Discuss the consequences of lanthanide contraction
Answers
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*Consequences of Lanthanide Contraction:-
Following points will clearly depict the effect of lanthanide contraction:
1. Atomic size:
Size of the atom of third transition series is nearly the same as that of the atom of the second transition series. For example: radius of Zr = radius of Hf & radius of Nb = radius of Ta etc.
2. Difficulty in the separation of lanthanides:
As there is an only small change in the ionic radii of Lanthanides, their chemical properties are similar. This makes the separation of elements in the pure state difficult.
3. Effect on the basic strength of hydroxides:
As the size of lanthanides decreases from La to Lu, the covalent character of the hydroxides increases and hence their basic strength decreases. Thus, La (OH)3 is more basic and Lu(OH)3 is the least basic.
4. Complex formation:
Because of the smaller size but higher nuclear charge, tendency to form coordinate. Complexes increases from La3+ to Lu3+.
5. Electronegativity:
It increases from La to Lu.
6. Ionization energy:
Attraction of electrons by the nuclear charge is much higher and hence Ionization energy of 5d elements are much larger than 4d and 3d. In 5d series, all elements except Pt and Au have filled s-shell.
Elements from Hafnium to rhenium have same IE and after IE increases with the number of shared d-electrons such that Iridium and Gold have the maximum IE.