Question

What is the effect of lanthanoid contraction in lanthanoid series of elements with increasing atomic number?

• A. Decreases in atomic radii
• B. Increases in atomic radii
• C. Decreases in melting point
• D. Increases in melting point

Answer 1

Answer: (A)

Lanthanide contraction is the steady decrease in size of atoms and ions of rare earth elements with increasing atomic number from lanthanum.
(Atomic number $=57$ )
It is caused by poor shielding effect of $4f$-electrons. In row $3$ , we have $4f$-electrons which do not shield good, causing a greater nuclear charge.
This greater nuclear charge has a greater pull on electrons.
Thus, we can say that decrease in atomic radii is the effect of lanthanoid contraction in lanthanoid series.