Question

Compare the chemistry of actinoids with that of the lanthanoids with special reference to:
(i) electronic configuration (iii) oxidation state
(ii) atomic and ionic sizes and (iv) chemical reactivity.

Answer 1

(i) Electronic configuration
The general electronic configuration for lanthanoids is [Xe]⁵⁴ 4f0-¹⁴ 5d^0-1 6s² and that for actinoids is [Rn]⁸⁶ 5f^1-14 6d^0-1 7s². Unlike 4f orbitals, 5f orbitals are not deeply buried and participate in bonding to a greater extent.
(ii) Oxidation states
The principal oxidation state of lanthanoids is (+3). However, sometimes we also encounter oxidation states of + 2 and + 4. This is because of extra stability of fully-filled and half-filled orbitals. Actinoids exhibit a greater range of oxidation states. This is because the 5f, 6d, and 7s levels are of comparable energies. Again, (+3) is the principal oxidation state for actinoids. Actinoids such as lanthanoids have more compounds in +3 state than in +4 state.
(iii) Atomic and lonic sizes
Similar to lanthanoids, actinoids also exhibit actinoid contraction (overall decrease in atomic and ionic radii). The contraction is greater due to the poor shielding effect of 5f orbitals.
iv. Chemical reactivity
In the lanthanide series, the earlier members of the series are more reactive. They have reactivity that is comparable to Ca. With an increase in the atomic number, the lanthanides start behaving similar to Al. Actinoids, on the other hand, are highly reactive metals, especially when they are finely divided. When they are added to boiling water, they give a mixture of oxide and hydride. Actinoids combine with most of the non-metals at moderate temperatures. Alkalies have no action on these actinoids. In case of acids, they are slightly affected by nitric acid (because of the formation of a protective oxide layer).

Answer 2

Properties	Lanthanoids	Actinides
Electronic  configuration	[Xe] 4f1‐14, 5d0‐1 ,6s2	[Rn] 5f1‐14, 6d0‐1 ,7s2.
Atomic/ionic sizes	Size decreases from La to Lu,  and size is more than actinides.	Size decreases from Ac to Lw, and  size is smaller than lanthanoids due  to poorer shielding of 5f electrons
Oxidation  states	Common oxidation is +3 where  other oxidation states are +2,  +4.It is due to a large energy gap  between 4f, 5d and 6s subshell	Common oxidation is +3 where  other oxidation states are +2, +4,+5  and+7 due to due to small energy  difference between 5f, 6d and 7s  orbitals
Chemical  reactivity	The earlier member quite  reactive but with increasing  atomic number they behave like aluminum.	The actinides highly reactive  ,especially in finely divided.
Complex  formation	Less tendency to form complex due to less charge density.	More tendency to form complex due to high charge density.