What is the electron configuration of nitrogen monoxide?

Aug 8, 2017

${\left({\sigma}_{1 s}\right)}^{2} {\left({\sigma}_{1 s}^{\text{*")^2(sigma_(2s))^2(sigma_(2s)^"*")^2(pi_(2p_x))^2(pi_(2p_y))^2(sigma_(2p_z))^2(pi_(2p_x)^"*}}\right)}^{1}$

This requires that we know what the molecular orbital (MO) diagram is for $\text{NO}$; here it is (Miessler et al., Answer Key): (The original was this; I added the orbital depictions and symmetry labels.)

Quick overview of what the labels correspond to what MOs:

• $1 {a}_{1}$ is the ${\sigma}_{2 s}$ bonding MO.
• $2 {a}_{1}$ is the ${\sigma}_{2 s}^{\text{*}}$ antibonding MO.
• $1 {b}_{1}$ is the ${\pi}_{2 {p}_{x}}$ bonding MO.
• $1 {b}_{2}$ is the ${\pi}_{2 {p}_{y}}$ bonding MO.
• $3 {a}_{1}$ is the ${\sigma}_{2 {p}_{z}}$ bonding MO, but it's relatively nonbonding with respect to oxygen.
• $2 {b}_{1}$ is the ${\pi}_{2 {p}_{x}}^{\text{*}}$ antibonding MO.
• $2 {b}_{2}$ is the ${\pi}_{2 {p}_{y}}^{\text{*}}$ antibonding MO.
• $4 {a}_{1}$ is the ${\sigma}_{2 {p}_{z}}^{\text{*}}$ antibonding MO.

As a further note, the $2 s - 2 s$ overlap is the same idea as the $1 s - 1 s$ overlap. So, the molecular electron configuration would be written in a similar manner as the atomic counterpart, but using molecular orbitals instead.

We obtain:

$\textcolor{b l u e}{{\left({\sigma}_{1 s}\right)}^{2} {\left({\sigma}_{1 s}^{\text{*")^2(sigma_(2s))^2(sigma_(2s)^"*")^2(pi_(2p_x))^2(pi_(2p_y))^2(sigma_(2p_z))^2(pi_(2p_x)^"*}}\right)}^{1}}$

Or, another way to write this is in the notation seen in the MO diagram, with $K {K}_{\sigma}$ indicating the filled ${\sigma}_{1 s}$ and ${\sigma}_{1 s}^{\text{*}}$ core orbitals:

${\overbrace{\textcolor{b l u e}{K {K}_{\sigma}}}}^{{\left({\sigma}_{1 s}\right)}^{2} {\left({\sigma}_{1 s}^{\text{*")^2)underbrace(color(blue)((1a_1)^2(2a_1)^2))_((sigma_(2s))^2(sigma_(2s)^"*")^2)overbrace(color(blue)((1b_1)^2(1b_2)^2))^((pi_(2p_x))^2(pi_(2p_y))^2)overbrace(color(blue)((3a_1)^2))^((sigma_(2p_z))^2)underbrace(color(blue)((2b_1)^1))_((pi_(2p_x)^"*}}\right)}^{1}}$