Solved: Aluminum trichloride (AlCl3) is an electron-

How is the geometry of a molecule defined and why is the study of molecular geometry important?

Sketch the shape of a linear triatomic molecule, a trigonal planar molecule containing four atoms, a tetrahedral molecule, a trigonal bipyramidal mol ecule, 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?

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

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

The geometry of CH4 could be square planar, with the four H atoms at the corners of a square and the C atom at the center of the square. Sketch this geometry and compare its stability with that of a tetrahedral CH4 molecule

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

Predict the geometries of the following species: (a) AlCl3, (b) ZnCl2, (c) ZnCl4 22

Predict the geometry of the following molecules and ion using the VSEPR model: (a) CBr4, (b) BCl3, (c) NF3, (d) H2Se, (e) NO2 2.

Predict the geometry of the following molecules and ion using the VSEPR model: (a) CH3I, (b) ClF3, (c) H2S, (d) SO3, (e) SO4 22

Predict the geometry of the following molecules using the VSEPR method: (a) HgBr2, (b) N2O (arrangement of atoms is NNO), (c) SCN2 (arrangement of atoms is SCN)

Predict the geometries of the following ions: (a) NH4 1, (b) NH2 2, (c) CO3 22, (d) ICl2 2, (e) ICl4 2, (f) AlH4 2, (g) SnCl5 2, (h) H3O1, (i) BeF4 22.

Describe the geometry around each of the three central atoms in the CH3COOH molecule

Which of the following species are tetrahedral? SiCl4, SeF4, XeF4, CI4, CdCl4

Define dipole moment. What are the units and symbol for dipole moment?

What is the relationship between the dipole moment and the bond moment? How is it possible for a molecule to have bond moments and yet be nonpolar?

Explain why an atom cannot have a permanent dipole moment.

The bonds in beryllium hydride (BeH2) molecules are polar, and yet the dipole moment of the molecule is zero. Explain.

Referring to Table 10.3, arrange the following molecules in order of increasing dipole moment: H2O, H2S, H2Te, H2Se.

The dipole moments of the hydrogen halides decrease from HF to HI (see Table 10.3). Explain this trend.

List the following molecules in order of increasing dipole moment: H2O, CBr4, H2S, HF, NH3, CO2.

Does the molecule OCS have a higher or lower dipole moment than CS2?

Which of the following molecules has a higher dipole moment?

Arrange the following compounds in order of increasing dipole moment: E Cl Cl H Cl A A Cl Cl A A Cl ECl Cl A A Cl E Cl Cl H (a) (b) (c) (d)

What is valence bond theory? How does it differ from the Lewis concept of chemical bonding?

Use valence bond theory to explain the bonding in Cl2 and HCl. Show how the atomic orbitals overlap when a bond is formed

Draw a potential energy curve for the bond formation in F2

(a) What is the hybridization of atomic orbitals? Why is it impossible for an isolated atom to exist in the hybridized state? (b) How does a hybrid orbital differ from a pure atomic orbital? Can two 2p orbitals of an atom hybridize to give two hybridized orbitals?

What is the angle between the following two hybrid orbitals on the same atom? (a) sp and sp hybrid orbitals, (b) sp2 and sp2 hybrid orbitals, (c) sp3 and sp3 hybrid orbitals

How would you distinguish between a sigma bond and a pi bond?

Describe the bonding scheme of the AsH3 molecule in terms of hybridization.

What is the hybridization state of Si in SiH4 and in H3SiSiH3?

Describe the change in hybridization (if any) of the Al atom in the following reaction: AlCl3 1 Cl2 AlCl2 4

Consider the reaction BF3 1 NH3 F3BNH3 Describe the changes in hybridization (if any) of the B and N atoms as a result of this reaction.

What hybrid orbitals are used by nitrogen atoms in the following species? (a) NH3, (b) H2NNH2, (c) NO3 2

What are the hybrid orbitals of the carbon atoms in the following molecules? (a) H3CCH3 (b) H3CCHCH2 (c) CH3CCCH2OH (d) CH3CHO (e) CH3COOH

Specify which hybrid orbitals are used by carbon atoms in the following species: (a) CO, (b) CO2, (c) CN2.

What is the hybridization state of the central N atom in the azide ion, N3 2? (Arrangement of atoms: NNN.)

The allene molecule H2CCCH2 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.

Describe the hybridization of phosphorus in PF5.

How many sigma bonds and pi bonds are there in each of the following molecules? A H H A (a) (b) (c) CPC H A A H H3COCPCOCqCOH DCl G H H G H D ClOCOCl

How many pi bonds and sigma bonds are there in the tetracyanoethylene molecule? CPC DCqN G CqN NqCG NqC D

Give the formula of a cation comprised of iodine and fluorine in which the iodine atom is sp3 d- hybridized.

Give the formula of an anion comprised of iodine and fluorine in which the iodine atom is sp3 d2 - hybridized.

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

Sketch the shapes of the following molecular orbitals: 1s, w 1s, 2p, and w 2p. How do their energies compare?

Compare the Lewis theory, valence bond theory, and molecular orbital theory of chemical bonding.

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

Explain in molecular orbital terms the changes in HH internuclear distance that occur as the molecular H2 is ionized first to H2 1 and then to H2 21

The formation of H2 from two H atoms is an energetically favorable process. Yet statistically there is less than a 100 percent chance that any two 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 H atoms?

