Fajan's Rule
Kazimierz Fajans in 1923, gave some important points to predict whether a chemical bond is expected to be predominantly ionic or covalent.They are given below-
1. Size of Cations
2. Size of Anions
3. Charge on ions (Cations and Anions)
4. 18 electron configuration
1. Size of Cations
Smaller the size of cation, greater the covalent character.
A smaller cation has a higher polarizing power which distort more effectively the electron cloud of an anion. Therefore, smaller cations favor the covalent character.
Example: LiCl, NaCl, KCl, RbCl, CsCl
LiCl is most covalent among the given IA chlorides as the size of Li+ is smaller than that of other IA cations.
The order of covalent character is-
LiCl > NaCl > KCl > RbCl > CsCl
2. Size of Anions
Larger the size of anions, greater the covalent character.
A larger anion has a higher polarizability which means its electron cloud is more easily distorted. Therefore, larger anions favor covalent character.
Example: LiF, LiCl, LiBr, LiI
LiI is most covalent among the given IA halides as the sixe of iodide ion is larges.
So, the order of covalent character is-
LiI > LiBr > LiCl > LiF
3. Charge on ions (Cations and Anions)
Higher the charge on ions, greater the covalent character.
Higher charges on either the cation or the anion increase polarization.
Therefore, higher charges favor covalent character.
Example: NaCl, MgCl2, AlCl3
AlCl3 is most covalent among the given molecules as the chage on Al is +3 highest (charge on Na is +1 and on Mg is +2).
So, the order of covalent character is-
AlCl3 > MgCl2 > NaCl
4. 18 electron configuration
Molecules which follows 18 electron configuration is more covalent in nature than those molecules which follows 8 electron configuration.
Example: NaCl and CuCl
CuCl is more covalent as it follows 18 electron configuration while NaCl is more ionic because it follows 8 electron configuration.
Fajan's Rule MCQs
15 MCQs with Answer
Your Test Result
You answered out of questions correctly.
You got % marks.
