Chapter 11

According to VSEPR theory, what determines the geometry of a molecule?

Name and sketch the five basic electron geometries, and state the number of electron groups corresponding to each. What constitutes an electron group?

Explain the difference between electron geometry and molecular geometry. Under what circumstances are they not the same?

Give the correct electron and molecular geometries that correspond to each set of electron groups around the central atom of a molecule. a. four electron groups overall; three bonding groups and one lone pair b. four electron groups overall; two bonding groups and two lone pairs c. five electron groups overall; four bonding groups and one lone pair d. five electron groups overall; three bonding groups and two lone pairs e. five electron groups overall; two bonding groups and three lone pairs f. six electron groups overall; five bonding groups and one lone pair g. six electron groups overall; four bonding groups and two lone pairs

How do you determine whether a molecule is polar? Why is polarity important?

In valence bond theory, what determines the geometry of a molecule?

What is hybridization? Why is hybridization necessary in valence bond theory?

How is the mumber of hybrid orbitals related to the number of standard atomic orbitals that are hybridized?

Sketch each set of hybrid orbitals. a. \(s p\) b. \(s p^{2}\) c. \(s p^{3}\) d. \(s p^{3} d\) e. \(s p^{3} d^{2}\)

Name the hybridization scheme that corresponds to each electron geometry. a. linear b. trigonal planar c. tetrahedral d. trigonal bipyramidal e. octahedral

What is a chemical bond according to MO theory?

Explain the difference between hybrid atomic orbitals in valence bond theory and LCAO molecular orbitals in MO theory.

What is an antibonding molecular orbital?

What is the role of wave interference in determining whether a molecular orbital is bonding or antibonding?

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?

Draw an energy diagram for the molecular orbitals of period 2 diatomic molecules. Show the difference in ordering for \(\mathrm{B}_{2}, \mathrm{C}_{2}\) and \(\mathrm{N}_{2}\) compared to \(\mathrm{O}_{2}, \mathrm{~F}_{2},\) and \(\mathrm{Ne}_{2}\)

Explain the difference between a paramagnetic species and a diamagnetic one.

When applying MO 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? How is the shape of the resultant molecular orbitals related to the shape of the atomic orbitals?

In MO theory, what is a nonbonding orbital?

Write a short paragraph describing chemical bonding according to the Lewis model, valence bond theory, and MO theory. Indicate how the theories differ in their description of a chemical bond and describe the strengths and weaknesses of each theory. Which theory is correct?

A molecule with the formula \(A B_{3}\) has a trigonal pyramidal geometry. How many electron groups are on the central atom (A)?

A molecule with the formula \(A B_{3}\) has a trigonal planar geometry. How many electron groups are on the central atom?

Determine the electron geometry, molecular geometry, and idealized bond angles for each molecule. In which cases do you expect deviations from the idealized bond angle? a. \(\mathrm{PF}_{3}\) b. \(\mathrm{SBr}_{2}\) c. CHCl \(_{3}\) d. \(\mathrm{CS}_{2}\)

Which species has the smaller bond angle, \(\mathrm{H}_{3} \mathrm{O}^{+}\) or \(\mathrm{H}_{2} \mathrm{O}\). Explain.

Determine the molecular geometry about each interior atom and sketch each molecule. a. \(\mathrm{C}_{2} \mathrm{H}_{2}\) (skeletal structure \(\mathrm{HCCH}\) ) b. \(\mathrm{C}_{2} \mathrm{H}_{4}\) (skeletal structure \(\mathrm{H}_{2} \mathrm{CCH}_{2}\) ) c. \(\mathrm{C}_{2} \mathrm{H}_{6}\) (skeletal structure \(\mathrm{H}_{3} \mathrm{CCH}_{3}\) )

Determine the molecular geometry about each interior atom and sketch each molecule. a. \(\mathrm{N}_{2}\) b. \(\mathrm{N}_{2} \mathrm{H}_{2}\) (skeletal structure HNNH) c. \(\mathrm{N}_{2} \mathrm{H}_{4}\) (skeletal structure \(\mathrm{H}_{2} \mathrm{NNH}_{2}\) )

Determine the geometry about each interior atom in each molecule and sketch the molecule. (Skeletal structure is indicated in parentheses.) a. \(\mathrm{CH}_{3} \mathrm{OH}\left(\mathrm{H}_{3} \mathrm{COH}\right)\) b. \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\left(\mathrm{H}_{3} \mathrm{COCH}_{3}\right)\) c. \(\mathrm{H}_{2} \mathrm{O}_{2}(\mathrm{HOOH})\)

Determine the geometry about each interior atom in each molecule and sketch the molecule. (Skeletal structure is indicated in parentheses.) a. \(\mathrm{CH}_{3} \mathrm{NH}_{2}\left(\mathrm{H}_{3} \mathrm{CNH}_{2}\right)\) b. \(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{CH}_{3}\left(\mathrm{H}_{3} \mathrm{CCOOCH}_{3}\right.\) one \(\mathrm{O}\) atom attached to \(2 \mathrm{nd} \mathrm{C}\) atom; the other \(\mathrm{O}\) atom is bonded to the \(2 \mathrm{nd}\) and \(3 \mathrm{rd}\) C atom \()\) c. \(\mathrm{NH}_{2} \mathrm{CO}_{2} \mathrm{H}\left(\mathrm{H}_{2} \mathrm{NCOOH}\right.\) both \(\mathrm{O}\) atoms attached to \(\mathrm{C}\) )

Explain why \(\mathrm{CO}_{2}\) and \(\mathrm{CCl}_{4}\) are both nonpolar, even though they contain polar bonds.

