To determine which of the given species has the strongest O-O bond, we need to calculate the bond order for each species: O2, O2^+, O2^-, and O2^2-. The bond order can be calculated using the formula:
\[ \text{Bond Order} = \frac{1}{2} \left( \text{Number of electrons in bonding orbitals} - \text{Number of electrons in antibonding orbitals} \right) \]
### Step 1: Determine the Electron Configuration of O2
Oxygen (O) has 8 electrons, so O2 has a total of 16 electrons. The molecular orbital configuration for O2 is:
- σ(1s)² σ*(1s)²
- σ(2s)² σ*(2s)²
- σ(2p)², π(2p_x)², π(2p_y)², π*(2p_x)¹, π*(2p_y)¹
Counting the electrons:
- Bonding: 2 (σ(1s)) + 2 (σ(2s)) + 2 (σ(2p)) + 2 (π(2p_x)) + 2 (π(2p_y)) = 10
- Antibonding: 2 (σ*(1s)) + 2 (σ*(2s)) + 1 (π*(2p_x)) + 1 (π*(2p_y)) = 6
### Step 2: Calculate Bond Order for O2
Using the bond order formula:
\[ \text{Bond Order} = \frac{1}{2} (10 - 6) = \frac{4}{2} = 2 \]
### Step 3: Determine the Electron Configuration of O2^-
For O2^-, we add one additional electron:
- New configuration: σ(1s)² σ*(1s)² σ(2s)² σ*(2s)² σ(2p)², π(2p_x)², π(2p_y)², π*(2p_x)²
Counting the electrons:
- Bonding: 10 (same as O2)
- Antibonding: 6 + 1 = 7
Calculating bond order:
\[ \text{Bond Order} = \frac{1}{2} (10 - 7) = \frac{3}{2} = 1.5 \]
### Step 4: Determine the Electron Configuration of O2^2-
For O2^2-, we add two additional electrons:
- New configuration: σ(1s)² σ*(1s)² σ(2s)² σ*(2s)² σ(2p)², π(2p_x)², π(2p_y)², π*(2p_x)², π*(2p_y)²
Counting the electrons:
- Bonding: 10 (same as O2)
- Antibonding: 6 + 2 = 8
Calculating bond order:
\[ \text{Bond Order} = \frac{1}{2} (10 - 8) = \frac{2}{2} = 1 \]
### Step 5: Determine the Electron Configuration of O2^+
For O2^+, we remove one electron:
- New configuration: σ(1s)² σ*(1s)² σ(2s)² σ*(2s)² σ(2p)², π(2p_x)², π(2p_y)², π*(2p_x)²
Counting the electrons:
- Bonding: 10 (same as O2)
- Antibonding: 6 - 1 = 5
Calculating bond order:
\[ \text{Bond Order} = \frac{1}{2} (10 - 5) = \frac{5}{2} = 2.5 \]
### Step 6: Compare Bond Orders
Now we compare the bond orders:
- O2: 2
- O2^-: 1.5
- O2^2-: 1
- O2^+: 2.5
### Conclusion
The species with the strongest O-O bond is O2^+ with a bond order of 2.5.
