Question

What is the electron configuration of nitrogen monoxide?

Answer 1

`(sigma_(1s))^2(sigma_(1s)^"*")^2(sigma_(2s))^2(sigma_(2s)^"*")^2(pi_(2p_x))^2(pi_(2p_y))^2(sigma_(2p_z))^2(pi_(2p_x)^"*")^1`

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This requires that we know what the molecular orbital (MO) diagram is for `"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:

• `1a_1` is the `sigma_(2s)` bonding MO.
• `2a_1` is the `sigma_(2s)^"*"` antibonding MO.
• `1b_1` is the `pi_(2p_x)` bonding MO.
• `1b_2` is the `pi_(2p_y)` bonding MO.
• `3a_1` is the `sigma_(2p_z)` bonding MO, but it's relatively nonbonding with respect to oxygen.
• `2b_1` is the `pi_(2p_x)^"*"` antibonding MO.
• `2b_2` is the `pi_(2p_y)^"*"` antibonding MO.
• `4a_1` is the `sigma_(2p_z)^"*"` antibonding MO.

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

We obtain:

`color(blue)((sigma_(1s))^2(sigma_(1s)^"*")^2(sigma_(2s))^2(sigma_(2s)^"*")^2(pi_(2p_x))^2(pi_(2p_y))^2(sigma_(2p_z))^2(pi_(2p_x)^"*")^1)`

Or, another way to write this is in the notation seen in the MO diagram, with `KK_(sigma)` indicating the filled `sigma_(1s)` and `sigma_(1s)^"*"` core orbitals:

`overbrace(color(blue)(KK_(sigma)))^((sigma_(1s))^2(sigma_(1s)^"*")^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)^"*")^1)`