Identify all the correct statements for Lanthanide contraction. a) The covalent properties of the Lanthanide metal hydroxides increases from La to Lu. b) The chemical reactivity decreases from La to Lu. c) La(OH)3 is more basic than Lu(OH)3. d) Zr and Hf have about the same radius. e) Separation of Lanthanides from one another is easy,
(A) On moving from La to Lu, size of cation decreases due to poor shielding of f-orbitals. This contraction is called lanthanide contraction. As size of cation decreases, its polarizing power increases thus, covalent character or properties of lanthanoide metal hydroxides increases. (B) The first few lanthanoids are quite reactive like calcium but with increasing atomic number, their reactivity becomes similar to Al, i.e. reactivity decreases. This is because of lanthanoid contraction. The ionisation becomes difficult as size of atom decreases. Hence, chemical reactivity decreases from La to Lu. (C) From La to Lu, size of metal cation decreases, i.e. covalent character in metal hydroxides increases and basic strength decreases. Thus, La(OH3. can easily give OH−ions. Hence, La(OH)3 is more basic than Lu(OH)3. (D) On moving down the group from Zr to Hf, size of atom should increases. But due to lanthanoide contraction, Zr and Hf have almost same radius. This can explained on the basis of shielding effect. Due to presence of f-orbitals and their poor shielding, effective nuclear charge on the outer shell electron increases and as a result, size of Zr and Hf becomes equal. (E) Due to lanthanoid contraction, the ionic radii of lanthanoides decreases which also affect their chemistry. Thus, the separation of lanthanoides from one another is not easy.