Wize University Chemistry Textbook > Molecular Orbital Theory
MO Diagrams of Main Group Elements [More Practice]
Example: MO Diagrams of 2s Block Molecules
MO Diagrams of 2p Block Molecules
s-p Mixing in MO Diagrams
Example: MO Diagrams with s-p Mixing
MO Diagrams without s-p Mixing - Example Problem
Practice Question: MO Diagrams of Homonuclear Diatomics
Practice Question: MO Diagrams of Neutral and Ionic Diatomics
Extra Practice
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MO Diagrams of 2s Block Molecules - Example Problem
Ex) Draw the MO Diagram of Be2. Is the molecule stable? What is its bond order?
See video for MO diagram. Be2 is NOT a stable molecule, because it has a bond order of 0.
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MO Diagrams of 2p Block Molecules
- The 2p orbitals combine to produce a orbital and a orbital, and two orbitals and two orbitals.
Ex) B2
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s-p Mixing in MO Diagrams
- Of the Main Group Elements (Li, Be, B, C, N, O, F, Ne), the gap between the 2s and 2p orbitals increases as you go across (left-to-right) the Periodic Table because atomic size decreases, which stabilizes the 2s orbital more than the 2p orbitals, and thus the gap widens. For these reasons, Molecules formed with atoms of Z7 (e.g., Li2, Be2, B2, C2 and N2) have s-p mixing. Molecules formed with atoms of Z8 do not have s-p mixing (e.g., O2, F2 and Ne2).
- When there is s-p mixing, theorbitals have better orbital overlap, more so than theorbital, and hence theorbitals are lower in energy than theorbital.
- When there is no s-p mixing, theorbital has better orbital overlap than theorbitals, and hence theorbital is lower in energy than theorbitals.
- Note that theorbitals are ALWAYS lower in energy than theorbital because theorbitals have less nodes than theorbital.
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MO Diagrams with s-p Mixing - Example Problem
Ex) Draw the MO diagram of N2. Determine the bond order and magnetism of the molecule.
See video for MO diagram. The bond order is 3. The molecule is diamagnetic.
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MO Diagrams without s-p Mixing - Example Problem
Ex) Draw the MO diagram of O2. Determine the bond order and magnetism of the molecule.
See video for MO diagram. The bond order is 2 and the molecule is paramagnetic.
Mark Yourself Question
- Grab a piece of paper and try this problem yourself.
- When you're done, check the "I have answered this question" box below.
- View the solution and report whether you got it right or wrong.
Practice Question: MO Diagrams of Homonuclear Diatomics
A student has an unknown, homonuclear diatomic, meaning the two atoms in the molecule are of the same element. The student knows the atomic number of the element is less than 10, and that the atoms are paramagnetic but the molecule is diamangnetic. Using the MO diagram below, determine the identity of this molecule.
Mark Yourself Question
- Grab a piece of paper and try this problem yourself.
- When you're done, check the "I have answered this question" box below.
- View the solution and report whether you got it right or wrong.
Practice Question: MO Diagrams of Neutral and Ionic Diatomics
Using MO diagrams, rank the following atoms in order of decreasing bond length: O2, O2+ and O2-.