# What is the molecular electron configuration of #"O"_2#?

##### 1 Answer

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

You should read the explanation on how we came up with this, below.

When determining the molecular orbital (MO) configuration of a *homonuclear diatomic* molecule like

We had for each

#1s^2 2s^2 2p^4#

The AOs of

**LINEAR COMBINATION OF ATOMIC ORBITALS**

*The number of AOs in equals the number of MOs out.*

Any *head-on*:

**In**-phase to form#sigma_(ns)# /sigma**bonding**MOs**Out-of**-phase to form#sigma_(ns)^"*"# **antibonding**MOs

The

with a partial MO diagram like this:

Along the internuclear (*head-on* in a similar manner:

**In**-phase to form#sigma_(np_z)# **bonding**MOs**Out-of**-phase to form#sigma_(np_z)^"*"# **antibonding**MOs

Here's how the

The partial MO diagram depiction of those is similar to the

Finally, the *sidelong/sideways*, so that they make

For homonuclear diatomics *after* **energy ordering** is like this for these six MOs:

This portion of the MO diagram (the

Overall, the **MO diagram** is therefore like this:

The MOs were filled just like the AOs would be filled according to the Aufbau Principle, Hund's Rule, and the Pauli Exclusion Principle.

So, write the MO configuration based on this diagram. Start with the lowest-energy orbital, and indicate the electrons in each kind of orbital, just like atomic electron configurations.

You should get:

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