dipoles are vectors, so they can add up or cancel depending on molecular shape. Dipole moment strongly influences physical properties such as boiling point, solubility, and the strength of intermolecular dipole-dipole forces. It is typically reported in debye units (D), where 1 D = 3.336 × 10⁻³⁰ coulomb-meters.
Key facts
| Symbol | μ (mu) |
|---|---|
| SI unit | coulomb-meter (C·m) |
| Common unit | debye (D); 1 D = 3.336 × 10⁻³⁰ C·m |
| Field | Physical Chemistry |
Water (H2O) has a dipole moment of about 1.85 D because its bent geometry prevents the two polar O–H bond dipoles from canceling, whereas linear carbon dioxide (CO2) has polar C=O bonds but a net dipole moment of zero due to their symmetric, opposing arrangement.
Frequently asked questions
Can a molecule with polar bonds have zero net dipole moment?
Yes. If the molecular geometry is symmetric, the individual bond dipole vectors cancel out, as in CO2 and CCl4, even though each bond is individually polar.
How is dipole moment measured experimentally?
It is commonly determined from a substance's dielectric constant response to an applied electric field, or from the Stark effect observed in microwave rotational spectroscopy.