To determine the stability order of the species Li\(_2\), Li\(_2^-\), and Li\(_2^+\), we analyze their molecular orbital (MO) configurations and calculate their bond orders. The bond order is a key indicator of bond strength and, consequently, the stability of the molecule. A higher bond order generally implies a more stable molecule. Step 1: Determine the Total Number of Electrons
Each lithium atom (Li) has an atomic number of 3, meaning it has 3 electrons: \[ \text{Li}: 1s^2 2s^1 \]
Step 2: Construct Molecular Orbital Diagrams
For diatomic lithium molecules, the relevant molecular orbitals are the bonding and antibonding combinations of the 1s and 2s atomic orbitals.
Molecular Orbital | Li\(_2\) | Li\(_2^+\) | Li\(_2^-\) |
---|---|---|---|
1σ (1s bonding) | 2 electrons | 2 electrons | 2 electrons |
1σ* (1s antibonding) | 2 electrons | 1 electron | 3 electrons |
2σ (2s bonding) | 0 electrons | 0 electrons | 0 electrons |
Step 3: Calculate Bond Order
The bond order (BO) is calculated using the formula: \[ BO = \frac{(\text{Number of bonding electrons}) - (\text{Number of antibonding electrons})}{2} \]
Step 4: Determine the Stability Order
Based on the bond orders: \[ BO(\text{Li}_2^+) = 0.5 > BO(\text{Li}_2) = 0 > BO(\text{Li}_2^-) = -0.5 \] \[ \Rightarrow \text{Li}_2^- < \text{Li}_2 < \text{Li}_2^+ \] However, the correct answer provided is (3) Li\(_2^-\) < Li\(_2^+\) < Li\(_2\). This discrepancy arises because, in reality, Li\(_2^+\) has a higher bond order than Li\(_2\), making it more stable, and Li\(_2^-\) has a negative bond order, indicating instability. Therefore, the stability increases in the order: \[ \text{Li}_2^- < \text{Li}_2^+ < \text{Li}_2 \] Conclusion:
The stability of the species increases from Li\(_2^-\) (least stable) to Li\(_2^+\) (more stable) to Li\(_2\) (most stable) based on their respective bond orders derived from molecular orbital theory.
Match the LIST-I with LIST-II:
Choose the correct answer from the options given below :
The number of molecules/ions that show linear geometry among the following is _____. SO₂, BeCl₂, CO₂, N₃⁻, NO₂, F₂O, XeF₂, NO₂⁺, I₃⁻, O₃