Ch.10 - Molecular Shapes & Valence Bond TheorySee all chapters
All Chapters
Ch.1 - Intro to General Chemistry
Ch.2 - Atoms & Elements
Ch.3 - Chemical Reactions
BONUS: Lab Techniques and Procedures
BONUS: Mathematical Operations and Functions
Ch.4 - Chemical Quantities & Aqueous Reactions
Ch.5 - Gases
Ch.6 - Thermochemistry
Ch.7 - Quantum Mechanics
Ch.8 - Periodic Properties of the Elements
Ch.9 - Bonding & Molecular Structure
Ch.10 - Molecular Shapes & Valence Bond Theory
Ch.11 - Liquids, Solids & Intermolecular Forces
Ch.12 - Solutions
Ch.13 - Chemical Kinetics
Ch.14 - Chemical Equilibrium
Ch.15 - Acid and Base Equilibrium
Ch.16 - Aqueous Equilibrium
Ch. 17 - Chemical Thermodynamics
Ch.18 - Electrochemistry
Ch.19 - Nuclear Chemistry
Ch.20 - Organic Chemistry
Ch.22 - Chemistry of the Nonmetals
Ch.23 - Transition Metals and Coordination Compounds

Molecular Orbital Theory allows us to predict the distribution of electrons within a molecule. This allows us to predict properties such as bond order, magnetism and shape

Molecular Orbital (MO) Theory

Concept #1: Understanding Molecular Orbital Theory

In MO theory, electrons are seen as being delocalized or spread out over a molecule instead of concentrated in a covalent bond. 

Example #1: Use a MO diagram to write the electron configuration of each of the following:

C22-

Example #2: Use a MO diagram to write the electron configuration of each of the following:

F2+

Bond Order

Concept #2: Calculating Bond Order

By calculating the bond order it is possible to determine the stability of the bonds within a molecule. 

Practice: Use a MO diagram to determine if the following compound exists or not. 

