# Step-by-Step Solution and Explanation Let's answer each question as a helpful tutor would, providing clear explanations and final answers. --- ### 1. **Lanthanide Oxidation States Beyond 3+** **Step-by-step explanation:** - **Electronic Structure:** Lanthanides generally have the configuration [Xe]4fⁿ6s². The 4f, 5d, and 6s electrons can participate in bonding. - **3+ State:** Most common because removing three electrons (two 6s and one 4f/5d) is energetically favorable. - **2+ States:** Some lanthanides (e.g., Eu, Yb, Sm) form stable 2+ ions when the 4f shell is half-filled (Eu²⁺, 4f⁷) or completely filled (Yb²⁺, 4f¹⁴), which are particularly stable configurations. - **4+ States:** Ce, Pr, Tb can form 4+ ions due to the relatively lower energy required to remove an additional electron to achieve a stable empty, half-filled, or filled subshell. - **Stability:** Stability of these oxidation states is enhanced when the resulting electron configuration is particularly stable (empty, half-filled, or fully filled f subshells). **Final Answer:** Lanthanides form stable oxidation states other than 3+ when the resulting electron configuration achieves extra stability (e.g., empty, half-filled, or filled 4f subshells). For example, Eu²⁺ (4f⁷) and Yb²⁺ (4f¹⁴) are stable due to half/full-filled 4f orbitals. --- ### 2. (a) **Origin of Magnetism in Lanthanides** **Explanation:** - Magnetism arises due to unpaired electrons in the 4f orbitals. - The 4f electrons are well shielded from the external environment, so their magnetic moments are largely unquenched. - The total magnetic moment is a combination of spin and orbital contributions. **Final Answer:** The magnetism in lanthanides arises from unpaired 4f electrons, whose magnetic moments are not significantly affected by the external environment due to shielding by outer electrons. --- (b) **Oxidation States in Lanthanides** **Explanation:** - The most common oxidation state is +3. - Some also exhibit +2 (e.g., Eu, Yb, Sm) and +4 (e.g., Ce, Tb) states, due to particularly stable electronic arrangements. **Final Answer:** Lanthanides predominantly show the +3 oxidation state. Some can also exhibit +2 or +4 states when these lead to particularly stable electronic configurations. --- ### 3. **Cation Exchange Order: Pb²⁺, Ni²⁺, Sr²⁺, Co²⁺, H⁺** **Explanation:** In cation exchange columns, ions are retained based on increasing affinity (selectivity series: H⁺ < Na⁺ < Sr²⁺ < Pb²⁺ < Co²⁺ < Ni²⁺). Least retained ions come out first. **Order of elution:** H⁺ → Sr²⁺ → Pb²⁺ → Co²⁺ → Ni²⁺ **Final Answer:** The order in which cations come out is: **H⁺, Sr²⁺, Pb²⁺, Co²⁺, Ni²⁺** (assuming typical cation-exchange resin). --- ### 4. **Extraction of Uranium (First Process)** **Brief Steps:** 1. **Mining & Crushing:** Uranium ore is mined and crushed. 2. **Leaching:** Treated with acid (H₂SO₄) or alkali to dissolve uranium as UO₂²⁺. 3. **Purification:** Solution filtered, impurities removed by solvent extraction/ion exchange. 4. **Precipitation:** Uranium is precipitated as ammonium diuranate. 5. **Conversion:** Heated to produce U₃O₈ or UO₂. **Final Answer:** Uranium extraction involves crushing the ore, acid/alkali leaching, purification, precipitation as ammonium diuranate, and conversion to uranium oxide. --- ### 5. **Uses of Thorium** - Nuclear fuel (in breeder reactors) - Alloying agent in magnesium - Mantles for gas lamps - High-quality lenses (thorium oxide glass) - Catalyst in chemical reactions **Final Answer:** Thorium is used as nuclear fuel, in gas lamp mantles, alloying, high-quality lenses, and as a catalyst. --- ### 6. **Stability of f-Orbitals** **Explanation:** - Empty, half-filled, and fully-filled f-orbitals have extra stability due to exchange energy and symmetry. - Examples: Eu²⁺ (4f⁷), Yb²⁺ (4f¹⁴). **Final Answer:** Empty, half-filled, and fully-filled f-orbitals are stable due to exchange energy and symmetrical arrangements. --- ### 7. **Why Lanthanide Contraction Occurs** **Explanation:** - Poor shielding by 4f electrons. - Increased nuclear charge across the series pulls electrons closer. - Result: gradual decrease in ionic radius (lanthanide contraction). **Final Answer:** Lanthanide contraction occurs due to poor shielding by 4f electrons, causing greater nuclear attraction and smaller atomic/ionic radii across the series. --- ### 8. (a) **Why Complexes Appear Colourful** **Explanation:** - d-d transitions: Absorption of visible light excites electrons between d-orbitals of different energies. - Examples: [Ti(H₂O)₆]³⁺ (purple), [Ni(H₂O)₆]²⁺ (green). **Final Answer:** Complexes appear colorful due to d-d electronic transitions which absorb certain wavelengths of visible light, giving the complex its color. --- (b) **Are Actinides More Colourful Than Lanthanides?