Write electronic configuration of `Fe^(2+)` and `Fe^(3+)` ions. Which of these has more number of unpaired electrons? Atomic no. of `Fe` is `26`.

Answer

To solve the problem, we will follow these steps:

### Step 1: Write the electronic configuration of neutral iron (Fe).
The atomic number of iron (Fe) is 26, which means it has 26 electrons. The electronic configuration can be written as follows:

1. Fill the 1s orbital: 1s²
2. Fill the 2s orbital: 2s²
3. Fill the 2p orbital: 2p⁶
4. Fill the 3s orbital: 3s²
5. Fill the 3p orbital: 3p⁶
6. Fill the 4s orbital: 4s²
7. Fill the 3d orbital: 3d⁶

Thus, the electronic configuration of neutral iron (Fe) is:
\[ \text{Fe: } 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^6 \]

### Step 2: Write the electronic configuration of the Fe²⁺ ion.
To form the Fe²⁺ ion, we need to remove 2 electrons from the neutral iron atom. The electrons are removed first from the outermost shell (4s) before the 3d shell. Therefore, we remove the 2 electrons from the 4s orbital:

- Remove 2 electrons from 4s²:
\[ 4s^2 \rightarrow 4s^0 \]
- The 3d remains the same:
\[ 3d^6 \]

Thus, the electronic configuration of Fe²⁺ is:
\[ \text{Fe}^{2+}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^0 \, 3d^6 \]

### Step 3: Write the electronic configuration of the Fe³⁺ ion.
To form the Fe³⁺ ion, we need to remove one additional electron from the Fe²⁺ configuration. This electron is removed from the 3d orbital:

- Remove 1 electron from 3d⁶:
\[ 3d^6 \rightarrow 3d^5 \]

Thus, the electronic configuration of Fe³⁺ is:
\[ \text{Fe}^{3+}: 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^0 \, 3d^5 \]

### Step 4: Determine the number of unpaired electrons in Fe²⁺ and Fe³⁺.
- For Fe²⁺ (3d⁶):
- The 3d subshell has 6 electrons. The distribution of electrons in the 3d subshell is as follows:
- 3d: ↑↓ ↑↓ ↑ ↑ ↑
- There are 4 unpaired electrons.

- For Fe³⁺ (3d⁵):
- The 3d subshell has 5 electrons. The distribution of electrons in the 3d subshell is as follows:
- 3d: ↑ ↑ ↑ ↑ ↑
- There are 5 unpaired electrons.

### Conclusion:
- The electronic configuration of Fe²⁺ is \( 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^0 \, 3d^6 \).
- The electronic configuration of Fe³⁺ is \( 1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^0 \, 3d^5 \).
- Fe³⁺ has more unpaired electrons (5 unpaired electrons) compared to Fe²⁺ (4 unpaired electrons).