The molecular model of nicotme (a stimulant) is shown

Problem 121AP The bond length of the transient diatomic molecule CF is 129.1 pm. and that of the molecular ion CF+ is 117.3 pm. Using molecular orbital theory, explain why the CF bond shortens with the loss of an electron.

Problem 1QP How is the geometry of a molecule defined, and why is the study of molecuiar geometry important?

Problem 1VC How is a sigma bond different from a pi bond? (a) A sigma bond is a bonding molecular orbital; a pi bond is an antibonding molecular orbital. ________________ (b) A sigma bond is a single bond, whereas a pi bond is a double bond. ________________ (c) The electron density in a sigma bond lies along the internuclear axis; that of a pi bond does not.

Problem 2VC Pi bonds form when ______ atomic orbitals on _______ atom(s) overlap. (a) perpendicular, adjacent ________________ (b) parallel, adjacent ________________ (c) parallel, the same

Problem 2QP Sketch the shape of a linear triatomic molecule, a trigonal planar molecule containing four atoms, a tetrahedral molecule, a trigonal bipyramidal molecule, and an octahedral molecule. Give the bond angles in each case.

How many atoms are directly bonded to the central atom in a tetrahedral molecule, a trigonal bipyramidal molecule, and an octahedral molecule?

Problem 3VC Formation of two pi bonds requires the combination of _________ atomic orbitals. (a) two ________________ (b) four ________________ (c) six

Discuss the basic features of the VSEPR model. Explain why the magnitude of repulsion decreases in the following order: lone pair–lone pair > lone pair–bonding pair > bonding pair–bonding pair.

Problem 5QP In the trigonal bipyramidal arrangement, why does a lone pair occupy an equatorial position rather than an axial position?

Predict the geometry of the following molecules and ion using the VSEPR model: \(\text { (a) } \mathrm{CH}_{3} \mathrm{I} \text {, (b) } \mathrm{ClF}_{3} \text {, (c) } \mathrm{H}_{2} \mathrm{~S} \text {, }\)\(\text { (d) } \mathrm{SO}_{3} \text {, (e) } \mathrm{SO}_{4}^{2-} \text {. }\)

Why are there no pi bonds in ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{6}\right)\)? (a) The remaining unhybridized p orbitals do not contain any electrons. (b) There are no unhybridized p orbitals remaining on either C atom. (c) The remaining unhybridized p orbitals are not parallel to each other.

Problem 7QP Predict the geometry of the following moleculcs and ion using the VSEPR model: (a) CBr4, (b) BCl3, (c) NF3, (d) H2Se, (e)

Problem 8QP Predict the geometries of the following species: (a) AlCl3, (b) , (c) ZnCl2 (d) .

Problem 9QP Predict the geometries of the following species using the VSEPR method: (a) PCl3, (b) CHCl3, (c) SiH4, (d) TeCl4.

Problem 10QP Predict the geometries of the following ions: (a) , (b) , (c) , (d) , (e) , (f) , (g) , (h) H3O+, (i) .

Predict the geometry of the following molecules using the VSEPR method: (a) \(\mathrm{HgBr}_2\), (b) \(\mathrm{N}_2 \mathrm{O}\) (arrangement of atoms is NNO), (c) \(\mathrm{SCN}^{-}\) (arrangement of atoms is SCN).

Problem 12QP Which of the following species are tetrahedral: SiCl4, SeF4, XeF4, CI4,

Problem 13QP Describe the geometry around each of the three ccntral atoms in the CH3COOH molecule.

Describe the geometry about each of the central atoms in ethanolamine, shown here.

Problem 15QP Which of the following shows a deviation from ideal bond angles that is not possible for an ABx molecule? Explain.

Problem 16QP Explain why an atom cannot have a permanent dipole moment.

The bonds in beryllium hydride \(\left(\mathrm{BeH}_{2}\right)\) molecules are polar, and yet the dipole moment of the molecule is zero. Explain.

