Debye
Definition and meaning of Debye in chemistry.
Debye (symbol D) is a non-SI unit of electric dipole moment used to describe how polar a molecule is. One debye equals 3.336 × 10⁻³⁰ coulomb-meters (C·m).
In more detail
A molecule's dipole moment reflects the separation of positive and negative charge across its structure, arising from differences in electronegativity between bonded atoms combined with molecular geometry. Larger debye values indicate greater polarity, which influences properties such as boiling point, solubility, and intermolecular forces (especially dipole-dipole interactions and hydrogen bonding). Dipole moments are experimentally determined from microwave spectroscopy or from a substance's dielectric constant, and they help predict whether a molecule will be polar or nonpolar overall, since bond dipoles can partially or fully cancel depending on molecular symmetry.
Key facts
| Symbol | D |
|---|---|
| SI Equivalent | 1 D = 3.336 × 10⁻³⁰ C·m |
| Named After | Peter Debye (1884–1966), Nobel Prize in Chemistry, 1936 |
| Field | Physical Chemistry |
The water molecule (H2O) has a permanent dipole moment of 1.85 D, arising from its bent geometry and the polar O-H bonds, which do not cancel.
Frequently asked questions
Is the debye an SI unit?
No. The debye is a non-SI unit retained for convenience in chemistry because molecular dipole moments in C·m would involve inconveniently small numbers; the SI unit of dipole moment is the coulomb-meter.
Does a nonzero bond dipole always mean a molecule has a net dipole moment?
No. Individual bond dipoles can cancel due to molecular symmetry, as in CO2, giving a net dipole moment of zero even though each C=O bond is polar.