Question

Draw the molecular orbital diagram of ${\mathrm{N}}_2$ and calculate the bond order.

Answer 1

Molecular orbital diagram:

• The molecular orbital diagram describes the chemical bonding in a molecule based on molecular orbital theory (MOT) and linear combination of atomic orbital(LCAO).
• The molecular orbital diagram has molecular orbital energy level at centre and is surrounded by atomic orbital energy level.
• It shows electrons in both bonding and anti-bonding molecular orbital.

Molecular orbital diagram of ${\mathrm{N}}_2$

Configuration of ${\mathrm{N}}_2$ : ${\left(\mathrm{\sigma }1\mathrm{s}\right)}^2{(\mathrm{\sigma }*1\mathrm{s})}^2{\left(\mathrm{\sigma }2\mathrm{s}\right)}^2{(\mathrm{\sigma }*2\mathrm{s})}^2{\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{x}}\right)}^2{\left(\mathrm{\pi }2{\mathrm{p}}_{\mathrm{y}}\right)}^2{\left(\mathrm{\sigma }2{\mathrm{p}}_{\mathrm{z}}\right)}^2$

Number of electrons in the bonding orbital$=10$

Number of electrons in the anti-bonding orbital$=4$

Bond order $$\begin{gathered} =\frac{1}{2}(\mathrm{number}\mathrm{of}\mathrm{bonding}\mathrm{electron}-\mathrm{number}\mathrm{of}\mathrm{antibonding}\mathrm{electrons}) \\ =\frac{1}{2}(10-4) \\ =\frac{1}{2}\times 6 \\ =3 \end{gathered}$$

Hence, bond order of ${\mathrm{N}}_2$ is 3.