CHEMISTRY COMMUNITY

So, MO theory allows us to find the bonding order and the magnetic properties but why does knowing those things help us i.e. what are they for?

Using molecular orbital theory one can calculate and predict the dissociation energy of a reaction, including new reactions and biological reactions.

It can also be used to calculate enzyme catalyzed reactions and gain understanding of why one reaction pathway is faster than another.

Magnetic storage devices are based on the use of different patterns of magnetisation corresponding to information in stored data. This is basis for all stored data in computers.

Take a look at the last page of molecular orbital theory in your courses reader. I gave this biological example as plants having a green color can be explained based on chlorophyll absorption bands (again molecular orbital theory).

See my additional comments at: https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=43&t=16941&p=44048

Wow, very interesting. Thank you!

To add on...Molecular orbital theory allows us to understand the probability of finding the electrons at particular points around the molecule. MO Theory also allows us to understand bond order which is significant for the understanding of reactivities. Prior to learning about MO, we learned about the significant role of atomic orbitals. Understanding electron configuration, it was understood that these such orbitals contain electrons attributed to a single atom. In contrast, molecular orbitals, which encompass a number of atoms in a molecule, contain valence electrons between atoms. Therefore, the MO theory is important for understanding the study of bonding by approximating the positions of bonded electrons (the molecular orbitals) in reference to atomic orbitals.

Is MO theory vital to understanding coordination and ligands?

If it helps to find disassociation energy, how does it do so?

How do we find bond order from a molecular orbital diagram?

Bond order = 1/2 (Number of electrons in bonding orbitals - number of electrons in antibonding orbitals)

The antibonding orbitals are the orbitals marked with an asterisk (*). You draw the molecular orbital diagram, then count the number of electrons in the bonding and antibonding orbitals, and then use the formula above to calculate the bond order.

JELCI_BARRAZA_1C wrote:Is MO theory vital to understanding coordination and ligands?

MO theory is not needed to understand coordination compounds.

Brian_Mena_4G wrote:If it helps to find disassociation energy, how does it do so?

The calculations are detailed and give the disassociation energy. Doing this would be an advanced quantum chemistry class.

I mentioned in class that we are not doing the calculations that give the specific energy values for each molecule.
We are using the molecular orbital diagrams.

I have a very basic question regarding drawing the molecular orbital diagrams.

Just to confirm, we draw the diagram using the number of valence electrons not the atomic number. But the atomic number determines which type of molecular orbital diagram we draw. (Z>=8 or Z<8)?

Thank you.

Minu Reddy 3F wrote:I have a very basic question regarding drawing the molecular orbital diagrams.

Just to confirm, we draw the diagram using the number of valence electrons not the atomic number.
But the atomic number determines which type of molecular orbital diagram we draw. (Z>=8 or Z<8)?

Thank you.

Yes. Well stated. Introduce yourself at the end of class.

MO theory is also useful for predicting which atom could be most prone to bonding based on the higher contribution to the LUMO, as well as reactivity based on lone pairs in the molecular orbitals.

Molecular Orbital Theory gives us more understanding of molecules we may not be able to know just through Lewis structures. It mainly gives us context on bond strength and magnetic properties. We can figure out the bond order through MO theory, and the higher the bond order, the stronger the bond. We can use this to find the relative strength of bonds between different atoms. The MO Energy Level Diagram can visually show us whether or not there are unpaired electrons, showing whether the molecule is diamagnetic (repels the magnetic field) or paramagnetic (attracts the magnetic field).
Generally, Lewis structures will give the correct unpaired and paired electrons but, O2 is a good example of how MO Theory can give us a better understanding beyond the Lewis Structure understanding. MO Theory for O2 shows that it is paramagnetic because it has 2 unpaired electrons. However, the Lewis structure shows O2 sharing a double bond with 2 pairs of lone pairs on each Oxygen atom.

MO diagrams help us determine stability of the bonds, relative electronegativity, paramagnetic or diamagnetic properties, and bond order. All of these help us determine the characteristics of the molecule in question.

MO theory helps you determine the characteristics of the bonding between two things. It can tell you the strength of the bond, the types of bonds and the antibonding/bonding electrons.

When we are determining whether to use the z>8 or z<8 diagram for a molecule, which atom do we look at? Like for example for, NO, do we look at the z for nitrogen or oxygen ?

For heteronuclear molecules (like NO), we always stick with the MO diagram for z<8. That's what the TA told us when we went his review.

What is an example of a molecule that you would use the MO diagram z>8?

Janice Kim 3I wrote:Molecular Orbital Theory gives us more understanding of molecules we may not be able to know just through Lewis structures. It mainly gives us context on bond strength and magnetic properties. We can figure out the bond order through MO theory, and the higher the bond order, the stronger the bond. We can use this to find the relative strength of bonds between different atoms. The MO Energy Level Diagram can visually show us whether or not there are unpaired electrons, showing whether the molecule is diamagnetic (repels the magnetic field) or paramagnetic (attracts the magnetic field).
Generally, Lewis structures will give the correct unpaired and paired electrons but, O2 is a good example of how MO Theory can give us a better understanding beyond the Lewis Structure understanding. MO Theory for O2 shows that it is paramagnetic because it has 2 unpaired electrons. However, the Lewis structure shows O2 sharing a double bond with 2 pairs of lone pairs on each Oxygen atom.

Yes, from what I understand in a very basic sense is that MO theory accounts for shortcomings of VB theory and Lewis's work.

How does the number of paired or unpaired electrons relate to the magnetism of a molecule?