Problem 19QP Determine whether (a) BrF5, (b) ClF3, and (c) BCl3, are polar.

Problem 18QP Determine whether (a) NBr3, (b) OCS, and (c) XeF4 are polar.

Which of the molecules shown is polar?

Problem 21QP Which of the molecules shown is polar?

Determine which molecule will condense to a liquid at the higher temperature and explain why: \(\mathrm{NH}_3\) or \(\mathrm{CH}_4\).

Problem 23QP Determine which molecule will condense to a liquid at the higher temperature and explain why: SiH4 or PH3.

Problem 24QP What is valence bond theory? How does it differ from the Lewis concept of chcmical bonding?

Use valence bond theory to explain the bonding in \(\mathrm{Cl}_{2}\) and HCl. Show how the atomic orbitals overlap when a bond is formed.

Problem 26QP According to valence bond theory, how many bonds would you expect each of the following atoms (in the ground state) to form: Be, C?

According to valence bond theory, how many bonds would you expect each of the following atoms (in the ground state) to form: P, S?

Problem 29QP For which molecule(s) can we not use valence bond theory to explain the bonding: N2. BF3 (F—B—F bond angles = 120°). HI? Explain.

What is the hybridization of atomic orbitals? Why do we never refer to isolated atoms as hybridized?

For which molecule(s) can we not use valence bond theory to explain the bonding: \(\mathrm{BeCl}_2(\mathrm{Cl}-\mathrm{Be}-\mathrm{Cl}\) bond angle \(=180^{\circ})\), \(\mathrm{Br}_2, \mathrm{SF}_6\)\((\mathrm{~F}-\mathrm{S}-\mathrm{F}\) bond angles \(=90^{\circ}\) and \(180^{\circ}\) )? Explain.

Problem 31QP Is it possible for two 2p orbitals on an atom to combine to give two hybrid orbitals? Explain.

Problem 32QP Determine the hybridization of the central atom in a molecule with the following molecular geometries: (a) tetrahedral, (b) trigonal planar, (c) trigonal bipyramidal, (d) linear, (e) octahedral.

What is the angle between any two of the following two hybrid orbitals on an atom: \(\text { (a) } s p \text {, (b) } s p^{2} \text {, (c) } s p^{3}\) ? Explain why the answer to this question would be more complicated for \(s p^{3} d \text { and } s p^{3} d^{2}\) hybrid orbitals.

Problem 34QP Describe the bonding scheme of the AsH3 molecule in terms of hybridization.

Problem 35QP What is the hybridization state of Si (a) in SiH4 and (b) in H3Si–SiH3?

Problem 36QP What hybrid orbitals are used by nitrogen atoms in the following species: (a) NH3, (b) H2N–NH2, (c)

Problem 37QP Describe the hybridization of phosphorus in PF5.

Describe the change in hybridization (if any) of the \(\mathrm{Al}\) atom when aluminum trichloride, \(\mathrm{AlCl}_3\), interacts with a chloride ion to form the tetrachloroaluminate ion, \(\mathrm{AlCl}_4^{-}\). (Hint: Start by drawing Lewis structures.)

Problem 39QP Describe the changes in hybridization (if any) of the B and N atoms as a result of the formation of F3B—NH3 from BF3, and NH3. (Hint: Start by drawing Lewis structures.)

Problem 40QP How would you distinguish between a sigma bond and a pi bond?

Problem 42QP What are the hybrid orbitals of the carbon atoms in the follow ing molecules? (a) H3C–CH3 ________________ (b) H3C–Ch=CH2 ________________ (c) CH3-C=C–CH2OH ________________ (d) CH3CH=0 ________________ (e) CH3COOH

Problem 41QP Which of the following pairs of atomic orbitals of adjacent nuclei can overlap to form a sigma bond? Which overlap to form a pi bond? Which cannot overlap (no bond)? Consider the.x axis to be the internuclear axis, that is, the line joining the nuclei of the two atoms, (a) 1s and 1s, (b) 1s and 2px, (c) 2px and 2py, (d) 3py and 3py, (e) 2px and 2px, (f) 1s and 2s.

