Question

The EAN of cobalt in the complex [Co(NH3)6]3+ is:

• A. 27
• B. 30
• C. 33
• D. 36

Hint:

The EAN rule (Sidgwick's rule) suggests that stable complexes often have an EAN equal to the atomic number of the next noble gas. Cobalt's next noble gas is Krypton (\( Z = 36 \)), which helps verify your calculation.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks for the Effective Atomic Number (EAN) of the central metal atom, cobalt (Co), in the coordination complex [Co(NH$_{3}$)$_{6}$]$^{3+}$.

Step 2: Key Formula or Approach:
The Effective Atomic Number (EAN) can be calculated using the formula:
\[ \text{EAN} = Z - \text{ON} + (2 \times \text{CN}) \] Where:
- \( Z \) is the atomic number of the central metal.
- \(\text{ON}\) is the oxidation state of the central metal.
- \(\text{CN}\) is the coordination number (number of ligands if they are monodentate).

Step 3: Detailed Explanation:
1. Atomic number (\( Z \)): For cobalt (Co), \( Z = 27 \).
2. Oxidation State (\(\text{ON}\)): Let the oxidation state of Co be \( x \).
Ammonia (NH$_{3}$) is a neutral ligand, so its charge is 0.
Sum of charges: \( x + 6(0) = +3 \Rightarrow x = +3 \).
So, the oxidation state of cobalt is +3.
3. Coordination Number (\(\text{CN}\)): There are six NH$_{3}$ ligands attached to the cobalt atom. Since NH$_{3}$ is a monodentate ligand, the coordination number is 6.
4. Calculate EAN:
\[ \text{EAN} = 27 - 3 + (2 \times 6) \] \[ \text{EAN} = 24 + 12 = 36 \]

Step 4: Final Answer:
The EAN of cobalt in the complex [Co(NH$_{3}$)$_{6}$]$^{3+}$ is 36, which corresponds to the atomic number of the noble gas Krypton (Kr).