General Characteristics and Comparison of Actinoids with Lanthanoids
(i) Electronic configuration
- The general electronic configuration for actinoids is [Rn]86 5f1-14 6d0-1 7s2 and for lanthanoids is [Xe]54 4f0-14 5d0-1 6s2.
(ii) Atomic and lonic sizes
- Like lanthanoids the ionic radii of actinoids gradually decrease across the series due to the poor screening effect of nuclear charge exerted by the f electrons.
(iii) Oxidation states
- The lanthanoids exhibit +3 oxidation states. Some elements may exhibit + 2 and + 4 oxidation states due to extra stability of fully-filled and half-filled orbitals.
- On the other hand Actinoids also exhibit + 3 oxidation state. They also exhibit varying oxidation states due to the comparable energies of 5f, 6d, and 7s.
(iv) Chemical reactivity
- Earlier members of the lanthanide series are more reactive and are comparable to CSolution: They resemble Al with increasing atomic number.
- Finely divided Actinoids are highly reactive metals and when added to boiling water gives a mixture of oxide and hydride.
- At moderate temperatures Actinoids combine with most of the non-metallic elements.
- Actinoids remain unaffected by the action of alkalies but gets slightly affected by nitric acid due to the formation of a protective oxide layer.