d/f-block Contractions

Question 1

Explain the lanthanide contraction

Answer 1

Lanthanide contraction causes greater than expected decrease in atomic radii of the lanthanide series.

This is caused by poor shielding of nuclear charge by 4f electrons, therefore the 6s electrons are drawn towards the nucleus, thus resulting in a smaller atomic radius.

Question 2

Explain the d-block contraction (scandide contraction)

Answer 2

Elements with fill d10 subshell, example Gallium, will have d-block contraction, this is because:

• Poor shielding of the nuclear charge by the electrons in the d orbitals.
• This means that valence electrons are pulled in more and atomic radius is smaller than expected which leads to increase in ionization potentials as its harder to overcome that nuclear attraction between nucleus and outer valence electrons