1. What is Polarization?
Polarization is the process of inducing a separation of positive and negative electrical charges within a system (like an atom, molecule, or dielectric material).
In an atom, the center of the negative electron cloud normally coincides with the positive nucleus. When an external electric field (E) is applied, the nucleus is pushed in the direction of the field, and the electrons are pulled in the opposite direction. This creates a dipole moment.
Where p is the induced dipole moment, q is the charge, and d is the distance of separation.
2. What is Polarizability?
Polarizability (α) is a measure of how easily the electron cloud of an atom or molecule can be distorted by an external electric field. It is a fundamental property of the species itself.
- High Polarizability: Large atoms (like Iodine) have electrons far from the nucleus that are held loosely, making them easy to polarize.
- Low Polarizability: Small atoms (like Fluorine) have electrons held tightly by the nucleus, making them difficult to polarize.
3. Relationship
The magnitude of the induced dipole moment is directly proportional to the strength of the external electric field. The proportionality constant is the polarizability.
4. Key Differences
| Feature | Polarization | Polarizability |
|---|---|---|
| Definition | The actual state of charge separation occurring. | The capacity or ease of becoming polarized. |
| Dependence | Depends on the strength of the external field. | An intrinsic property of the atom/molecule. |
| Unit | Coulomb-meter (C·m) | C·m²·V⁻¹ (or ų for polarizability volume) |
5. Factors Affecting Polarizability
Several factors influence how "distortable" a particle is:
- Atomic/Molecular Size: Larger species are generally more polarizable.
- Number of Electrons: More electrons usually lead to higher polarizability because there are more charges that can shift.
- Orientation: For non-spherical molecules, polarizability may differ depending on the direction of the electric field (anisotropy).
Related Topic Fajan's Rule