# What Is the Debye?

Liz Thomas

The Debye is a unit of measurement named after physicist Peter Debye. This measurement refers to the electric dipole moment, providing a standard measurement unit for these dipole moments. The symbol for this unit is D. The numeric measurement for one D is 1x10-18 statcoulomb-centimeter. D is not part of the international system of units.

A dipole moment is the overall measurement of charges in a molecule, known as the overall polarity. A molecule will contain negative charges because of the electrons and positive charges due to the protons. A vector is formed that runs from the negative charge to the positive charge. In particular, the dipole moment refers to the positions or orientation of the charges.

Specifically, the Debye is a measurement of a diatomic molecule. The two charges in the diatomic molecule are separated by a distance of one angstrom. The two charges have a measurement of 10-10 franklins or statcoulombs.

Diatomic molecules that have the same molecules, such as oxygen gas (O2), hydrogen gas (H2) and chlorine gas (Cl2), have no dipole moment. Molecules with more than two atoms will also have no dipole moment, if the atoms are located in a linear arrangement, such as the molecule carbon dioxide (CO2). Symmetrical molecules, such as methane (CH4), will also have no dipole moment.

The strength of the dipole moment will depend on the atoms in the molecule and the arrangement or structure of these atoms. Molecules that contain two different atoms, such as hydrochloric acid (HCl), will have a dipole moment. Other molecules with dipole moments are those that have a bent or angular arrangement. Water (H2O) is a good example of a bent structure. The angle formed by the two hydrogen molecules bound to oxygen is 107.5 degrees.

D is not an SI unit but a centimeter gram second (CGS) unit. When dipole moments are measured using SI units, the resulting numbers are very large. In place of SI units, this measurement was developed to keep numbers small, which makes calculations less cumbersome.

This unit of measurement was named after Peter Debye, who was born in 1884 and died in 1966. He was a Dutch physicist who was known for research conducted on polar molecules. His other discoveries include the Debye model, which estimates how much a phonon contributes to a solid's specific heat. He also developed the Debye frequency that calculates the maximum vibration frequency of crystal atoms.