Question

The size of the atoms from Lanthanum to Lutetium, shows a steady and slow decrease in atomic size.

1. Do you agree with it? 

2. What are the causes for this? 

3. What are the consequences of this phenomenon?

Answer 1

(1). Yes.

(2). It is due to Lanthanoid contraction. In Lanthanoid series the 4f electrons are being added in the antipenultimate shell. The 4f electrons have very poor shielding effect because of diffused shape of 4f orbitals and the effective nuclear charge experienced by each 4f electrons increases. Hence there is a regular decrease in radii with increase in atomic number.

3. Consequences of lanthanoid contraction are :

• Difficulty in separation of lanthanoids due to similarity in chemical properties.
• Similarity in size of elements belonging to same group of second & third transition series.