The lanthanides and actinides are located in which block of the periodic table?

Analysis

The question asks for the specific block in the periodic table where the lanthanides (elements 57–71) and actinides (elements 89–103) are positioned.

Concept Explanation

In the periodic table, elements are categorized into blocks based on the orbital that the highest-energy electron occupies:

• s-block: Groups 1 and 2 (alkali and alkaline earth metals).
• p-block: Groups 13 to 18 (excluding helium).
• d-block: Groups 3 to 12 (transition metals).
• f-block: These are the two rows detached from the main body of the periodic table. They are called the inner transition metals.

The lanthanides (also known as the lanthanoids) are filling the 4f subshell, while the actinides (also known as the actinoids) are filling the 5f subshell. Because their differentiating electrons enter the f-orbitals, they are collectively referred to as the f-block elements.

Step-by-Step Solution

1. Identify the groups: The main body of the periodic table contains the s, p, and d blocks.
2. Locate the detached rows: At the bottom of the standard periodic table, you will see two rows of 14 elements each.
3. Determine the orbital filling: These elements are characterized by the filling of the f-orbitals.
4. Conclusion: Since the lanthanides and actinides are the only elements that have their valence electrons in the f-orbitals, they are classified as the f-block elements.

Answer

The correct option is C.

Exam Tip

Think of the periodic table as a building: the s and p blocks are the main floors, the d block is the basement (transition metals), and the f block is the "sub-basement" or the detached annex at the bottom. Remember: f stands for far down!