Effective atomic number of Fe in `Fe_(2)(CO)_(9)` is

Options

A. 35
B. 36
C. 37
D. Cannot be calculated

Answer

To find the effective atomic number (EAN) of iron (Fe) in the coordination compound \( \text{Fe}_2(\text{CO})_9 \), we can follow these steps:

### Step 1: Identify the Atomic Number of Iron
The atomic number of iron (Fe) is 26.

### Step 2: Determine the Oxidation State of Iron
In this compound, carbon monoxide (CO) is a neutral ligand. Therefore, the oxidation state of iron in this complex is 0.

### Step 3: Count the Number of Ligands
In \( \text{Fe}_2(\text{CO})_9 \), there are 9 carbonyl (CO) ligands.

### Step 4: Calculate the Number of Electrons Donated by Ligands
Each CO ligand donates 2 electrons. Since there are 9 CO ligands, the total number of electrons donated by the ligands is:
\[ \text{Total electrons from ligands} = 9 \text{ ligands} \times 2 \text{ electrons/ligand} = 18 \text{ electrons} \]

### Step 5: Calculate the Effective Atomic Number (EAN)
The formula for calculating the effective atomic number is:
\[ \text{EAN} = Z - n + n_L \]
Where:
- \( Z \) = atomic number of the central atom (Fe) = 26
- \( n \) = oxidation state of the central atom = 0
- \( n_L \) = total number of electrons donated by ligands = 18

Substituting the values:
\[ \text{EAN} = 26 - 0 + 18 = 44 \]

### Conclusion
The effective atomic number of iron in \( \text{Fe}_2(\text{CO})_9 \) is **44**.

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