Question

Lanthanoids contraction is due to increase in:

• A. shielding by $f$-electrons.
• B. atomic number.
• C. effective nuclear charge.
• D. size of $4f$-orbital.

Answer 1

The correct option is C effective nuclear charge.

The Lanthanide Contraction refers to the fact that the 5s and 5p orbitals penetrate the 4f sub-shell so the 4f orbital is not shielded from the increasing nuclear change, which causes the atomic radius of the atom to decrease. This decrease in size continues throughout the series.

As the proton number increases and the atomic radius decreases, the ionization energy increases. This is due to a more positively charged nucleus and a greater pull on the electrons by the nucleus. A greater pull is the result of an increased effective nuclear charge. Effective nuclear charge is caused by the nucleus having a more positive charge than the negative charge on the electron (net positive charge).

Lanthanoide contraction is due to increase in effective nuclear charge and the poor shielding of f orbital electrons.