Lanthanide contraction – causes and consequences

1. Lanthanide contraction :

” the steady decrease in the atomic and ionic radii of lanthanides with increasing the atomic number  is called Lanthanide contraction”.

Atomic radii do show some irregularities   but ionic radii decrease steadily  from La to Lu.

Causes :

When we proceed from one element to the next element in Lanthanide series, the additional electron enters the 4f  subshell.

When atomic number increases, the effective nuclear charge is increased by one Unit in  each step and no comparable increase in the mutual shielding effect of 4f electrons occur. It causes a contraction in the size of 4f subshell. Consequently,  atomic radii decreases with increasing the atomic number in 4f  series .

Consequences of Lanthanide Contraction:

1. Similarity in properties of lanthanides
   Since all lanthanides exhibit very similar chemical propertie, the process of separation is more difficult.

2. Difficulty in separation of lanthanides                                                              Due to similar ionic sizes of lanthanides, the process of separation is much more complex.

3. Decrease in basicity of lanthanide hydroxides
   Basic strength of lanthanides decreases from La(OH)₃ to Lu(OH)₃.

4. Similarity between 4d and 5d transition elements
   Due to lanthanide contraction, elements like Zr and Hf show nearly identical properties.