According to fajan's rules neccessary conditions to form covalent bond is
Answers
Fajan's rules were developed based on the concept: "greater the polarization, greater is the covalent nature". There are two factors which are crucial in deciding the extent of polarization i.e.,
i) Polarizing power of cation: It is directly proportional to the charge density, which in turn is directly related to the charge and inversely related to the size; and
ii) The polarizability of an anion: It is the tendency to undergo polarization and is directly related to size as well as the negative charge. Larger anions are distorted easily.
We can easily conclude that greater the polarizing power of cation and greater the polarizability of anion, greater is the polarization and hence greater will be the covalent nature.
Thus,
1) Smaller the cation, greater is the covalent nature. i.e., Larger the cation greater is the ionic nature.
2) Larger the anion, greater is the covalent nature. i.e., Smaller the anion greater is the ionic nature.
It is also observed that the nuclear attraction is not properly shielded in transition metal ions which are also smaller in size. The cumulative effect is higher polarizing power and more covalent nature of compounds containing these ions, most of which have 18 electrons in their outer shell i.e. pseudo inert gas configuration.