1. The document discusses Fajan's Rule, which states that the ability of a cation to polarize a nearby anion depends on factors like the cation's size, charge, and electronic configuration. This polarization leads to ionic compounds having some covalent character. 2. The factors that influence a cation's polarizing power and an anion's polarizability are discussed. Smaller cations and larger anions lead to greater polarization and more covalent character. 3. Several examples are given of how polarization affects the properties of ionic compounds, like their solubility, thermal stability, and melting points. Compounds with more covalent character through polarization have higher solubility in non-polar solvent

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Dr. Mohd Kamil Hussain
Department of Chemistry
Govt. Raza P.G. College Rampur, U.P. India
Fajan’s Rule & Its Applications
Lockdown
Covid-19

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Fajan’s Rule & Its Applications
Polarization:
When a cation approaches to an anion closely, it attracts the electron of anion and same time it
repels the positively charge nucleus of the anion, due to which electron charge density of the
anion no longer remain symmetrical, but is elongated towards the cation, Which is known as
distortion or polarization of anion by cation.
Dr. Mohd Kamil Hussain

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Polarizing Power and polariziblity
Dr. Mohd Kamil Hussain
The ability of cation to polarize a nearby anion is known as polarising power of cation, and the tendency of
anion to get polarized is known as polariziblity.
3. Electronic configuration of cation:
Hg+2 and Ca+2 size of the both cation is almost same, because of poor shielding of d-electrons; the anions electrons
get attracted more by the nucleus.
Hg+2 > Ca+2
1. Charge and size ( it increase with decrease in size of cation).
Be+2 > Mg+2 > Ca+2 > Sr+2 > Ba+2
2. Charge on cation ( it increase with increase in size of cation).
Na+ < Mg+2 < Al+3
Fe+2 < Fe+3
Sn+2 < Sn+4
Factor affecting polarizing power of anions:
It is clear from above equation polarizing power of cation depends upon

4. Dr. Mohd Kamil Hussain
1. Size of anion. Polarizibility of anions increases with increase the size of anions.
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As the negative charge increases the force of attraction between the nucleus of anion and its electron decrease due to which
polariziblity of anion increases .These factors are collectively called Fajans’s Rule.
Factor affecting polariziblity of anions:
2. Charge on anion: Polariziblity of anions increase with charge.
Results and properties affected by polarization or Applications of Fajans’s Rule.
1. Covalent nature of ionic compounds.
It is affected by polarization. If the extent of polarization is small then the bonds remain ionic, if extent of polarization is large,
covalent character becomes high.
According to this concept order of covalent character in following compounds is as
BeCl2 > MgCl2 > CaCl2
SnCl4 > SnCl2
HgCl2 > CaCl2
LiCl > NaCl > KCl > RbCl > CsCl

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2. Solubilty of compounds in non polar solvents.
As covalent nature increases solubility in non polar solvent increases.
LiCl > NaCl > KCl > RbCl > CsCl
3. Thermal stability of carbonates.
It decrease with increase in polarizing power power.
BeCO3 < MgCO3 < CaCO3 < SrCO3 < BaCO3
4. Melting point of ionic compounds:
Melting point of ionic compounds depends upon intermolecular forces of attraction which can be determined by either by lattice
energy concept or concept of polarization.
Melting points of ionic compounds decrease with increase in Polarisation or Covalent nature.
BeCl2 < MgCl2 < CaCl2 < SrCl2 < BaCl2

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Conclusions:
For more ionic nature. Cation size should be large and size of anion should be small.
For more covalent nature. Cation size should be small and size of anion should be large.
For high polarizing power size of cation should be small.
For high polariziblity size of anion should be large.
For high melting points of ionic compounds size of cation should be large and anion should
be small.

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1. Why Cu2O is more covalent then Na2O?
2. Why LiCl is covalent in nature.
3. Which has highest melting point and why? MgSO4 , CaSO4, BaSO4
4. Which has lowest melting point and why? MgSO4 , CaSO4, BaSO4
5. How will you determine the covalent and ionic characters of electrovalent compounds?
6. Which is more covalent? BeCl2 or LiCl.
7. Mention the factors which affect the polarization and polariziblity.
8. Which is more covalent SnCl2 or SnCl4?
9. Which is more covalent FeCl2 or FeCl3?
Assignment