How would you account for the following : (i) Among lanthanoids , Ln(III) compounds are predominant , However, occasionally in solutions or in solid compounds, +2 and +4 ions are also obtained . (ii) The E_(M2+//M)^(@)for copper is positive (0.34V ) . Copper is the only metal in the first series of transition elements showing this behaviour . (iii) The metallic radii of the third (5d) series of transition metals are nearly the same as those of the corresponding members of the second series .

How would you account for the following : (i) Among lanthanoids , Ln(

1.	How would you account for the following : (i) Among lanthanoids , Ln(III) compounds are predominant , However, occasionally in solutions or in solid compounds, +2 and +4 ions are also obtained . (ii) The E_(M2+//M)^(@)for copper is positive (0.34V ) . Copper is the only metal in the first series of transition elements showing this behaviour . (iii) The metallic radii of the third (5d) series of transition metals are nearly the same as those of the corresponding members of the second series .
Answer» Solution :Lanthanoid metals show +2 and +4 oxidation states in solution or in SOLID compounds to ATTAIN extra stable `f^0` and `f^7` and `f^(14)`configurations. For EXAMPLE, EU and `Y_b` exhibit +2 oxidation states due to extra stability of half-filled and completely filled 4f-subshell respectively. CE and Tb exhibit + 4 oxidation states due to the extra stability of empty and half-filled 4f-subshell respectively.