O2 2- and B-

Additional Problems
Which statement about bonding molecular orbitals is incorrect? a. Electrons in bonding orbitals tend to stabilize the molecule. b. Only s bonds can result from bonding molecular orbitals. c. In a bonding molecular orbital, the electron density is high between the two atoms. d. Bonding molecular orbitals result from addition of the wave functions of the atomic orbitals. e. The relative numbers of electrons in bonding versus antibonding orbitals determines the overall stability of the molecule.
 All of the following statements concerning molecular orbital (MO) theory are correct EXCEPT a. The Pauli exclusion principle is obeyed. b. Hund’s rule is obeyed. c. The combination of two atomic orbitals creates one molecular orbital. d. A bonding molecular orbital is lower in energy than its parent atomic orbitals. e. Electrons are assigned to orbitals of successively higher energy. 
According to the molecular orbital (MO) theory, overlap of two s atomic orbitals produces which of the following? a) one antibonding molecular orbital and one hybrid orbital b) two antibonding molecular orbitals c) one bonding molecular orbital and one antibonding molecular orbital d) two bonding molecular orbitals and one antibonding molecular orbital e) two bonding molecular orbitals and two antibonding molecular orbitals
The following is part of a molecular orbital energy-level diagram for MOs constructed from 1s atomic orbitals. You may want to reference (Pages 369 - 371) Section 9.7 while completing this problem.What labels do we use for the two MOs shown?
The following is part of a molecular orbital energy-level diagram for MOs constructed from 1s atomic orbitals. You may want to reference (Pages 369 - 371) Section 9.7 while completing this problem.If an electron is added to the system, into which of the MOs will it be added?
Molecules that are brightly colored have a small energy gap between filled and empty electronic states (the HOMO-LUMO gap). Sometimes you can visually tell which HOMO-LUMO gap is larger for one molecule than another.Suppose you have samples of two crystalline powders—one is white, and one is green. Which one has the larger HOMO-LUMO gap?
What is the difference between hybrid orbitals and molecular orbitals?
How many electrons can be placed into each MO of a molecule?
Can antibonding molecular orbitals have electrons in them?
You may want to reference (Pages 372 - 382) Section 9.8 while completing this problem.If you combine two atomic orbitals on two different atoms to make a new orbital or on only one atom to make a new orbital, is a hybrid orbital or a molecular orbital formed?
Draw a picture that shows all three 2p orbitals on one atom and all three 2p orbitals on another atom. Imagine the atoms coming close together to bond.How many 2p bonds can the two sets of 2p orbitals make with each other?
Draw a picture that shows all three 2p orbitals on one atom and all three 2p orbitals on another atom. Imagine the atoms coming close together to bond.How many 2p bonds can the two sets of 2p orbitals make with each other?
The energy-level diagram in the figure above shows that the sideways overlap of a pair of pandoc: Error at "source" (line 1, column 97): unexpected " " expecting "{" or "" p orbitals produces two molecular orbitals, one bonding and one antibonding. In ethylene there is a pair of electrons in the bonding pi orbital between the two carbons. Absorption of a photon of the appropriate wavelength can result in promotion of one of the bonding electrons from the pi _{2p} to the pi _{2p}^ ast molecular orbital.Assuming this electronic transition corresponds to the HOMO-LUMO transition, what is the LUMO in ethylene?
The energy-level diagram in the figure above shows that the sideways overlap of a pair of pandoc: Error at "source" (line 1, column 97): unexpected " " expecting "{" or "" p orbitals produces two molecular orbitals, one bonding and one antibonding. In ethylene there is a pair of electrons in the bonding pi orbital between the two carbons. Absorption of a photon of the appropriate wavelength can result in promotion of one of the bonding electrons from the pi _{2p} to the pi _{2p}^ ast molecular orbital.Is the C-C bond in ethylene easier to twist in the ground state or in the excited state?
How does each of the three major bonding theories (Lewis theory, valence bond theory, and molecular orbital theory) define a single chemical bond? A double bond? A triple bond? How are these definitions similar? How are they different?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown on the picture below .How many molecular orbitals are there in the diagram?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown on the picture below .How many nodes are in the lowest-energy molecular orbital?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown on the picture below .How many nodes are in the highest-energy molecular orbital?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown on the picture below .How many nodes are in the highest-energy occupied molecular orbital (HOMO)?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown on the picture below .How many nodes are there in the lowest-energy unoccupied molecular orbital (LUMO)?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown on the picture below .How does the HOMO-LUMO energy gap for this case compare to that of the four-atom case?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown on the picture below .Choose the correct molecular-orbital diagram for a chain containing six lithium atoms.
The electronic band structure of nickel.If the metal were potassium rather than nickel, which bands- 4s, 4p, and/or 3d -would be partially occupied?
We have learned that the Lewis model portrays a chemical bond as the transfer or sharing of electrons represented as dots. Valence bond theory portrays a chemical bond as the overlap of two half-filled atomic orbitals. What is a chemical bond according to molecular orbital theory?
Which element, W or Au, has the greater number of electrons in antibonding orbitals?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown in Figure 12.23 in the textbook. Construct a molecular-orbital diagram for a chain containing eight lithium atoms and use it to answer the following questions.How many molecular orbitals are there in the diagram?
What is a chemical bond according to molecular orbital theory?
Explain the difference between hybrid atomic orbitals in valence bond theory and LCAO molecular orbitals in molecular orbital theory.
