Question

Which of the following factors may be regaded as the main cause of lanthanide contraction:

• A. Greater sheilding of $5d$ electron by $4f$ electrons
• B. Poorer sheilding of $5d$ electron by $4f$ electrons
• C. Effective sheilding of one $4f$ electron by another in the shell
• D. Pooer sheilding of one $4f$ electron by another in the shell

Answer 1

The correct option is D Pooer sheilding of one $4f$ electron by another in the shell

In lanthanides, there is poorer sheilding of $5d$ electrons by $4f$ electrons resulting greater attraction of the nucleus over $5d$ electrons and contraction of the atomic radii.