Problem 44QP The allene molecule (H2C=C=CH2) is linear (the three C atoms lie on a straight line). What are the hybridization states of the carbon atoms? Draw diagrams to show the formation of sigma bonds and pi bonds in allene.

Problem 43QP Specify which hybrid orbitals are used by carbon atoms in the following species: (a) CO, (b) CO2, (c) CN–.

Problem 45QP What is the hybridization of the central N atom in the azide ion (The arrangement of atoms is NNN.)

How many pi bonds and sigma bonds are there in the tetracyanoethylene molecule?

Problem 46QP How many sigma bonds and pi bonds are there in each of the following molecules?

Problem 50QP What is molecular orbital theory? How does it differ from valence bond theory?

Problem 49QP Benzo(a)pyrene is a potent carcinogen found in coal cigarette smoke. Determine the number of sigma and pi bonds in the molecule.

Problem 51QP Define the following terms: bonding molecular orbital, antibonding molecular orbital, pi molecular orbital, sigma molecular orbital.

Tryptophan is one of the 20 amino acids in the human body. Describe the hybridization of the C atoms and the N atoms, and determine the number of sigma and pi bonds in the molecule.

Problem 52QP Sketch the shapes of the follow ing molecular orbitals: How do their energies compare?

Problem 53QP Explain the significance of bond order. Can bond order be used for quantitative comparisons of the strengths of chemical bonds?

Problem 54QP Using molecular orbital theory, explain the changes that occur in the H—H internuclear distance as the molecule H2, is ionized first to and then to .

Problem 56QP Draw a molecular orbital energy level diagram for each of the following species: He2, HHe, Compare their relative stabilities in terms of bond orders. (Treat HHe as a diatomic molecule with three electrons.)

The formation of \(\mathrm{H}_2\) from two \(\mathrm{H}\) atoms is an energetically favorable process. Yet, statistically there is less than a 100 percent chance that any two \(\mathrm{H}\) atoms will undergo the reaction. Apart from energy considerations, how would you account for this observation based on the electron spins in the two \(\mathrm{H}\) atoms?

Problem 57QP Arrange the following species in order of increasing stability: Li2, Justify your choice w ith a molecular orbital energy level diagram.

Problem 58QP It has long been predicted that Be, could not exist because the molecule would not be stable. However, in 2009, the existence of Be2, was confirmed by spectroscopy. Use molecular orbital theory to explain why the Be2 molecule was predicted not to exist.

Problem 60QP Acetylene (C2H2) has a tendency to lose two protons (H+) and form the carbide ion which is present in a number of ionic compounds, such as CaC2 and MgC2. Describe the bonding scheme in the ion in terms of molecular orbital theory. Compare the bond order in with that in C2.

Problem 59QP Which of these species has a longer bond. B2 or Explain in terms of molecular orbital theory.

Problem 61QP Compare the Lewis and molecular orbital treatments of the oxygen molecule.

Problem 62QP Explain why the bond order of N2 is greater than that of but the bond order of O2 is less than that of

Problem 64QP Use molecular orbital theory to compare the relative stabilities of F2 and

Problem 65QP A single bond is almost always a sigma bond, and a double bond is almost always made up of a sigma bond and a pi bond. There are very few exceptions to this rule. Show that the B2 and C2 molecules are examples of the exceptions.

Problem 63QP Compare the relative bond orders of the fallowing species and indicate their magnetic properties (that is, diamagnetic or paramagnetic): (superoxide ion), (peroxide ion).

Problem 67QP Given that BeO is diamagnetic, use a molecular orbital diagram to determine whether the orbitals are ordered like those of Be2 or those of O2.

Problem 66QP Draw the molecular orbital diagram for the cyanide ion (CN?). (Assume the ordering of moleculer orbitals to be like that in N2.) Write the electron configuration of the cyanide ion (CN?).

