Actinides - Comparison with Lanthanides - UNSOLVED PRACTICE SET

Q7. Write the general electronic configuration of the actinides. How does it differ from that of the lanthanides?

Q8. Why do actinides show a greater range of oxidation states than lanthanides? Explain in terms of the energy difference between 5f and 6d orbitals.

Q9. Compare the radioactivity of lanthanides and actinides. Why are all actinides radioactive while most lanthanides are stable?

Q10. Why are actinide ions more easily hydrolyzed than lanthanide ions?

Q11. What is the actinide contraction? How does it compare with lanthanide contraction?

Q12. Uranium and plutonium are used in nuclear reactors. What property of these elements makes them suitable for nuclear energy?

Q13. (a) Compare the electronic configurations of lanthanides and actinides.

(b) Why do actinides show more variable oxidation states than lanthanides?

(c) Compare the radioactivity, toxicity, and chemical reactivity of lanthanides and actinides.

(d) Why are actinides called "inner transition elements" like lanthanides?

Q14. (a) Compare the following properties of lanthanides and actinides:

(i) Oxidation states

(ii) Complex formation tendency

(iii) Radioactivity

(iv) Chemical reactivity

(v) Spectral properties

(b) Why is the separation of actinides more difficult than that of lanthanides?

(c) Why are actinides not found in significant quantities in nature (except Th and U)?

Q15. (a) Describe the applications of actinides in:

(i) Nuclear energy

(ii) Medicine

(iii) Space exploration

(b) What are the environmental and health hazards associated with actinides?

(c) Why is the disposal of nuclear waste containing actinides a major challenge?

Q16. The following table compares some properties of lanthanides and actinides:

(a) Complete the table by filling in the missing information.

(b) The atomic radius of Ac is 188 pm, and that of Lr is 173 pm. Calculate the actinide contraction (total decrease in radius).

(c) Compare this with the lanthanide contraction (La³⁺ = 103 pm, Lu³⁺ = 86 pm, decrease = 17 pm). Is the actinide contraction larger or smaller? Give reasons.

(d) The density of uranium (19.1 g/cm³) is much higher than that of neodymium (7.0 g/cm³). Explain this difference.

(e) Calculate the number of moles in 1 kg of U-235. If each fission of U-235 releases 200 MeV of energy, calculate the total energy released from 1 kg of U-235. (1 MeV = 1.602 × 10⁻¹³ J)

Q17. Nuclear chemistry involves actinides in various applications:

(a) Uranium-235 undergoes fission when bombarded with slow neutrons. Write a representative fission reaction showing the formation of Ba-141 and Kr-92.

(b) Calculate the energy released in the above reaction using the following mass data:

Mass of U-235 = 235.0439 u

Mass of neutron = 1.0087 u

Mass of Ba-141 = 140.9144 u

Mass of Kr-92 = 91.9262 u

Mass of 3 neutrons = 3 × 1.0087 u

(1 u = 931.5 MeV/c²)

(c) Plutonium-239 is produced from U-238 in breeder reactors. Write the nuclear reactions involved.

(d) Why is Pu-239 preferred over U-235 in some nuclear weapons and reactors?

(e) A nuclear power plant produces 1000 MW of power. If the efficiency is 33%, calculate the mass of U-235 consumed per day.

Q18. In a school debate on "Nuclear Energy: Boon or Bane," students research actinides and their applications.

(a) One student argues that thorium is the "future fuel" for India. India has about 25% of the world's thorium reserves. Why is thorium considered safer than uranium for nuclear power? (Consider non-proliferation and waste aspects.)

(b) Another student mentions that smoke detectors contain americium-241. How does Am-241 detect smoke? What property of actinides is utilized here?

(c) A third student discusses the use of plutonium-238 in space missions (like Mars rovers). Why is Pu-238 ideal for powering spacecraft? What is this power source called?

(d) The students learn about the Chernobyl and Fukushima disasters. What actinides were released into the environment? Why are these elements particularly dangerous?

(e) The teacher asks: "If you were a policy maker, how would you balance India's energy needs with nuclear safety concerns?" Frame your response considering both scientific and ethical aspects.