- Orientational Polarization Definition: Orientational polarization is the alignment of permanent dipole moments in molecules along the direction of an applied electric field.
- Molecular Structure and Dipole Moments: Molecules like water have a bent structure resulting in permanent dipole moments due to the uneven distribution of charges.
- Effect of Electric Field: An external electric field causes molecules with permanent dipole moments to align with the field, creating orientational polarization.
- Examples of Molecules: Water and nitrogen dioxide are examples of molecules with permanent dipole moments due to their structural characteristics.
- Torque on Dipole Moments: The applied electric field exerts a torque on the permanent dipole moments, leading to their alignment with the field.
Orientational polarization is the lining-up of molecules that already have a permanent dipole when an electric field is applied. An oxygen molecule does not do that. Each oxygen atom has 6 outer electrons. Two oxygen atoms share a double bond, the nuclei sit about 121 picometers apart, and both ends carry the same charge, so there is no permanent dipole. Hydrogen and nitrogen molecules are the same. A water molecule is different.
Water is bent. Oxygen bonds to two hydrogens. The oxygen end is slightly negative and the hydrogen ends are slightly positive, so two dipoles point from oxygen toward each hydrogen.
The angle between these two dipole moments is 105 degrees. The result is a permanent dipole moment in each water molecule, even without an external electric field. Molecules like nitrogen dioxide have similar permanent dipole moments for the same reason.
When an external electric field is applied, molecules with permanent dipole moments align themselves with the field. This happens because the electric field exerts a torque on the dipole moments. This alignment process is called orientational polarization.