Problem 69QP In Chapter 8 we saw that the resonance concept is useful for dealing with species such as the benzene molecule and the carbonate ion. How does molecular orbital theory deal with these species?

Problem 70QP Both ethylene (C2H4) and benzene (C6H6) contain the C=C bond, yet benzene is more stable in that it does not combine readily with other molecules—whereas ethylene does. Explain this difference in the chemical properties of these two species.

How does a delocalized molecular orbital differ from a molecular orbital such as that found in \(\mathrm{H}_2\) or \(\mathrm{C}_2 \mathrm{H}_4\) ? What do you think are the minimum conditions (for example, number of atoms and types of orbitals) for forming a delocalized molecular orbital?

Nitryl fluoride (FNO2 ) is used in rocket propellants. The fluorine and oxygen atoms are bonded to the nitrogen atom. (a) Draw a Lewis structure for \(\mathrm{FNO_2}\). (b) Indicate the hybridization of the nitrogen atom. (c) Describe the bonding in terms of molecular orbital theory. Where would you expect delocalized molecular orbitals to form?

Problem 74QP Describe the bonding in the nitrate ion in terms of delocalized molecular orbitals.

Problem 71QP Explain why the symbol on the left is a better representation of benzene molecules than that on the right.

Determine which of these molecules has a more delocalized orbital, and justify your choice. (Hint: Both molecules contain two benzene rings. In naphthalene, the two rings are fused together. In biphenyl, the two rings are joined by a single bond around which the two rings can rotate.)

Problem 75QP What is the state of hybridization of the ccntral O atom in O3? Describe the bonding in O3 in terms of delocalized molecular orbitals.

Problem 76AP Which of the following species is not likely to have a tetrahedral shape:

Draw the Lewis structure of mercury(II) bromide. Is this molecule linear or bent? How would you establish its geometry?

Problem 80AP Antimony pentafluoride (SbF5) reacts with XeF4 and XeF6 to form ionic compounds, and Describe the geometries of the cations and anions in these two compounds.

Problem 79AP Predict the geometry of sulfur dichloride (SCl2) and the hybridization of the sulfur atom.

Problem 78AP Although both carbon and silicon are in Group 4A, very few Si=Si bonds are known. Account for the instability of silicon-to-silicon double bonds in general. (Hint: Compare the atomic radii of C and Si in Figure 7.6. What effect would the larger size have on pi bond formation?)

Problem 82AP The molecular model of nicotme (a stimulant) is shown here, (a) Write the molecular formula of the compound, (b) What is the hybridization of each C and N atom? (c) Describe the geometry about each C and N atom.

The molecular model of vitamin C is shown here. (a) Write the molecular formula of the compound. (b) What is the hybridization of each C and O atom? (c) Describe the geometry about each C and O atom.

Problem 83AP Predict the bond angles for the following molecules: (a) BeCl2, (b) BCl3, (c) CCl4, (d) CH3Cl, (e) Hg2Cl2 (arrangement of atoms: ClHgHgCl), (f) SnCl2, (g) H2O2, (h) SnH4.

Problem 84AP The germanium pentafluoride anion ( ) has been observed as part of an ionic compound with cesium at low temperatures. The anion is formed by the interaction of GeF4 with F?. Which figure best illustrates the change in molecular geometry around Ge in the transformation from GeF4 to ?

The disulfide bond,\(-\mathrm{S}-\mathrm{S}-\), plays an important role in determining the three-dimensional structure of proteins. Describe the nature of the bond and the hybridization of the S atoms.

Problem 88AP Draw Lewis structures and give the other information requested for the following: (a) SO3. Polar or nonpolar molecule? (b) PF3. Polar or nonpolar? (c) F3SiH. Polar or nonpolar? (d) Shape: planar or pyramidal? (e) Br2CH2. Polar or nonpolar molecule?

Problem 85AP Draw Lewis structures and give the other information requested for the following molecules: (a) BF3. Shape: planar or nonplanar? (b) Shape: planar or nonplanar? (c) HCN. Polar or nonpolar? (d) OF2. Polar or nonpolar? (c) NO2. Estimate the ONO bond angle.