** **Explanation:** - Actinides have more variable oxidation states and more partly filled f-orbitals, leading to more color. **Final Answer:** Yes, actinides are generally more colorful than lanthanides due to variable oxidation states and electronic transitions. --- (c) **Complex Stability: Actinides vs Lanthanides** **Explanation:** - Actinides often form more stable complexes due to larger size and higher charge density. **Final Answer:** Actinides form more stable complexes than lanthanides due to higher charge density and variable oxidation states. --- ### 9. (a) **Similarities: Lanthanides and Actinides** - Both have f-block elements. - Show +3 oxidation state. - Exhibit lanthanide/actinide contraction. - Similar chemical reactivity. - Form complexes. --- (b) **Distinguish Between Lanthanides and Actinides** - Lanthanides: 4f-block, mostly stable, less radioactive. - Actinides: 5f-block, many are radioactive, more variable oxidation states. --- ### 10. **Reduction of Thorium Oxides to Metal** **Methods:** 1. **Calcium reduction** 2. **Aluminium reduction (aluminothermic)** 3. **Electrolytic reduction** 4. **Magnesium reduction** --- ### 11. **Preparation Reactions** (i) **LaBr₃:** La + 3Br₂ → 2LaBr₃ (ii) **La₂(SO₄)₃.3Na₂SO₄.8H₂O:** Mix La₂(SO₄)₃ with Na₂SO₄ in water, crystallize. (iii) **La₂(CO₃)₃:** La(NO₃)₃ + Na₂CO₃ → La₂(CO₃)₃ + NaNO₃ --- ### 12. **Consequences of Lanthanide Contraction** - Decrease in ionic/atomic radii. - Similarities in properties of post-lanthanide elements. - Difficulty in separation of lanthanides. - Increased density and hardness. --- ### 13. **Synthesis of Pu-239** **Steps:** 1. \( ^{238}U + n \rightarrow ^{239}U \) 2. \( ^{239}U \xrightarrow{\beta^-} ^{239}Np \) 3. \( ^{239}Np \xrightarrow{\beta^-} ^{239}Pu \) --- ### 14. **Uses of Plutonium** - Nuclear fuel (Pu-239 in reactors) - Nuclear weapons - Power source in space probes (radioisotope thermoelectric generators) - Research in nuclear chemistry --- If you need a detailed explanation or step-by-step answer to any specific question, let me know!

The solution provides clear answers to each question regarding lanthanides and actinides, covering topics such as oxidation states, magnetism, extraction processes, and uses of thorium and plutonium. Key concepts include the stability of f-orbitals, lanthanide contraction, and the colorful nature of complexes due to electronic transitions. Each section is structured for clarity and understanding.

# Step-by-Step Solution and Explanation Let's answer each question as a helpful tutor would, providing clear explanations and final answers. --- ### 1. **Lanthanide Oxidation States Beyond 3+** **Step-by-step explanation:** - **Electronic Structure:** Lanthanides generally have the configuration [Xe]4f^n6s^2. The 4f, 5d, and 6s electrons can participate in bonding. - **3+ State:** Most common because removing three electrons (two 6s and one 4f/5d) is energetically favorable. - **2+ States:** Some lanthanides (e.g., Eu, Yb, Sm) form stable 2+ ions when the 4f shell is half-filled (Eu^2+, 4f^7) or completely filled (Yb^2+, 4f^14), which are particularly stable configurations. - **4+ States:** Ce, Pr, and Tb can form 4+ ions due to the relatively lower energy required to remove an additional electron to achieve a stable empty, half-filled, or filled subshell. - **Stability:** Stability of these oxidation states is enhanced when the resulting electron configuration is particularly stable (empty, half-filled, or fully filled f subshells). **Final Answer:** Lanthanides form stable oxidation states other than 3+ when the resulting electron configuration achieves extra stability (e.g., empty, half-filled, or filled 4f subshells). For example, Eu^2+ (4f^7) and Yb^2+ (4f^14) are stable due to half/full-filled 4f orbitals. --- ### 2. (a) **Origin of Magnetism in Lanthanides** **Explanation:** - Magnetism arises due to unpaired electrons in the 4f orbitals. - The 4f electrons are well shielded from the external environment, so their magnetic moments are largely unquenched. - The total magnetic moment is a combination of spin and orbital contributions. **Final Answer:** The magnetism in lanthanides arises from unpaired 4f electrons, whose magnetic moments are not significantly affected by the external environment due to shielding by outer electrons. --- (b) **Oxidation States in Lanthanides** **Explanation:** - The most common oxidation state is +3. - Some also exhibit +2 (e.g., Eu, Yb, Sm) and +4 (e.g., Ce, Tb) states, due to particularly stable electronic arrangements. **Final Answer:** Lanthanides predominantly show the +3 oxidation state. Some can also exhibit +2 or +4 states when these lead to particularly stable electronic configurations. --- ### 3. **Cation Exchange Order: Pb^2+, Ni^2+, Sr^2+, Co^2+, H^+** **Explanation:** In cation exchange columns, ions are retained based on increasing affinity (selectivity series: H^+ < Na^+ < Sr^2+ < Pb^2+ < Co^2+ < Ni^2+). Least retained ions come out first. **Order of elution:** H^+ → Sr^2+ → Pb^2+ → Co^2+ → Ni^2+ **Final Answer:** The order in which cations come out is: **H^+, Sr^2+, Pb^2+, Co^2+, Ni^2+** (assuming typical cation-exchange resin). --- ### 4. **Extraction of Uranium (First Process)** **Brief Steps:** 1. **Mining & Crushing:** Uranium ore is mined and crushed. 2. **Leaching:** Treated with acid (H2SO4) or alkali to dissolve uranium as UO2^2+. 3. **Purification:** Solution filtered, impurities removed by solvent extraction/ion exchange. 4. **Precipitation:** Uranium is precipitated as ammonium diuranate. 5. **Conversion:** Heated to produce U3O8 or UO2. **Final Answer:** Uranium extraction involves crushing the ore, acid/alkali leaching, purification, precipitation as ammonium diuranate, and conversion to uranium oxide. --- ### 5. **Uses of Thorium** - Nuclear fuel (in breeder reactors) - Alloying agent in magnesium - Mantles for gas lamps - High-quality lenses (thorium oxide glass) - Catalyst in chemical reactions **Final Answer:** Thorium is used as nuclear fuel, in gas lamp mantles, alloying, high-quality lenses, and as a catalyst. --- ### 6. **Stability of f-Orbitals** **Explanation:** - Empty, half-filled, and fully-filled f-orbitals have extra stability due to exchange energy and symmetry. - Examples: Eu^2+ (4f^7), Yb^2+ (4f^14). **Final Answer:** Empty, half-filled, and fully-filled f-orbitals are stable due to exchange energy and symmetrical arrangements. --- ### 7. **Why Lanthanide Contraction Occurs** **Explanation:** - Poor shielding by 4f electrons. - Increased nuclear charge across the series pulls electrons closer. - Result: gradual decrease in ionic radius (lanthanide contraction). **Final Answer:** Lanthanide contraction occurs due to poor shielding by 4f electrons, causing greater nuclear attraction and smaller atomic/ionic radii across the series. --- ### 8. (a) **Why Complexes Appear Colourful** **Explanation:** - d-d transitions: Absorption of visible light excites electrons between d-orbitals of different energies. - Examples: [Ti(H2O)6]^3+ (purple), [Ni(H2O)6]^2+ (green). **Final Answer:** Complexes appear colorful due to d-d electronic transitions which absorb certain wavelengths of visible light, giving the complex its color. --- (b) **Are Actinides More Colourful Than Lanthanides?** **Explanation:** - Actinides have more variable oxidation states and more partly filled f-orbitals, leading to more color. **Final Answer:** Yes, actinides are generally more colorful than lanthanides due to variable oxidation states and electronic transitions. --- (c) **Complex Stability: Actinides vs Lanthanides** **Explanation:** - Actinides often form more stable complexes due to larger size and higher charge density. **Final Answer:** Actinides form more stable complexes than lanthanides due to higher charge density and variable oxidation states. --- ### 9. (a) **Similarities: Lanthanides and Actinides** - Both have f-block elements. - Show +3 oxidation state. - Exhibit lanthanide/actinide contraction. - Similar chemical reactivity. - Form complexes. --- (b) **Distinguish Between Lanthanides and Actinides** - Lanthanides: 4f-block, mostly stable, less radioactive. - Actinides: 5f-block, many are radioactive, more variable oxidation states. --- ### 10. **Reduction of Thorium Oxides to Metal** **Methods:** 1. **Calcium reduction** 2. **Aluminium reduction (aluminothermic)** 3. **Electrolytic reduction** 4. **Magnesium reduction** --- ### 11. **Preparation Reactions** (i) **LaBr3:** La + 3Br2 → 2LaBr3 (ii) **La2(SO4)3·3Na2SO4·8H2O:** Mix La2(SO4)3 with Na2SO4 in water, crystallize. (iii) **La2(CO3)3:** La(NO3)3 + Na2CO3 → La2(CO3)3 + NaNO3 --- ### 12. **Consequences of Lanthanide Contraction** - Decrease in ionic/atomic radii. - Similarities in properties of post-lanthanide elements. - Difficulty in separation of lanthanides. - Increased density and hardness. --- ### 13. **Synthesis of Pu-239** **Steps:** 1. U-238 + n → U-239 2. U-239 → Np-239 (beta decay) 3. Np-239 → Pu-239 (beta decay) --- ### 14. **Uses of Plutonium** - Nuclear fuel (Pu-239 in reactors) - Nuclear weapons - Power source in space probes (radioisotope thermoelectric generators) - Research in nuclear chemistry --- If you need a detailed explanation or step-by-step answer to any specific question, let me know!