Question

Lanthanoid contraction occurs because:

• A. the 4f electrons, which are gradually added, create a strong shielding effect
• B. the 4f orbitals are greater in size than the 3d and 3f orbitals
• C. the 5f orbitals strongly penetrate into the 4f orbitals
• D. the poor shielding effect of 4f electrons is coupled with the increased attraction between the nucleus and the added electrons

Answer 1

The correct option is D the poor shielding effect of 4f electrons is coupled with the increased attraction between the nucleus and the added electrons

Lanthanoid contraction results from poor shielding of nuclear charge (nuclear attractive force on electrons) by 4f electrons. The 6s electrons are drawn towards the nucleus, thus resulting in a smaller atomic radius. Along with this addition of electrons in 4f subshell and increase in nuclear charge are also responsible.