Problem 86AP Which figure best illustrates the hybridization of arsenic in (a) arsenic pentafluoride (AsF5) and (b) arsenic trifluoride (AsF3)?

Problem 89AP Which of the following molecules are linear: CdBr2?

Problem 90AP Semiconducting materials such as indium phosphide (InP) can be prepared from a single-source precursor like (CH3)3In—P(CH3)3. Which pair of figures best illustrates the hybridization of In and P, respectively, in (CH3)3In—P(CH3)3?

Problem 92AP Cyclopropane (C3H6) has the shape of a triangle in which a C atom is bonded to two H atoms and two other C atoms at each corner. Cubane (C8H8) has the shape of a cube in which a C atom is bonded to one H atom and three other C atoms at each corner, (a) Draw Lewis structures of these molecules. (b) Compare the CCC angles in these molecules with those predicted for an sp3-hybridized C atom, (c) Would you expect these molecules to be easy to make?

The \(\mathrm{N}_2 \mathrm{~F}_2\) molecule can exist in either of the following two forms: (a) What is the hybridization of N in each case? (b) Identify each structure as polar or nonpolar.

Problem 95AP So-called greenhouse gases, which contribute to global warming, have a dipole moment or can be bent or distorted during molecular vibration into shapes that have a temporary dipole moment. Which of the following gases are greenhouse gases: N2, O2, O3, CO, CO2, NO2, N2O, CH4, CFCl3?

Problem 96AP Carbon suboxide (C3O2) is a colorless pungent-smelling gas. Does this molecule possess a dipole moment? Explain.

Problem 94AP Does the following molecule have a dipole moment? Explain.

Problem 93AP The compound 1,2-dichlorocthane (C2H4Cl2) is nonpolar, while cis-dichloroethylcnc (C2H2Cl2) has a dipole moment: The reason for the difference is that groups conncctcd by a single bond can rotate with respect to each other, but no rotation occurs when a double bond connects the groups. On the basis of bonding considerations, explain why rotation occurs in 1,2-dichlorocthanc but not in cis-dichloroethylene.

Problem 97AP The compound 3?-azido-3?-dcoxythymidine, commonly known as AZT, is one of the drags used to treat AIDS. What are the hybridization states of the C and N atoms in this molecule?

Problem 102AP The stable allotropic form of phosphorus is P4, in which each P atom is bonded to three other P atoms. Draw a Lewis structure of this molecule and describe its geometry. At high temperatures, P4 dissociates to form P2 molecules containing a P=P bond. Explain why P4 is more stable than P2.

Problem 103AP The BO+ ion is paramagnetic. Determine (a) whether the order of molecular-orbital energies is like that in B, or in O2; (b) the bond order; and (c) the number of unpaired electrons in the ion.

Problem 99AP The amino acid selenocysteine is one of the components of selenoproteins, more than 20 of which have been identified so far in human cells. In the structure of this interesting amino acid, how many of each type of hybrid orbital illustrated here are present?

Problem 104AP Use molecular orbital theory to explain the bonding in the azide ion (The arrangement of atoms is NNN.)

Problem 107AP Greenhouse gases absorb (and trap) outgoing infrared radiation (heat) from Earth and contribute to global warming. A molecule of a greenhouse gas either possesses a permanent dipole moment or has a changing dipole moment during its vibrational motions. Consider three of the vibrational modes of carbon dioxide where the arrows indicate the movement of the atoms. (During a complete cyclc of vibration, the atoms move toward one extreme position and then reverse their direction to the other extreme position.) Which of the preceding vibrations are responsible for CO2 behaving as a greenhouse gas?

Problem 101AP What is the hybridization of C and of N in this molecule?

Which best illustrates the change in geometry about the central S atom when \(\mathrm{SO}_{3}\) gains two electrons to become the \(\mathrm{SO}_{3}^{2-}\) ion?

