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- a) Using only the valence atomic orbitals of a hydrogen atom and a fluorine atom, and following the model of Figure 9.46, how many MOs would you expect for the HF molecule?
Problem 110
Problem 110b
(b) How many of the MOs from part (a) would be occupied by electrons?
Problem 110c
(c) It turns out that the difference in energies between the valence atomic orbitals of H and F are sufficiently different that we can neglect the interaction of the 1s orbital of hydrogen with the 2s orbital of fluorine.
The 1s orbital of hydrogen will mix only with one 2p orbital of fluorine. Draw pictures showing the proper orientation of all three 2p orbitals on F interacting with a 1s orbital on H. Which of the 2p orbitals can actually make a bond with a 1s orbital, assuming that the atoms lie on the z-axis?
Problem 112b
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. (b) Assuming this electronic transition corresponds to the HOMO-LUMO transition, what is the LUMO in ethylene?
- A compound composed of 6.7% H, 40.0% C, and 53.3% O has a molar mass of approximately 60 g>mol. (c) What is the geometry and hybridization of the C atom that is bonded to 2 O atoms?
Problem 113
- Sulfur tetrafluoride (SF₄) reacts slowly with O₂ to form sulfur tetrafluoride monoxide (OSF₄) according to the following unbalanced reaction: SF₄(g) + O₂(g) → OSF₄(g). The O atom and the four F atoms in OSF₄ are bonded to a central S atom. (d) Determine the electron-domain geometry of OSF₄, and write two possible molecular geometries for the molecule based on this electron-domain geometry. (e) For each of the molecules you drew in part (d), state how many fluorines are equatorial and how many are axial.
Problem 114
Problem 114a
Sulfur tetrafluoride 1SF42 reacts slowly with O2 to form sulfur tetrafluoride monoxide 1OSF42 according to the following unbalanced reaction: SF41g2 + O21g2¡OSF41g2 The O atom and the four F atoms in OSF4 are bonded to a central S atom. (a) Balance the equation.
Problem 114b
Sulfur tetrafluoride (SF4) reacts slowly with O2 to form sulfur tetrafluoride monoxide (OSF4) according to the following unbalanced reaction: SF4(g) + O2(g) → OSF4(g) The O atom and the four F atoms in OSF4 are bonded to a central S atom. (b) Write a Lewis structure of OSF4 in which the formal charges of all atoms are zero.
Problem 114c
Sulfur tetrafluoride (SF4) reacts slowly with O2 to form sulfur tetrafluoride monoxide (OSF4) according to the following unbalanced reaction: SF4(g) + O2(g) → OSF4(g) The O atom and the four F atoms in OSF4 are bonded to a central S atom. (c) Use average bond enthalpies (Table 8.3) to estimate the enthalpy of the reaction. Is it endothermic or exothermic?
Problem 114e
Sulfur tetrafluoride 1SF42 reacts slowly with O2 to form sulfur
tetrafluoride monoxide 1OSF42 according to the following
unbalanced reaction:
SF41g2 + O21g2¡OSF41g2
The O atom and the four F atoms in OSF4 are bonded to a
central S atom.
(e) For each of the molecules you drew in part (d), state how many
fluorines are equatorial and how many are axial.
- The phosphorus trihalides 1PX32 show the following variation in the bond angle X¬P¬X: PF3, 96.3°; PCl3, 100.3°; PBr3, 101.0°; PI3, 102.0°. The trend is generally attributed to the change in the electronegativity of the halogen. (b) What is the general trend in the X¬P¬X angle as the halide electronegativity increases?
Problem 115
- (b) Make a similar comparison of nitrogen–nitrogen bonds. What do you observe? (d) Propose a reason for the large difference in your observations of parts (a) and (b).
Problem 117
- (b) Determine ΔH for the atomization of naphthalene using Hess’s law and the data in Appendix C. (ΔHf° of solid naphthalene is 77.1 kJ/mol and the molar heat of sublimation of naphthalene is 72.9 kJ/mol.)
Problem 118
- Many compounds of the transition-metal elements contain direct bonds between metal atoms. We will assume that the z-axis is defined as the metal–metal bond axis. (d) Sketch the energylevel diagram for the Sc2 molecule, assuming that only the 3d orbital from part (a) is important.
Problem 119
- The organic molecules shown here are derivatives of benzene in which six-membered rings are 'fused' at the edges of the hexagons.
Problem 120
(e) 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 on orbitals and energy.
Problem 120b
The organic molecules shown here are derivatives of benzene in which six-membered rings are 'fused' at the edges of the hexagons.
(b) Suppose you are given a sample of one of the compounds. Could combustion analysis be used to determine unambiguously which of the three it is?
Problem 122a
Methyl isocyanate, CH3NCO, was made infamous in 1984 when an accidental leakage of this compound from a storage tank in Bhopal, India, resulted in the deaths of about 3800 people and severe and lasting injury to many thousands more. (a) Draw a Lewis structure for methyl isocyanate.