As the polarisation power increases the distortion of the electron cloud of the anion increases. Starting from a 100% ionic model, the distortion of the anion’s electrons brings them closer to the cation, and increases the electron density between the two atoms. The bond becomes more covalent as it more resembles the electrons being shared than separate ions.

On increasing solubility size of molecule increases so polarisation increases

Introduction:
Covalent character refers to the degree of sharing of electrons between two atoms in a chemical bond. It is influenced by several factors, including the nature of the atoms involved, electronegativity, and the size of the ions. The polarization power of a cation is another important factor that affects the covalent character of a compound.

Explanation:

1. Definition of polarization power:
The polarization power of a cation refers to its ability to distort the electron cloud of an anion towards itself. It is directly related to the charge and size of the cation. Cations with higher charge and smaller size have greater polarization power.

2. Effect on anion:
When a cation with high polarization power approaches an anion, it exerts a stronger electrostatic force on the anion's electron cloud. This force leads to the displacement of electron density towards the cation, causing the anion to become polarized.

3. Formation of a polar covalent bond:
The polarization of the anion's electron cloud induces a partial positive charge on the cation and a partial negative charge on the anion. This charge separation results in an electrostatic attraction between the two ions, similar to an ionic bond. However, since the electron cloud is shared to some extent, a covalent character is introduced.

4. Increasing covalent character:
As the polarization power of the cation increases, the electron cloud of the anion is more strongly attracted towards the cation. This leads to a greater displacement of electron density and a higher degree of charge separation between the ions. Consequently, the covalent character of the bond increases.

5. Factors influencing polarization power:
The polarization power of a cation depends on its charge and size. Cations with higher charges have more positive charge density and can attract the electron cloud more strongly. Similarly, smaller cations have a higher charge density due to their smaller size, which enhances their polarization power.

6. Examples:
For example, consider the compounds LiF and CsF. Lithium (Li) is a smaller cation with a +1 charge, while cesium (Cs) is a larger cation with a +1 charge. Due to its smaller size and higher charge density, Li has a higher polarization power compared to Cs. Consequently, LiF has a higher covalent character due to the stronger polarization of the F- ion.

Conclusion:
In summary, the covalent character of a compound increases when the polarization power of the cation increases. This is because the cation with higher polarization power can distort the electron cloud of the anion more effectively, leading to a greater degree of charge separation and sharing of electrons between the ions.