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More number of oxidation states are exhibited by the actinoids than by the lanthanoids. The main reason for this is :-
A
More energy difference between 5f and 6d orbitals than that between 4f and 5d orbitals
B
Lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals
C
Greater metallic character of the lanthanoids than that of the corresponding actinoids
D
More active nature of the actinoids
Detailed Solution
Lanthanoids show mainly the +3 oxidation state, with +2 and +4 only in a few cases.
Actinoids show a much wider range of oxidation states, from +3 up to +7 (for example U shows +3, +4, +5, +6 and Np shows up to +7).
The reason is that in actinoids the 5f, 6d and 7s orbitals have comparable energies; the energy difference between 5f and 6d is very small.
So electrons from all three kinds of orbitals can take part in bonding.
In lanthanoids the energy gap between the 4f and 5d orbitals is larger, and the 4f electrons are deeply buried, so they are not easily available for bonding.
Hence the main reason is the lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals.
Actinoids show a much wider range of oxidation states, from +3 up to +7 (for example U shows +3, +4, +5, +6 and Np shows up to +7).
The reason is that in actinoids the 5f, 6d and 7s orbitals have comparable energies; the energy difference between 5f and 6d is very small.
So electrons from all three kinds of orbitals can take part in bonding.
In lanthanoids the energy gap between the 4f and 5d orbitals is larger, and the 4f electrons are deeply buried, so they are not easily available for bonding.
Hence the main reason is the lesser energy difference between 5f and 6d orbitals than between 4f and 5d orbitals.