Question

 Explain 

(a) Why is La(OH)₃ stronger base than Lu(OH)₃? 

(b)There is a greater range of oxidation states among the actinoids than among the lanthanoids. 

(c) Actinoid contraction is greater from element to element than lanthanoid contraction. Why? 

Answer 1

(a) Due to lanthanoid contraction, the size of Lu³⁺ is smaller than that of La³⁺ ion. Thus, Lu-OH bond is stronger than La-OH bond. Hence, La(OH)₃ is stronger base than Lu(OH)₃. 

(b) This is due to comparable energies of 5f,6d and 7s orbital in actinoids 

(c) This is due to poor shielding effect by 5f electrons in actinoid as compared to that by 4f electron in the lanthanoids.