# Chemical Anti-bonding and Pauli repulsion [closed]

We can explain chemical anti-bonding just using the Pauli repulsion correct?Let's take He2.

2 atoms of He share 4 1s electrons and since the magnetic spin for electrons has 2 values there would be 2 electrons with the same wave function which would violate the Pauli exclusion principle.This makes He2 unstable and it disassociates in 2 He atoms

Am I correct?

• The anti-bonding orbitals still obey the Pauli principle. You mixed up two different unrelated things. – Greg Nov 6 '19 at 3:38
• No I say that the antibonding orbitals exist due to Pauli exclusion principle. – Mrs Chemistry Nov 6 '19 at 3:40
• Let's put it this way: all orbitals except the lowest one are occupied due to Pauli exclusion principle. This applies to atoms as well. He2 is the only system where this is important for the molecule, but not for the atoms. – Ivan Neretin Nov 6 '19 at 6:32
• Orbitals do not exist in a physical sense. You can argue, as @IvanNeretin that occupation of higher energy levels occurs because of the Pauli principle (without that all electrons would go to a single orbital), but those different orbitals (single-electron energy level) exist because they are solutions for the Schrodinger equation. – Greg Nov 6 '19 at 16:36
• I know all of this ok?Just the existence of antibonding orbitals is due to the Pauli exclusion principle.In He2 there are 4 electrons in the same orbital ->2 of them must have the same wavefunction and this makes He2 unstable. – Mrs Chemistry Nov 6 '19 at 18:55

The reason we speak of orbitals as being exclusively inhabited by 2 (max) electrons (with opposing electron spin quantum number) is because electrons are fermions and therefore observe the exclusion principle. The exclusion principle constrains the allowed electron configurations, disallowing occupation of lower E orbitals by more than 2 electrons. In the case of $$\ce{He2}$$ it requires occupation of orbitals that raise the total E above the energy of the atoms at greater separation. So, in a word, the answer is yes.