what is fajan's rule?
how is related with the oxidation state and oxidising power?
explain with example
Thanks.
In an ionic molecule , the cation polarises the anion. If the cation has high polarising power , it attracts the electron charge cloud of the anion towards itself more strongly and this results in that the electron charge clouds of both the ions overlap together. Thsi overlap decreases the ionic character between cation and anion in a moleclue. Greater is the polarising power of a cation , greater will be the amount of covalent character produced in the ionic molecule.
Conditions for Fazan's rule is given below:
1) The cation should have high positive charge on it. Higher is the positive charge on the cation in a given ionic molecule , higher will be its polarising power and hence greater will be the magnitude of covalent character.
2) The cation should be small in size. Smaller is the cation in size , greater is its polarising power and hence greater is the amount of covalent character produced in the ionic molecule.
3) The cation should have ns2p6d10 configuration. d electrons present in 18 - electron cation has poorer sheilding of the nucleus than the s and p electrons present in 8 electron cation. Consequently, the 18 electron cation would have greater polarising power than the 8 electron cation.
If an element forms two chlorides, the chloride of the element with higher positive charge (high oxidation state) is covalent (as it has high polarising power) while that of the element with lower positive charge is ionic.
For eg.-
Tl+ = +1 , TlCl is ionic
Tl3+ = +3, TlCl3 is covalent
Similarly, SnCl2 = ionic
SnCl4 is covalent
Conditions for Fazan's rule is given below:
1) The cation should have high positive charge on it. Higher is the positive charge on the cation in a given ionic molecule , higher will be its polarising power and hence greater will be the magnitude of covalent character.
2) The cation should be small in size. Smaller is the cation in size , greater is its polarising power and hence greater is the amount of covalent character produced in the ionic molecule.
3) The cation should have ns2p6d10 configuration. d electrons present in 18 - electron cation has poorer sheilding of the nucleus than the s and p electrons present in 8 electron cation. Consequently, the 18 electron cation would have greater polarising power than the 8 electron cation.
If an element forms two chlorides, the chloride of the element with higher positive charge (high oxidation state) is covalent (as it has high polarising power) while that of the element with lower positive charge is ionic.
For eg.-
Tl+ = +1 , TlCl is ionic
Tl3+ = +3, TlCl3 is covalent
Similarly, SnCl2 = ionic
SnCl4 is covalent