Write the molecular orbital electronic configuration of peroxide and super oxide ions. Which out of these has higher bond order and why ?

Answer

To determine the molecular orbital electronic configurations of peroxide (O2^2-) and superoxide (O2^-), and to compare their bond orders, we will follow these steps:

### Step 1: Determine the number of electrons
- **Peroxide ion (O2^2-)**: It has 2 extra electrons compared to O2. Therefore, the total number of electrons = 16 (from O2) + 2 = 18 electrons.
- **Superoxide ion (O2^-)**: It has 1 extra electron compared to O2. Therefore, the total number of electrons = 16 (from O2) + 1 = 17 electrons.

### Step 2: Write the molecular orbital configuration for peroxide (O2^2-)
1. **1s orbital**:
- σ1s² (2 electrons)
- σ*1s² (2 electrons)
2. **2s orbital**:
- σ2s² (2 electrons)
- σ*2s² (2 electrons)
3. **2p orbital**:
- σ2p_z² (2 electrons)
- π2p_x² (2 electrons)
- π2p_y² (2 electrons)
- π*2p_x² (2 electrons)
- π*2p_y² (2 electrons)

Putting it all together, the molecular orbital configuration for peroxide (O2^2-) is:
\[ \sigma 1s^2 \sigma^* 1s^2 \sigma 2s^2 \sigma^* 2s^2 \sigma 2p_z^2 \pi 2p_x^2 \pi 2p_y^2 \pi^* 2p_x^2 \pi^* 2p_y^2 \]

### Step 3: Calculate the bond order for peroxide (O2^2-)
- **Bonding electrons**: 10 (from σ and π orbitals)
- **Antibonding electrons**: 8 (from σ* and π* orbitals)
- **Bond order formula**:
\[ \text{Bond Order} = \frac{(\text{Bonding Electrons} - \text{Antibonding Electrons})}{2} \]
\[ \text{Bond Order} = \frac{(10 - 8)}{2} = 1 \]

### Step 4: Write the molecular orbital configuration for superoxide (O2^-)
1. **1s orbital**:
- σ1s² (2 electrons)
- σ*1s² (2 electrons)
2. **2s orbital**:
- σ2s² (2 electrons)
- σ*2s² (2 electrons)
3. **2p orbital**:
- σ2p_z² (2 electrons)
- π2p_x² (2 electrons)
- π2p_y² (2 electrons)
- π*2p_x² (2 electrons)
- π*2p_y¹ (1 electron, since we have one less electron)

Putting it all together, the molecular orbital configuration for superoxide (O2^-) is:
\[ \sigma 1s^2 \sigma^* 1s^2 \sigma 2s^2 \sigma^* 2s^2 \sigma 2p_z^2 \pi 2p_x^2 \pi 2p_y^2 \pi^* 2p_x^2 \pi^* 2p_y^1 \]

### Step 5: Calculate the bond order for superoxide (O2^-)
- **Bonding electrons**: 10 (same as peroxide)
- **Antibonding electrons**: 7 (one less than peroxide, as one electron is removed from π*2p_y)
- **Bond order formula**:
\[ \text{Bond Order} = \frac{(\text{Bonding Electrons} - \text{Antibonding Electrons})}{2} \]
\[ \text{Bond Order} = \frac{(10 - 7)}{2} = 1.5 \]

### Step 6: Compare the bond orders
- **Peroxide (O2^2-)**: Bond order = 1
- **Superoxide (O2^-)**: Bond order = 1.5

### Conclusion
The superoxide ion (O2^-) has a higher bond order (1.5) compared to the peroxide ion (O2^2-) which has a bond order of 1. This indicates that superoxide has a stronger bond between the oxygen atoms than peroxide.