Question

In the periodic table, actinoids belong to:

• A. s-block
• B. p-block
• C. d-block
• D. f-block

Hint:

The f-block elements are known as inner transition elements.
The lanthanoids represent the \(4f\) series in period 6, while the actinoids represent the \(5f\) series in period 7.
Remembering this structure helps in solving basic periodic table placement questions.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the specific block of the modern periodic table to which actinoids belong.

Step 2: Key Formula or Approach:
The block classification in the periodic table is determined by the subshell into which the differentiating (last) electron enters.

Step 3: Detailed Explanation:

• Actinoid Series Definition: Actinoids consist of the 14 elements following Actinium, ranging from Thorium (\(Th\), \(Z = 90\)) to Lawrencium (\(Lr\), \(Z = 103\)).
  
• Electronic Configuration: In these elements, the differentiating electrons progressively fill the \(5f\) inner-transition subshell.
  
• Definition of f-block: Elements in which the \(4f\) and \(5f\) orbitals are progressively filled are classified as f-block elements.
  
• Comparing Other Blocks:
  
  • s-block: Comprises Groups 1 and 2, where the outermost s-orbital is filled.
    
  • p-block: Comprises Groups 13 to 18, where the outermost p-orbitals are filled.
    
  • d-block: Comprises transition elements of Groups 3 to 12, where the d-orbitals are filled.
    
• Position in Periodic Table: The f-block is placed at the bottom of the periodic table as two separate horizontal rows to maintain structural symmetry.
  

Step 4: Final Answer:
Therefore, actinoids belong to the f-block, which matches option (D).