Molecular Orbitals: Understanding & Rules

In summary, Molecular orbitals are the structures that atoms form when they are close together. There are two types of molecular orbitals- the bonding and the anti-bonding orbitals. The bonding orbitals can only hold two electrons and the anti-bonding orbitals can hold either one or two electrons. Excited electrons can move between the bonding and anti-bonding orbitals as long as the Pauli Exclusion principle isn't violated.
  • #1
nigelscott
135
4
My general understanding of Molecular Orbitals is as follows:

N atoms come together to form N molecular orbitals.

N/2 of the orbitals will be spatially asymmetric with symmetric spins.This corresponds to the antibonding orbital.

N/2 will be spatially symmetric with antisymmetric spins. This corresponds to the bonding orbital..

Each bonding orbital can contain a maximum of 2 electron with opposite spins.

Each antibonding orbital can either be empty or contain 1 electron since parallel spins in the same state are not allowed and with opposite spins the overall orbital would be symmetric which is not allowed for a fermion.

Excited electron can move to both higher energy bonding and antibonding orbitals as long as the Pauli Exclusion principle is not violated.

Is this the correct interpretation (particularly the last paragraph)?
 
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  • #2
Well, also anti-bonding orbitals can be occupied with 2 electrons whose spin has to be antiparallel then. On the other hand, bonding orbitals can also be empty.
 
  • #3
But if the spins are opposite in the anti-bonding case doesn't the overall wave function become symmetric which is not allowed for Fermions.
 
  • #4
If you have a product of two identical orbitals, this is always symmetric and you have to combine it with an antisymmetrric spin function. Could it be that you mixed this up with valence bond theory?
 
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  • #5
Yes, I think you are right. I think the thing that is throwing me is the usage of symmetric and antisymmetric. I understand this for AOs but maybe a better way to look at this for MOs is to replace these terms with constructive and destructive interference. Now what you are saying makes perfect sense. The bonding orbitals get filled first followed by the anti-bonding orbitals with the molecular stability being determined by the Bond Order.

I am not a chemist but a retired EE who is re-learning semiconductor band theory for fun!
 

1. What are molecular orbitals?

Molecular orbitals (MOs) are a concept in chemistry that describes the distribution of electrons in a molecule. They are formed by the overlapping of atomic orbitals, which are regions of space where an electron is most likely to be found.

2. How do molecular orbitals work?

Molecular orbitals are created by combining atomic orbitals of the same energy level and opposite spin. The electrons in these orbitals are delocalized, meaning they are not associated with a specific atom but are shared among all the atoms in the molecule. This allows for the formation of stable bonds between atoms.

3. What are the rules for filling molecular orbitals?

The rules for filling molecular orbitals are based on the Aufbau principle, Hund's rule, and the Pauli exclusion principle. According to the Aufbau principle, electrons fill the lowest energy orbitals first. Hund's rule states that electrons will occupy separate orbitals with the same energy before pairing up. The Pauli exclusion principle states that no two electrons can have the same set of quantum numbers (spin, energy, and position).

4. How are molecular orbitals different from atomic orbitals?

Molecular orbitals are formed by the combination of atomic orbitals, making them delocalized and shared among multiple atoms. In contrast, atomic orbitals are localized around a specific atom. Molecular orbitals also have different shapes and energy levels compared to atomic orbitals.

5. How are molecular orbitals used in chemistry?

Molecular orbitals are used to explain and predict the properties of molecules, such as their bond strength and reactivity. They also play a crucial role in understanding the electronic structure of molecules and how this affects their physical and chemical properties.

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