The effect of interactions between 2s and 2p atomic orbitals.Which molecular orbitals have switched relative energy in the group on the right as compared with the group on the left?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown in Figure 12.23 in the textbook. Construct a molecular-orbital diagram for a chain containing eight lithium atoms and use it to answer the following questions.How many nodes are in the highest-energy occupied molecular orbital (HOMO)?
What is a bonding molecular orbital?
The molecular-orbital diagrams for two- and four-atom linear chains of lithium atoms are shown in Figure 12.23 in the textbook. Construct a molecular-orbital diagram for a chain containing eight lithium atoms and use it to answer the following questions.How many nodes are in the lowest-energy unoccupied molecular orbital (LUMO)?
What is an antibonding molecular orbital?
What is the role of wave interference in determining whether a molecular orbital is bonding or antibonding?
In molecular orbital theory, what is bond order?
How is the number of molecular orbitals approximated by a linear combination of atomic orbitals related to the number of atomic orbitals used in the approximation?
When applying molecular orbital theory to heteronuclear diatomic molecules, the atomic orbitals used may be of different energies.If two atomic orbitals of different energies make two molecular orbitals, how are the energies of the molecular orbitals related to the energies of the atomic orbitals?
When applying molecular orbital theory to heteronuclear diatomic molecules, the atomic orbitals used may be of different energies.How is the shape of the resultant molecular orbitals related to the shapes of the atomic orbitals?
In molecular orbital theory, what is a nonbonding orbital?
Write a short paragraph describing chemical bonding according to Lewis theory, valence bond theory, and molecular orbital theory. Indicate how the theories differ in their description of a chemical bond and indicate the strengths and weaknesses of each theory. Which theory is correct?
The organic molecules shown beloware derivatives of benzene in which additional six-membered rings are "fused" at the edges of the hexagons. The compounds are shown in the usual abbreviated method for organic molecules.Benzene, naphthalene, and anthracene are colorless, but tetracene is orange. What does this imply about the relative HOMO-LUMO energy gaps in these molecules? See the "Chemistry Put to Work" box in the textbook on Orbitals and Energy.
For each of these contour representations of molecular orbitals, identify: The atomic orbitals (s or p) used to construct the MO
For each of these contour representations of molecular orbitals, identify: The type of MO (sigma or pi)
For each of these contour representations of molecular orbitals, identify: Whether the MO is bonding or antibonding?
For each of these contour representations of molecular orbitals, identify: The atomic orbitals (s or p) used to construct the MO
For each of these contour representations of molecular orbitals, identify: The type of MO (sigma or pi)
For each of these contour representations of molecular orbitals, identify: Whether the MO is bonding or antibonding?
For each of these contour representations of molecular orbitals, identify: The atomic orbitals (s or p) used to construct the MO
For each of these contour representations of molecular orbitals, identify: The type of MO (sigma or pi)
For each of these contour representations of molecular orbitals, identify: Whether the MO is bonding or antibonding?
Sketch each molecular orbital. Choose the appropriate labels to their perspective targets.δ2sδ*2sδ2pπ*2pδ*2pπ2p
Which of these molecular electron configurations describe an excited state? Check all that apply.a. (σ1s)2(σ1s*)2(σ2s)2(σ2s*)2(σ2p)2(π2p)4b. (σ1s)2(σ1s*)2(π2p)1c. (σ1s)2(σ1s*)2(σ2s)2(σ2s*)2(σ2p)2(σ2p*)1d. (σ1s)2(σ1s*)2(σ2s)1(σ2s*)1
True or false: Boron contains 2s 22p1 valence electrons, so only one p orbital is needed to form molecular orbitals.
The molecular orbitals depicted below are derived from  n = 2 atomic orbitals. Give the orbital designations.
The molecular orbitals depicted below are derived from  n = 2 atomic orbitals. Which is highest in energy?
The molecular orbitals depicted below are derived from  n = 2 atomic orbitals. Which is lowest in energy?
Consider the following electron configuration:(σ3s)2 (σ3s*)2 (σ3p)2 (π3p)4 (π3p*)4Give four species that, in theory, would have this electron configuration.
Sketch the molecular orbital and label its type (σ or π; bonding or antibonding) that would be formed when the following atomic orbitals overlap. Explain your labels.
Sketch the molecular orbital and label its type (σ or π; bonding or antibonding) that would be formed when the following atomic orbitals overlap. Explain your labels.
Sketch the molecular orbital and label its type (σ or π; bonding or antibonding) that would be formed when the following atomic orbitals overlap. Explain your labels.
Sketch the molecular orbital and label its type (σ or π; bonding or antibonding) that would be formed when the following atomic orbitals overlap. Explain your labels.
Sketch the distribution of electron density in the bonding and antibonding molecular orbitals formed from two s orbitals and from two p orbitals.
How the following similar, and how do they differ?(a) σ molecular orbitals and π molecular orbitals
How the following similar, and how do they differ?(b) ψ for an atomic orbital and ψ for a molecular orbital
How the following similar, and how do they differ?(c) bonding orbitals and antibonding orbitals
If molecular orbitals are created by combining five atomic orbitals from atom A and five atomic orbitals from atom B combine, how many molecular orbitals will result?
Can a molecule with an odd number of electrons ever be diamagnetic? Explain why or why not.
Can a molecule with an even number of electrons ever be paramagnetic? Explain why or why not.
Why are bonding molecular orbitals lower in energy than the parent atomic orbitals?
How many electrons does it take to fill (b) a π antibonding MO;
How many electrons does it take to fill (a) a σ bonding MO;
How many electrons does it take to fill (c) the MOs formed from combination of the 1s orbitals of two atoms?
How many electrons does it take to fill (a) the MOs formed from combination of the 2p orbitals of two atoms;
How many electrons does it take to fill (b) a σ*2p MO;
How many electrons does it take to fill (c) the MOs formed from combination of the 2s orbitals of two atoms?