\(\mathrm{CH}_{3} \mathrm{~F}\) is a polar molecule, even though the tetrahedral geometry often leads to nonpolar molecules. Explain.

Determine whether each molecule is polar or nonpolar. a. \(\mathrm{SiCl}_{4}\) b. \(\mathrm{CF}_{2} \mathrm{Cl}_{2}\) c. SeF d. IF \(_{5}\)

The valence electron configurations of several atoms are shown here. How many bonds can each atom make without hybridization? a. Be \(2 s^{2}\) b. \(\mathrm{P} 3 \mathrm{~s}^{2} 3 p^{3}\) c. F \(2 s^{2} 2 p^{5}\)

The valence electron configurations of several atoms are shown here. How many bonds can each atom make without hybridization? a. \(\mathrm{B} 2 \mathrm{~s}^{2} 2 p^{1}\) b. \(\mathrm{N} 2 s^{2} 2 p^{3}\) c. \(\mathrm{O} 2 \mathrm{~s}^{2} 2 p^{4}\)

Write orbital diagrams (boxes with arrows in them) to represent the electron configurations-without hybridization-for all the atoms in \(\mathrm{PH}_{3}\). Circle the electrons involved in bonding. Draw a three-dimensional sketch of the molecule and show orbital overlap. What bond angle do you expect from the unhybridized orbitals? How well does valence bond theory agree with the experimentally measured bond angle of \(93.3^{\circ} ?\)

Write orbital diagrams (boxes with arrows in them) to represent the electron configuration of carbon before and after \(s p^{3}\) hybridization.

Which hybridization scheme allows the formation of at least one \(\pi\) bond? $$ s p^{3}, s p^{2}, s p^{3} d^{2} $$

Which hybridization scheme allows the central atom to form more than four bonds? $$ s p^{3}, s p^{3} d, s p^{2} $$

Sketch the bonding molecular orbital that results from the linear combination of two \(1 \mathrm{~s}\) orbitals. Indicate the region where interference occurs and state the kind of interference (constructive or destructive).

Sketch the antibonding molecular orbital that results from the linear combination of two 1 s orbitals. Indicate the region where interference occurs and state the kind of interference (constructive or destructive).

Sketch the bonding and antibonding molecular orbitals that result from linear combinations of the \(2 p_{x}\) atomic orbitals in a homonuclear diatomic molecule. (The \(2 p_{x}\) orbitals are those whose lobes are oriented along the bonding axis.)

Sketch the bonding and antibonding molecular orbitals that result from linear combinations of the \(2 p_{z}\) atomic orbitals in a homonuclear diatomic molecule. (The \(2 p_{z}\) orbitals are those whose lobes are oriented perpendicular to the bonding axis.)

Using the molecular orbital energy ordering for second-row homonuclear diatomic molecules in which the \(\pi_{2 p}\) orbitals lie at lower energy than the \(\sigma_{2 p}\), 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?

Use MO theory to predict if each molecule or ion exists in a relatively stable form. a. \(\mathrm{H}_{2}^{2-}\) b. \(\mathrm{Ne}_{2}\) c. \(\mathrm{He}_{2}^{2+}\) d. \(\mathrm{F}_{2}^{2-}\)

Use MO theory to predict if each molecule or ion exists in a relatively stable form. a. \(\mathrm{C}_{2}^{2+}\) b. \(L i_{2}\) c. \(\mathrm{Be}_{2}^{2+}\) d. \(\mathrm{Li}_{2}^{2-}\)

For each compound, draw the Lewis structure, determine the geometry using VSEPR theory, determine whether the molecule is polar, identify the hybridization of all interior atoms, and make a sketch of the molecule, according to valence bond theory, showing orbital overlap. a. IF \(_{5}\) b. \(\mathrm{CH}_{2} \mathrm{CHCH}_{3}\) c. \(\mathrm{CH}_{3} \mathrm{SH}\)

The compound \(\mathrm{C}_{3} \mathrm{H}_{4}\) has two double bonds. Describe its bonding and geometry, using a valence bond approach.

Draw the structures of two compounds that have the composition \(\mathrm{CH}_{3} \mathrm{NO}_{2}\) and have all three \(\mathrm{H}\) atoms bonded to the \(\mathrm{C}\). Predict which compound has the larger ONO bond angle.

How many types of hybrid orbitals do we use to describe each molecule? a. \(\mathrm{N}_{2} \mathrm{O}_{5}\) b. \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NO}\) (four \(\mathrm{C}-\mathrm{H}\) bonds and one \(\mathrm{O}-\mathrm{H}\) bond \()\) c. BrCN (no formal charges)

In VSEPR theory, which uses the Lewis model to determine molecular geometry, the trend of decreasing bond angles in \(\mathrm{CH}_{4}, \mathrm{NH}_{3},\) and \(\mathrm{H}_{2} \mathrm{O}\) is accounted for by the greater repulsion of lone pair electrons compared to bonding pair electrons. How would this trend be accounted for in valence bond theory?

The ion \(\mathrm{CH}_{5}^{+}\) can form under very special high-energy conditions in the vapor phase in a mass spectrometer. Propose a hybridization for the carbon atom and predict the geometry.