[Rutherford]

The MO theory always confuses me. Got 2  questions this time:

1)The electron arrangement in, for example, a N₂ molecule should look like this:
1s² 1*s² 2s² 2*s² 2p⁶
There are the bonding and anti-bonding orbitals filled, but where are the non-bonding orbitals? When are those filled?

2)When looking at the lewis structure of O₂ on google images, all the electrons are paired according that O₂ is diamagnetic, but when filling the MOs it is paramagnetic instead: 1s² 1*s² 2s² 2*s² 2p⁶ 2*p²(these are unpaired)
I assume that MO theory is more accurate, then why are the non-bonding electrons in O₂ structure written as pairs then?

[AWK]

In MO use σ and π instead of s and p.

http://depts.washington.edu/chemcrs/bulkdisk/chem162A_sum06/handout_Lecture_03.pdf

[Rutherford]

There is nothing about non-bonding orbitals.

[XGen]

I believe that for oxygen, the order of the 2nd shell orbital energy levels is:

2σ 2π 2σ* 2π*.

You have it listed as 2σ 2σ* 2π 2π*.

[Sophia7X]

The MO theory always confuses me. Got 2  questions this time:

1)The electron arrangement in, for example, a N₂ molecule should look like this:
1s² 1*s² 2s² 2*s² 2p⁶
There are the bonding and anti-bonding orbitals filled, but where are the non-bonding orbitals? When are those filled?

Non-bonding orbitals don't combine. MO diagrams explain bonding and show atomic orbitals combining to make molecular orbitals.

2)When looking at the lewis structure of O₂ on google images, all the electrons are paired according that O₂ is diamagnetic, but when filling the MOs it is paramagnetic instead: 1s² 1*s² 2s² 2*s² 2p⁶ 2*p²(these are unpaired)
I assume that MO theory is more accurate, then why are the non-bonding electrons in O₂ structure written as pairs then?

About 90% of the time, Lewis structure is a quick and easy way to accurately predict the structure of something. We have MO theory for that 10%  . MO theory is more accurate and according to molecular oxygen's MO diagram, it can actually be a biradical.

[Rutherford]

XGen I used a different easier, but not accurate way. I will switch to the real one.

Sophia, I didn't understand the diagram. Where does the 3σ come from? Why are the π orbitals non-bonding here and in O₂ they are bonding?

As I see from the link AWK gave, it is always started from σ_2s orbitals, are the σ_1s non-bonding here?

[Sophia7X]

That pic might be a little confusing, I got that pic off a British site. XD 3σ might be another way to say σ^*_sp. Also, don't take my explanation too seriously because my knowledge of MO theory is rather limited. If someone sees something wrong, don't hesitate to correct it.
Here might be a better pic:

From this pic, you can see 6 non bonding electrons.

Let's first talk about the definition of a non-bonding orbital. They have the same energy as the atomic orbital they were derived from. They're below anti-bonding orbitals in energy, and above bonding orbitals.
Non-bonding orbitals result when atomic orbitals cannot overlap because of dissimilar orientation.

The H-F sigma bond is formed from an electron from H1s and an electron from F2p_z. Now the left over 2p_x and 2p_y can't overlap with H orbitals. A sigma bond results when you have head-to-head overlap (on the internuclear axis, which is usually defined as the z axis). The remaining p orbitals are on the x and y axis  so they don't have the proper spatial orientation to overlap with H1s. 2s is also left over so you have 2 nonbonding fluorine 2p orbitals and 1 nonbonding 2s orbital. You can probably imagine that these 3 non-bonding orbitals keep the characteristics of the fluorine atomic orbital

[Rutherford]

I understood better now, but I don't see on the picture the 1s electrons of fluorine, shouldn't they be non-bonding, too?

[Sophia7X]

Yep. This picture only shows valence electrons so you don't see F1s.

[Rutherford]

Okay, thanks for helping me.