MO Diagrams for Heteronuclear Diatomic Molecules

• ThomasMagnus
In summary, the correct ordering of the σ and pi boxes in MO diagrams for heteronuclear molecules such as CO, HF, and NO depends on factors such as the s-p energy gap, orbital overlap, and relative energetic distance of the s and p orbitals on each atom. Calculations may be necessary to determine the correct order, but in some cases, the specific ordering may not be important if both orbitals are occupied. Various sources may use different methods, so it is important to consider the factors and use reliable resources when constructing MO diagrams.
ThomasMagnus
I'm trying to understand how to draw MO diagram for molecules such as CO, HF, and NO. I am finding so much conflicting information on how to order the σ and pi boxes in the diagram. Now, I know that the more electronegative atom's orbitals are going to be lower in energy than the less electronegative atom.

I have learned so far that there are two ways to set up MO diagrams for homo-nuclear diatomic molecules: one was with the pi 2p bonding MO below the σ2p bonding orbital and the reverse for atoms with an atomic number ≥8. How can this be applied to heteronuclear molecules? I keep finding different sources using both ways:

[PLAIN]http://i60.tinypic.com/20tgz61.png[/PLAIN]

[PLAIN]http://i62.tinypic.com/17bdwx.gif[/PLAIN]

Are both correct then?

Thanks!

The correct order of the orbitals depends on the s-p energy gap in both atoms, the relative energetic distance of the s and p orbitals on both atoms, respectively, the orbital overlapp etc. So to obtain the correct ordering will require a calculation.
You may try this yourself using e.g. some Extended Hueckel Calculators:
http://www.chembio.uoguelph.ca/educmat/chm715/software.htm
or
http://yaehmop.sourceforge.net/

On the other hand, the correct ordering is often not important, e.g. when both orbitals whose relative energy is unclear are both occupied.

1. What is a MO diagram for heteronuclear diatomic molecules?

A MO (Molecular Orbital) diagram is a graphical representation of the relative energies and bonding/antibonding character of the molecular orbitals formed from the combination of atomic orbitals in a heteronuclear diatomic molecule.

2. How is a MO diagram constructed?

A MO diagram is constructed by combining the atomic orbitals from the two atoms in a heteronuclear diatomic molecule, taking into account their relative energies and symmetries. The resulting molecular orbitals can be classified as bonding, non-bonding, or antibonding, depending on their relative energies.

3. What is the significance of the bond order in a MO diagram?

The bond order, which is the difference between the number of bonding and antibonding electrons in a MO diagram, is an indicator of the strength of the bond in a heteronuclear diatomic molecule. A higher bond order indicates a stronger bond.

4. How does the electronegativity difference between the two atoms affect the MO diagram?

The electronegativity difference between the two atoms in a heteronuclear diatomic molecule affects the relative energies of the atomic orbitals and, therefore, the resulting molecular orbitals. A larger electronegativity difference results in a greater degree of separation between the bonding and antibonding orbitals, leading to a stronger bond.

5. Can MO theory be used to predict the stability of heteronuclear diatomic molecules?

Yes, MO theory can be used to predict the stability of heteronuclear diatomic molecules. A more stable molecule will have a lower energy and a higher bond order in its MO diagram. Additionally, the relative energies of the molecular orbitals can also provide information about the reactivity of the molecule.

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