Explain dipole-dipole forces and their characteristics.

(N/A) Dipole-dipole forces act between molecules possessing a permanent dipole. For example,$HCl$,$HF$,$CO$,$NO$,and $NH_{3}$ exhibit dipole-dipole forces.
Ends of the dipoles possess partial charges,denoted by the Greek letter delta $(\delta)$. These partial charges are always less than the unit electronic charge $(1.6 \times 10^{-19} \ C)$.
Formation of dipole-dipole forces: Neighbouring polar molecules interact with each other. Figure $(a)$ shows the electron cloud distribution in a hydrogen chloride dipole,and Figure $(b)$ shows the dipole-dipole interaction between two $HCl$ molecules.
Characteristics:
- This interaction is stronger than London dispersion forces but weaker than ion-ion interaction because only partial charges are involved.
- The attractive force decreases as the distance between the dipoles increases.
- The interaction energy is inversely proportional to the distance between polar molecules.
- Dipole-dipole interaction energy between stationary polar molecules (as in solids) is proportional to $1/r^{3}$,and that between rotating polar molecules is proportional to $1/r^{6}$,where $r$ is the distance between the polar molecules.