Polarization meaning-Ionic potential-polarizability and polarizing power.

Polarization meaning in chemistry

Polarization in chemistry means deformation of symmetric electron charge cloud of anion by cation.

In case of ionic crystal , it has been observed that, the positive electric field of cation pull the electronic sphere of an anion from their equal distance.

But the positive electric field of cation repulse the nucleus of anion .

As a result, the deformation of symmetric electron charge cloud of anion by cation is called polarization of anion.

Generally, cation with smaller size or with high positive charge cause the high polarization of anion.

On the other hand, anion with large size or with high negative charge also cause the high polarization of itself.

For example, Al3+ ion cause the high polarization of a particular anion than Na+ ion ,due to small size and high charge with respect to Na+ ion.

What is polarizing power of cation ?

The polarizing power of cation is defined as the capability to distort the electron charge cloud of an anion.

Now, it has been experimentally found that, cation with smaller size or with high positive charge have its high polarizing power.

For example, Al3+ ion have more polarizing power than Na+ ion, due to small size and high charge of Al3+ with respect to Na+ ion.

What is polarizability of anion in chemistry

Polarizability is defined as the property of an anion to become polarized through the deformation of electron charge cloud by cation.

Polarizability of an anion increase with increase in anionic size or anionic charge.

For example, the polarizability of I– anion is higher than F — ion, due to large size of iodide ion.

If the polarizability of an anion increase, then covalent character of the concern compound increase. Such as , AgI is more covalent than AgF .

Ionic potential(ф) definition in chemistry

A parameter is used to expressed the polarizing power of cation is known as ionic potential . It is denoted by the symbol ‘ф’ .

The ionic potential is defined as the ratio of cationic charge and cationic radius.

With increasing the value of ‘ф’ , the polarizing power of cation increases. As a result, the covalent character in ionic compounds increases.

Periodic variation of covalent character in ionic compounds .

( I )When we move from left to right along a period, the cationic charge increases and hence cationic radius decreases .

That is, the value of ‘ф’ increases .Consequently, the covalent nature in ionic compounds increases .

For example, the value of ionic potential (‘ф’) for Na, Mg, Al increase from Na to Al . Hence, covalent character of the their relating compound increases in the same order.

( II ) On the other hand , if we moved from top to bottom along a group , the cationic charge remain unchanged, but due to increase of ionic radius, the value of ‘ф’ decreases.

Consequently, the covalent nature in ionic compounds increases .

For example, the order of ionic potential (‘ф’) value of group-II elements, such as Be , Mg and Ca are decrease from top to bottom.

Hence covalent character of their concerned compounds slowly decrease from top to bottom , that is from Be to Mg to Ca. Same explanation for Li , Na and K metal .

(III ) In case of different oxidation state of same metal, the value of ‘ф’ increase with increase in oxidation number .

Consequently, the covalent character with higher oxidation state increases.

For example, the value of ‘ф’ of Sn4+ ion is greater than Sn2+ ion, hence SnCl4 is more covalent than SnCl2 . Same explanation for Fe.