(a) For cach of the three types of polarization, briefly describe the mechanism by which dipoles are induced and/or oriented by the action of an applied electric field. (b) For gaseous argon, solid LiF, liquid \(\mathrm{H}_{2} \mathrm{O}\) and solid Si, what kind(s) of polarization is (are) possible? Why?

Electronic polarization is a phenomenon that occurs when an external electric field is applied to a material, causing a slight displacement of the negatively charged electrons with respect to the positively charged nuclei. This shift creates an induced dipole moment within the atoms or molecules of the material.

Let's visualize how this happens. Imagine the nucleus of an atom as the sun, with the electrons orbiting like planets. When you introduce an electric field, it's like a wind pushing on the planets, causing them to shift slightly in their orbits. This displacement is what we call electronic polarization.

Electronic polarization can happen in all states of matter, be it gases like argon, solids like silicon, liquids like water, or even in ionic compounds such as lithium fluoride (LiF). It's a fundamental response and is generally small and quick, reverting immediately after the external electric field is removed.

In summary, electronic polarization is the universal answer of atoms to electric fields, where the cloud of electrons around a nucleus adjusts its position slightly, leading to an overall polarized material.

Ionic polarization comes into play in materials composed of positive and negative ions. This polarization occurs when an electric field is applied and the ions are displaced in opposite directions according to their charge. The result is a more substantial induced dipole in the material compared to electronic polarization.

Think of table salt (NaCl). It's made up of positively charged sodium ions and negatively charged chloride ions. When we apply an electric field, the sodium ions move slightly towards the negative side, and the chloride ions move towards the positive side, creating an induced dipole across each pair of ions.

While electronic polarization is relatively quick and reversible, ionic polarization involves the actual movement of bulkier ions and takes more time to establish and to reverse. Materials like LiF exhibit ionic polarization because of their ionic nature but do not display orientation polarization since they do not contain polar molecules with permanent dipole moments.

It is important to note that ionic polarization only happens in ionic compounds and significantly affects the dielectric properties of the material, such as the dielectric constant, which measures a material's ability to store electrical energy.

Orientation polarization is exclusive to substances with polar molecules; these are molecules having a permanent dipole moment. When an external electric field is applied, these permanent dipoles tend to align themselves with the field.

A classic example is water (H2O). Water molecules each have a slightly positive end (near the hydrogen atoms) and a slightly negative end (near the oxygen atom). Apply an electric field, and it's like a bunch of tiny magnets at a picnic on a windy day, all trying to align with the wind direction. Some will twist and turn but overall, they'll end up pointing more or less along the direction of the breeze.

Orientation polarization is dependent on the presence of a permanent dipole moment and the ability of the dipoles to reorient themselves; hence, it doesn't occur in non-polar substances like gaseous argon or in pure covalent solids like silicon. In liquid water, this type of polarization is very influential and leads to a high dielectric constant, making water an excellent medium for storing electric fields.

It's also temperature-dependent—warmer temperatures give molecules more energy to resist alignment, leading to lower polarization levels. When the electric field is removed, these polar molecules tend to return to their random orientations, albeit quite slowly compared to the instant de-polarization seen in electronic polarization.