Lanthanoids and lanthanoid contraction
- The pair of lanthanoid ions which are diamagnetic is Answer: 2. Ce⁴⁺ and Yb²⁺ Key idea: diamagnetic means no unpaired electrons, so 4f⁰ or 4f¹⁴ . mathrmCe⁴⁺ : 4f⁰ ; mathrmYb²⁺ : 4f¹⁴ . Both dia... 1
- Gadolinium has a low value of third ionisation enthalpy because of Answer: 3. high exchange enthalpy Key idea: exchange enthalpy stabilises half-filled subshells. Gd is [Xe]4f⁷5d¹6s² . Removing the third ele... 1
- The incorrect statement among the following is : Answer: 2. Most of the trivalent Lanthanoid ions are colorless in the solid state. Key idea: compare f-block properties. Actinoid contractio... 1
- Zr (Z=40) and Hf (Z=72) have similar atomic and ionic radii because of : Answer: 3. lanthanoid contraction Key idea: lanthanoid contraction. Between Zr (4d) and Hf (5d) come the 14 lanthanoids, whose poor shieldin... 1
- Which one of the following statements related to lanthanons is incorrect? Answer: 2. All the lanthanons are much more reactive than aluminium. Key idea: check each statement against NCERT facts on lanthanoids. Stat... 1
- The electronic configurations of Eu (Atomic No. 63), Gd (Atomic No. 64) and Tb (Atomic No. 65) are : Answer: 4. [Xe]4f⁷6s² , [Xe]4f⁷5d¹6s² and [Xe]4f⁹6s² Key idea: half-filled 4f⁷ is extra stable, and Gd and Tb follow from it. Eu (63): [Xe]4... 1