Question

Write two similarities and two differences between lanthanoids and actinoids.

Hint:

Lanthanoids = 4f filling. Actinoids = 5f filling. Transition from 4f to 5f leads to easier ionization and higher radioactivity in actinoids.

Answer 1

Step 1: Understanding the Concept:
Lanthanoids (4f series) and Actinoids (5f series) are inner transition elements placed at the bottom of the periodic table.
Step 2: Detailed Explanation:
Similarities:
1. In both series, the last electron enters the f-orbital of the anti-penultimate shell (\( (n-2)f \)).
2. Both show a common and stable oxidation state of +3.
3. Both show a regular decrease in atomic and ionic radii with increasing atomic number (Lanthanoid and Actinoid contraction).

Differences:
1. Radioactivity: Most lanthanoids are non-radioactive (except Promethium). All actinoids are radioactive.
2. Oxidation States: Lanthanoids show limited oxidation states (+2, +3, +4). Actinoids show a wide range of oxidation states (up to +7) because the energy difference between 5f, 6d, and 7s orbitals is small.
3. Complex Formation: Actinoids have a much greater tendency to form complexes than lanthanoids.
Step 3: Final Answer:
Similarities include the common +3 oxidation state and filling of f-orbitals. Differences include radioactivity and the range of oxidation states.