Applications of the Molecular Orbital Theory
- In molecular orbital theory (MO theory), atomic orbitals from different atoms are mixed to form molecular orbitals.
- MO theory predicts that dinitrogen (N 2 ) is diamagnetic while dioxygen (O 2 ) is paramagnetic.
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- In molecular orbital theory (MO theory), atomic orbitals from different atoms are mixed to form molecular orbitals. Whenever two orbitals are mixed, a bonding orbital (with high electron probability density between the nuclei) is formed, as well as an antibonding orbital (with a node in electron probability density between the nuclei).
- For example, when two 2s orbitals from two nuclei are mixed, a bonding orbital is formed ( 2s ) as well as an antibonding orbital ( * 2s ). Sigma molecular orbitals (such as 2s ) have electron density between the atoms forming the bond, while pi molecular orbitals (such as 2py ) have electron density above and below the sigma molecular orbital.
- Molecular orbitals fill from lowest to highest energy following Hund’s rule and the Pauli exclusion principle.
- In dinitrogen (N 2 ), this results in four filled bonding orbitals (sigma 2s, sigma 2pz, pi 2px, and pi 2py ) and one filled antibonding orbital ( sigma* 2s ), with no unpaired electrons. Therefore, N 2 is diamagnetic (N 2 is not attracted to a magnetic field).
- In dioxygen (O 2 ), this results in four filled bonding orbitals (sigma 2s, sigma 2pz, pi 2px, and pi 2py), one filled antibonding orbital (sigma* 2s ), and two unpair
Which statement about electrons is not true?
When there is a minimum number of electrons between atoms, there is a high probability of bonding
What is the main weakness of hybridization theory?
It does not acknowledge the fact that electrons do spend time away from their parent nuclei.
Which statement about the nitrogen molecule is not correct?
The bond order is 4.
Why is the energy ladder only helpful for elements that have numbers of 18 or less?
If the element had a higher atomic number, you would have to include orbital sites higher than 2p.
Which statement about the bonding and anti-bonding sites in the 2s and 2p valence orbitals is not true?
The greatest bond order value is four.
When we looked at assigning the electrons in nitrogen to sites in the 2s and 2p orbitals, we used the 2s anti-bonding site. Which statement about this site is not true?
The energy level for this site is very similar to the energy level for the σ 2s orbital site.
Look at the lower energy, more stable sites in the 2p level (indicated by the arrows).
Which of the following statements is the weakest explanation for why there are two π orbital sites within the 2p level?
These sites are at lower energies than the π orbital sites in the 2p level.
Which statement about the electron site assignments in the oxygen molecule is not correct?
The assignment of two lone electrons in the π* orbital does not have a great effect on any physical properties of the oxygen molecule.
Which statement about the forming of orbitals (for n = 2) is not true?
A σ bond and a σ* (anti-) bond have similar energy levels.
Which of the following shows the correct order—from least to greatest energy—for the bond types found in 2s and 2p orbitals for the O2 molecule (for n = 2)?
one 2s σ bond, one 2s σ* bond, one 2p σ bond, two 2p π bonds, two 2p π* bonds, one 2p σ* bond