Problem 106AP Draw three Lewis structures for compounds with the formula C2H2F2. Indicate which of the compounds are polar.

Problem 98AP The following molecules (AX4Y2) all have an octahedral geometry. Group the molecules that are equivalent to each other.

Problem 108AP Aluminum trichloride (AlCl3) is an electron-deficient molecule. It has a tendency to form a dimer (a molecule made up of two AlCl3 units): (a) Draw a Lewis structure for the dimer. (b) Describe the hybridization state of Al in AlCl3 and Al2Cl6. (c) Sketch the geometry of the dimer. (d) Do these molecules possess a dipole moment?

Problem 110AP The molecule benzyne (C6H4) resembles benzene in that it has a six-membered ring of carbon atoms, but it is far less stable. Draw a Lewis structure of the molecule and account for the molecule’s lack of stability.

Problem 111AP Assume that the third-period element phosphorus fomis a diatomic molecule, P2, in an analogous way as nitrogen does to form N2. (a) Write the electronic configuration for P2. Use [Ne2] to represent the electron configuration for the first two periods. (b) Calculate its bond order, (c) What are its magnetic properties (diamagnctic or paramagnetic)?

Problem 112AP Consider an N2 molecule in its first excited electronic state, that is, when an electron in the highest occupied molecular orbital is promoted to the lowest empty molecular orbital, (a) Identify the molecular orbitals involved, and sketch a diagram to show the transition, (b) Compare the bond order and bond length of with N2. where the asterisk denotes the excited molecule, (c) Is diamagnctic or paramagnetic? (d) When loses its excess energy and converts to the ground state N2, it emits a photon of wavelength 470 nm, which makes up part of the auroras’ lights. Calculate the energy difference between these levels.

Problem 109AP Progesterone is a hormone responsible for female sex characteristics. In the usual shorthand structure, each point where lines meet represents a C atom, and most H atoms are not shown. Draw the complete structure of the molecule, showing all C and H atoms. Indicate which C atoms are sp2- and sp3-hybridized.

Problem 114AP Draw the Lewis structure of ketene (C2H2O) and describe the hybridization states of the C atoms. The molecule does not contain O–H bonds. On separate diagrams, sketch the formation of the sigma and pi bonds.

The Lewis structure for \(\mathrm{O}_2\) is Use molecular orbital theory to show that the structure actually corresponds to an excited state of the oxygen molecule.

Problem 115AP The compound TCDD, or 2,3,7,8-tetrachlorodibenzo-p-dioxin, is highly toxic: It gained considerable notoriety in 2004 when it was implicated in the attempted murder of a Ukrainian politician, (a) Describe its geometry, and state whether the molecule has a dipole moment, (b) How many pi bonds and sigma bonds are there in the molecule?

Problem 116AP Liquid bromine (Br2) and the inter halogen compound ICl have nearly identical molecular masses, yet their boiling points differ by 38°C. Which one has the higher boiling point and why?

Problem 118AP Which of the following ions possess a dipole moment: (a)

Problem 117AP Carbon monoxide (CO) is a poisonous compound due to its ability to bind strongly to Fe2+ in the hemoglobin molecule. The molecular orbitals of CO have the same energy order as those of the N2 molecule. (a) Draw a Lewis structure of CO and assign formal charges. Explain why CO has a rather small dipole moment of 0.12 D. (b) Compare the bond order of CO with that from molecular orbital theory, (c) Which of the atoms (C or O) is more likely to form bonds with the Fe2+ ion in hemoglobin?

Problem 119AP Which of the following geometries has a greater stability for tin(IV) hydride (SnH4)?

Problem 120AP Carbon dioxide has a linear geometry and is nonpolar. Yet we know that the molecule exhibits bending and stretching motions that create a dipole moment. How would you reconcile these seemingly conflicting descriptions of CO2?

Problem 100AP Write the ground-state electron configuration for B2. Is the molecule diamagnetic or paramagnetic?