12. Molecular Shapes & Valence Bond Theory

Which of the following is not consistent with the valence bond theory description of the formation of a chemical bond?

The C2 molecule has a MO diagram similar to N2 (Figure 8.22a). What is the bond order of C2 and is it paramagnetic or diamagnetic? (LO 8.12) (a) Bond order = 2, diamagnetic (b) Bond order = 2, paramagnetic (c) Bond order = 0, paramagnetic (d) Bond order = 3>2, diamagnetic

Consider the H2+ ion. (d) What is the bond order in H2+?

Consider the H2+ ion. (e) Suppose that the ion is excited by light so that an electron moves from a lower-energy to a higher-energy MO. Would you expect the excited-state H2+ ion to be stable or to fall apart?

Draw an MO energy diagram and predict the bond order of Be2+ and Be2- . Do you expect these molecules to exist in the gas phase?

(c) Calculate the bond order in H2-.

Draw an MO energy diagram and predict the bond order of Li2+ and Li2-. Do you expect these molecules to exist in the gas phase?

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the p2p orbitals lie at lower energy than the s2p, draw MO energy diagrams and predict the bond order in a molecule or ion with each number of total valence electrons. Will the molecule or ion be diamagnetic or paramagnetic? d. 9

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the p2p orbitals lie at lower energy than the s2p, draw MO energy diagrams and predict the bond order in a molecule or ion with each number of total valence electrons. Will the molecule or ion be diamagnetic or paramagnetic? c. 8

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the p2p orbitals lie at lower energy than the s2p, draw MO energy diagrams and predict the bond order in a molecule or ion with each number of total valence electrons. Will the molecule or ion be diamagnetic or paramagnetic? a. 4

Explain the following: (c) The O22 + ion has a stronger O—O bond than O2 itself.

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the p2p orbitals lie at higher energy than the s2p, draw MO energy diagrams and predict the bond order in a molecule or ion with each number of total valence electrons. Will the molecule or ion be diamagnetic or paramagnetic? d. 14

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the p2p orbitals lie at higher energy than the s2p, draw MO energy diagrams and predict the bond order in a molecule or ion with each number of total valence electrons. Will the molecule or ion be diamagnetic or paramagnetic? c. 13

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the p2p orbitals lie at higher energy than the s2p, draw MO energy diagrams and predict the bond order in a molecule or ion with each number of total valence electrons. Will the molecule or ion be diamagnetic or paramagnetic? a. 10

Use molecular orbital theory to predict if each molecule or ion exists in a relatively stable form. a. H22 -

Apply molecular orbital theory to predict if each molecule or ion exists in a relatively stable form. a. C22+ b. Li2 c. Be22+ d. Li22-

Using Figures 9.35 and 9.43 as guides, draw the molecular orbital electron configuration for (d) Ne22 +. In each case indicate whether the addition of an electron to the ion would increase or decrease the bond order of the species.

If we assume that the energy-level diagrams for homonuclear diatomic molecules shown in Figure 9.43 can be applied to heteronuclear diatomic molecules and ions, predict the bond order and magnetic behavior of (d) ClF.

If we assume that the energy-level diagrams for homonuclear diatomic molecules shown in Figure 9.43 can be applied to heteronuclear diatomic molecules and ions, predict the bond order and magnetic behavior of (b) NO+.

According to MO theory, which molecule or ion has the shortest bond length? O2, O2- , O22 -

According to MO theory, which molecule or ion has the highest bond energy? O2, O2- , O22 -

According to MO theory, which molecule or ion has the highest bond order? O2, O2- , O22 -

Determine the electron configurations for CN+, CN, and CN-. (a) Which species has the strongest C¬N bond?

Draw an MO energy diagram for CO. (Use the energy ordering of O2.) Predict the bond order and make a sketch of the lowest energy bonding molecular orbital.

Draw an energy diagram for HCl. Predict the bond order and make a sketch of the lowest energy bonding molecular orbital.

Draw a molecular orbital energy diagram for ClF. (Assume that the sp orbitals are lower in energy than the p orbitals.) What is the bond order in ClF?

Draw Lewis structures and MO diagrams for CN+ , CN, and CN- . According to the Lewis model, which species is most stable?

Use the MO energy diagram in Figure 8.22b to describe the bonding in O2+, O2, and O2-. Which of the three is likely to be stable? What is the bond order of each? Which contain unpaired electrons?

The C2 molecule can be represented by an MO diagram similar to that in Figure 8.22a. (b) To increase the bond order of C2, should you add or remove an electron?

Calcium carbide, CaC2, reacts with water to produce acetylene, C2H2, and is sometimes used as a convenient source of that substance. Use the MO energy diagram in Figure 8.22a to describe the bonding in the carbide anion, C22-. What is its bond order?

One of the molecular orbitals of the H2- ion is sketched below: (d) Compared to the H¬H bond in H2, the H¬H bond in H2- is expected to be which of the following: (i) Shorter and stronger, (ii) longer and stronger, (iii) shorter and weaker, (iv) longer and weaker, or (v) the same length and strength?

At high temperatures, sulfur vapor is predominantly in the form of S21g2 molecules. (d) When two electrons are added to S2, the disulfide ion S22- is formed. Is the bond length in S22- likely to be shorter or longer than the bond length in S2? Explain.

Place the following molecules and ions in order from smallest to largest bond order: N22+, He2+, Cl2 H2-, O22-.

Carbon monoxide is produced by incomplete combustion of fossil fuels. (c) What is the bond order of CO? Does this match the bond order predicted by the electron-dot structure?

The energy-level diagram in Figure 9.36 shows that the sideways overlap of a pair of p orbitals produces two molecular orbitals, one bonding and one antibonding. In ethylene there is a pair of electrons in the bonding π 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 p2p to the p*2p molecular orbital. (c) Is the C¬C bond in ethylene stronger or weaker in the excited state than in the ground state? Why?

Use the molecular orbital diagram shown to determine which of the following is most stable.

Use molecular orbital theory to predict whether or not each of the following molecules or ions should exist in a relatively stable form.

Use the molecular orbital diagram shown to determine which of the following is least stable.