Question

Explain actinoid contraction. f- block

Answer 1

Actinoids:

• Actinides are elements starting from atomic numbers from 89(Actinium) to 103(Lawrencium).
• They include naturally occurring elements of thorium, protactinium, and uranium and eleven transuranic i.e., artificially produced by nuclear reactions.
• They are highly electropositive, the common oxidation state of actinides is +3.
• Actnoids are highly dense metals and form alloys with other metals.

Electronic configuration: [Rn] 5f^1-14 6d^0-1 7s²

Actinoid contraction:

• The atomic radii of actinoids decrease steadily from Thorium to Lawrencium due to increasing nuclear charge.
• From the Thorium filling of 5f-subshell starts. So, due to the weak shielding effect of the f-subshell, the nuclear charge increases, and the contraction in the size of atoms takes place.
• The size contraction in actinoids is greater as compared to that in lanthanoids.

Thus, due to the poor shielding effect of f- orbital actinoids undergo contractions called actinoids contraction.