Lanthanide Contraction and Consequences - UNSOLVED PRACTICE SET
Chapter: d and f Block Elements | Topic: Lanthanide Contraction and Consequences
LANTHANIDE CONTRACTION AND CONSEQUENCES - UNSOLVED PRACTICE SET
Topic: Lanthanide Contraction and Consequences
Multiple Choice Questions
Q1. Lanthanide contraction is caused by:
- Increase in atomic number
- Poor shielding effect of 4f electrons
- Increase in principal quantum number
- Decrease in nuclear charge
Q2. As a result of lanthanide contraction:
- Atomic radii of the 5d and 6d series elements are very different
- Atomic radii of the 4d and 5d series elements become almost equal
- Atomic radii of the 3d and 4d series elements become almost equal
- There is no effect on atomic radii of transition elements
Q3. The pair of elements that have almost identical atomic radii due to lanthanide contraction is:
- Sc and Y
- Y and La
- Zr and Hf
- Nb and Ta
Q4. Lanthanide contraction results in:
- Similar chemical properties of lanthanides
- Difficulty in the separation of lanthanides
- Similar properties of 4d and 5d transition elements
- All of the above
Q5. The shielding effect of 4f electrons is:
- More than s and p electrons
- Less than s and p electrons but more than d electrons
- Less than d electrons
- Equal to all other electrons
Q6. Due to lanthanide contraction, the atomic radius of Hf is:
- Much larger than Zr
- Almost equal to Zr
- Much smaller than Zr
- Equal to Ti
Short Answer Questions
Q7. What is lanthanide contraction? Explain its cause in terms of poor shielding by 4f electrons.
Q8. Why does lanthanide contraction make the separation of lanthanides from each other very difficult?
Q9. How does lanthanide contraction affect the properties of elements that come after the lanthanides? Give one example.
Q10. Why do Zr and Hf have almost identical atomic radii and chemical properties? Explain using lanthanide contraction.
Q11. What would happen to the size of Hf if there were no lanthanide contraction? Compare the expected and actual sizes.
Q12. The density of 5d series elements is much higher than that of 4d series elements. How is this related to lanthanide contraction?
Long Answer Questions
Q13. (a) Define lanthanide contraction. Explain why it occurs.
(b) Describe the consequences of lanthanide contraction on:
(i) The properties of lanthanides themselves
(ii) The properties of post-lanthanide elements (5d series)
(iii) The separation of lanthanides
(c) Why is the shielding effect of f-electrons less effective than that of s, p, or d electrons?
Q14. (a) Explain why Zr and Hf, Nb and Ta, Mo and W show almost identical chemical properties.
(b) How does lanthanide contraction affect:
(i) Atomic and ionic radii
(ii) Density
(iii) Ionization energy
(iv) Electronegativity
Of the 5d series elements compared to the 4d series elements?
(c) Why is Hf found together with Zr in nature, making their separation difficult?
Q15. (a) Compare the atomic radii of the following pairs and explain the differences using lanthanide contraction:
(i) Ti (147 pm) and Zr (160 pm)
(ii) Zr (160 pm) and Hf (159 pm)
(iii) V (134 pm) and Nb (146 pm)
(iv) Nb (146 pm) and Ta (146 pm)
(b) What would be the expected trend in atomic radii across the transition series if lanthanide contraction did not exist? Draw a rough sketch showing the difference.
Numerical / Application-Based Problems
Q16. The following data compares atomic radii of 4d and 5d series elements:
| Element | 4d Series Radius (pm) | 5d Series Radius (pm) | Difference (pm) |
|---|---|---|---|
| Y | 180 | DataLa: 187 | ? |
| Zr | 160 | Hf: 159 | ? |
| Nb | 146 | Ta: 146 | ? |
| Mo | 139 | W: 139 | ? |
| Tc | 136 | Re: 137 | ? |
| Ru | 134 | Os: 135 | ? |
| Rh | 134 | Ir: 136 | ? |
| Pd | 137 | Pt: 139 | ? |
| Ag | 144 | Au: 144 | ? |
| Cd | 154 | Hg: 160 | ? |
(a) Complete the table by calculating the differences in radii.
(b) What trend do you observe in the differences between 4d and 5d series radii?
(c) Calculate the average difference in radius for the pairs Zr-Hf, Nb-Ta, and Mo-W.
(d) Compare this average with the difference between Y and La (187 180 = 7 pm). What does this comparison tell you about lanthanide contraction?
(e) Why is the difference between Cd and Hg (6 pm) larger than between Ag and Au (0 pm)?
Q17. The ionization energies (kJ/mol) of some elements are given below:
| Element | IE₁ | IE₂ | IE₃ |
|---|---|---|---|
| Zr | 640 | 1260 | 2220 |
| Hf | 642 | 1440 | 2250 |
| Nb | 652 | 1380 | 2416 |
| Ta | 761 | 1500 | 2100 |
(a) Compare the first ionization energies of Zr and Hf. Are they similar or different? Explain using lanthanide contraction.
(b) Compare the second ionization energies of Zr and Hf. Why is IE₂ of Hf significantly higher than that of Zr?
(c) The third ionization energy of Ta (2100 kJ/mol) is lower than expected. Suggest a reason.
(d) Calculate the average ionization energy (IE₁ + IE₂ + IE₃)/3 for Zr and Hf. What does this tell you about their overall stability?
(e) A chemist wants to separate Zr and Hf from a mineral sample. Why is this separation extremely difficult? What method might be used?
Q18. In a school science project, students investigate how lanthanide contraction affects everyday materials.
(a) A student finds that zirconium-based ceramics are used in dental crowns. Why is zirconia (ZrO₂) preferred over hafnia (HfO₂) for this application, despite their similar properties?
(b) Another student learns that hafnium is used in control rods of nuclear reactors. Why is Hf preferred over Zr for this purpose, even though they have almost identical chemical properties?
(c) A third student discovers that tantalum (Ta) is used in surgical implants because it is biocompatible and corrosion-resistant. Niobium (Nb) is also biocompatible. Why is Ta preferred over Nb for certain implants despite their similar chemistry?
(d) The students compare the prices of Zr and Hf compounds. Hf compounds are typically 10-100 times more expensive than Zr compounds. Why? (Consider abundance and separation difficulty.)
(e) The teacher asks: "If lanthanide contraction did not exist, how would the periodic table look different for elements 72-81?" Predict at least three differences.