Answer:
(i) Electronic configuration
Lanthanoids involve filling of 4f subshell while actinoids involve filling of 5f-subshell.
General electronic configuration of
Lanthanoids [Xe] 4f1-14 5d0–1 6s2
Actinoids [Rn] 5f1-14 6d0-1 7s2
(ii) Atomic and ionic sizes
(a)The atomic radii and ionic radii of tripositive lanthanoid ions (M3+) show a steady and gradual decrease in moving fromLa to Lu. Ionic radii decreases steadily from La to Lu. The Steady decrease in the sizeof lanthanoid ions (M3+) with the increase in atomic number is called lanthanoid contraction.
(b) The size of atom/cation decreases regularly along the actinoid series, the steady decrease in ionic radii with increase in atomic number is referred to as actinoid contraction. This is due to the poor shielding of 5f electrons.
(iii) Oxidation states
(a) All the lanthanoids exhibit a common stable oxidation state of +3. In addition some lanthanoids also show oxidation states of +2 and +4. These additional oxidation states are generally shown by those elements which by doing so attain the stable f°,f7or f14 configuration.
Ce4+ : [Xe] 4f0 and Tb4+ : [Xe] 4f7
Europium and ytterbium attains f7 and f14 configuration respectively when they attain +2 oxidation state.
Eu2+ : [Xe] 4f7 and Yb2+ : [Xe] 4f14
(b) The common oxidation states of actinoids is +3. Besides +3 oxidation state, actinoids such as Th, Pa, U, Np, Pu, Am, Cm and Bk also show an oxidation state +4. Some actinoids (U, Np, Pu and Am) also show an oxidation state of +6.
(iv) Chemical reactivity
(a) Lanthanoids arc highly electropositive in nature and they have almost similar chemical reactivity.
(b) All the actinoid metals are highly electropositive and as such they act as strong reducing agent. They are more reactive than lanthanoids.
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