(i) Electronic configuration:
The general electronic configuration for lanthanoids is [Xe] 0-14 5d 0-1 6s2 and that of actinoids is [Rn] 5f 0-14 6d0-1 7s2. Unlike 4f orbitals, 5 f orbitals are not deeply buried and participate in bonding to a greater extent.
(ii) Atomic and ionic size:
Similar to lanthanoids, actinoids also exhibit actinoid contraction over all decrease in atomic and ionic radii. The contraction is greater due to the poor shielding effect of 5f orbitals. Hence there is an unexpected in the atomic and ionic sizes of actionoids. ‘
(iii) Oxidation states:
The principal oxidation states 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.
(iv) Chemical activity:
In the lanthanoide 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).
