Question

Consider the following species: \[ Li_2,\; B_2,\; Be_2,\; C_2,\; O_2,\; O_2^{2-},\; F_2 \] The number of species with bond order value 1 is:

• A. 2
• B. 4
• C. 3
• D. 5

Hint:

Stable molecules generally have bond order \(>0\). Larger bond order implies greater stability and shorter bond length.

Answer 1

The Correct Option is B

Concept: According to Molecular Orbital Theory, \[ \text{Bond Order} = \frac{N_b-N_a}{2} \] where \(N_b\) is the number of bonding electrons and \(N_a\) is the number of antibonding electrons.

Step 1: Find bond order of each species.
\[ Li_2 \] Electronic configuration: \[ (\sigma_{1s})^2(\sigma_{1s}^{*})^2(\sigma_{2s})^2 \] \[ BO=\frac{2-0}{2}=1 \] \[ Be_2 \] \[ BO=\frac{2-2}{2}=0 \] \[ B_2 \] \[ BO=1 \] \[ C_2 \] \[ BO=2 \] \[ O_2 \] \[ BO=2 \] \[ O_2^{2-} \] Addition of two electrons reduces bond order to \[ BO=1 \] \[ F_2 \] \[ BO=1 \]

Step 2: Count species with bond order 1.
They are: \[ Li_2,\; B_2,\; O_2^{2-},\; F_2 \] Total \[ \boxed{4} \]