Draw a molecular orbital energy level diagram for each of the following species: He2, HHe, He2 1. Compare their relative stabilities in terms of bond orders. (Treat HHe as a diatomic molecule with three electrons.)

Arrange the following species in order of increasing stability: Li2, Li2 1, Li2 2. Justify your choice with a molecular orbital energy level diagram

Use molecular orbital theory to explain why the Be2 molecule does not exist.

Which of these species has a longer bond, B2 or B2 1? Explain in terms of molecular orbital theory.

Acetylene (C2H2) has a tendency to lose two protons (H1) and form the carbide ion (C2 22), which is present in a number of ionic compounds, such as CaC2 and MgC2. Describe the bonding scheme in the C2 22 ion in terms of molecular orbital theory. Compare the bond order in C2 22 with that in C2.

Compare the Lewis and molecular orbital treatments of the oxygen molecule.

Explain why the bond order of N2 is greater than that of N2 1, but the bond order of O2 is less than that of O2 1.

Compare the relative stability of the following species and indicate their magnetic properties (that is, diamagnetic or paramagnetic): O2, O2 1, O2 2 (superoxide ion), O2 22 (peroxide ion).

Use molecular orbital theory to compare the relative stabilities of F2 and F2 1.

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.

In 2009 the ion N2 32 was isolated. Use a molecular orbital diagram to compare its properties (bond order and magnetism) with the isoelectronic ion O2 2.

The following potential energy curve represents the formation of F2 from two F atoms. Describe the state of bonding at the marked regions. Potential energy r 0 + 3 4 5 2 1

How does a delocalized molecular orbital differ from a molecular orbital such as that found in H2 or C2H4? What do you think are the minimum conditions (for example, number of atoms and types of orbitals) for forming a delocalized molecular orbital?

In Chapter 9 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?

Both ethylene (C2H4) and benzene (C6H6) contain the CC bond. The reactivity of ethylene is greater than that of benzene. For example, ethylene readily reacts with molecular bromine, whereas benzene is normally quite inert toward molecular bromine and many other compounds. Explain this difference in reactivity

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.)

Nitryl fluoride (FNO2) is very reactive chemically. The fluorine and oxygen atoms are bonded to the nitrogen atom. (a) Write a Lewis structure for FNO2. (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?

Describe the bonding in the nitrate ion NO3 2 in terms of delocalized molecular orbitals.

What is the state of hybridization of the central O atom in O3? Describe the bonding in O3 in terms of delocalized molecular orbitals.

Which of the following species is not likely to have a tetrahedral shape? (a) SiBr4, (b) NF4 1, (c) SF4, (d) BeCl4 22, (e) BF4 2, (f) AlCl4 2

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

Sketch the bond moments and resultant dipole moments for the following molecules: H2O, PCl3, XeF4, PCl5, SF6.

Although both carbon and silicon are in Group 4A, very few SiSi 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 8.5. What effect would the larger size have on pi bond formation?)

Acetaminophen is the active ingredient in Tylenol. (a) Write the molecular formula of the compound. (b) What is the hybridization state of each C, N, and O atom? (c) Describe the geometry about each C, N, and O atom.

Caffeine is a stimulant drug present in coffee. (a) Write the molecular formula of the compound. (b) What is the hybridization state of each C, N, and O atom? (c) Describe the geometry about each C, N, and O atom.

7 Predict the geometry of sulfur dichloride (SCl2) and the hybridization of the sulfur atom.

Antimony pentafluoride, SbF5, reacts with XeF4 and XeF6 to form ionic compounds, XeF3 1SbF6 2 and XeF5 1SbF6 2. Describe the geometries of the cations and anion in these two compounds.

Draw Lewis structures and give the other information requested for the following molecules: (a) BF3. Shape: planar or nonplanar? (b) ClO3 2. Shape: planar or nonplanar? (c) H2O. Show the direction of the resultant dipole moment. (d) OF2. Polar or nonpolar molecule? (e) NO2. Estimate the ONO bond angle.

Draw Lewis structures and give the other information requested for the following molecules: (a) BF3. Shape: planar or nonplanar? (b) ClO3 2. Shape: planar or nonplanar? (c) H2O. Show the direction of the resultant dipole moment. (d) OF2. Polar or nonpolar molecule? (e) NO2. Estimate the ONO bond angle.

Briefly compare the VSEPR and hybridization approaches to the study of molecular geometry.

Describe the hybridization state of arsenic in arsenic pentafluoride (AsF5).

Draw Lewis structures and give the other information requested for the following: (a) SO3. Polar or nonpolar molecule? (b) PF3. Polar or nonpolar molecule? (c) F3SiH. Show the direction of the resultant dipole moment. (d) SiH3 2. Planar or pyramidal shape? (e) Br2CH2. Polar or nonpolar molecule?

Which of the following molecules and ions are linear? ICl2 2, IF2 1, OF2, SnI2, CdBr2

Draw the Lewis structure for the BeCl4 22 ion. Predict its geometry and describe the hybridization state of the Be atom.

The N2F2 molecule can exist in either of the following two forms: G D F F D DF F NPN NPN (a) What is the hybridization of N in the molecule? (b) Which structure has a dipole moment?

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 compound 1,2-dichloroethane (C2H4Cl2) is nonpolar, while cis-dichloroethylene (C2H2Cl2) has a dipole moment: Cl A A H Cl A A H 1,2-dichloroethane cis-dichloroethylene CPC ClG H D DCl G H HOCOCOH The reason for the difference is that groups connected 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-dichloroethane but not in cis-dichloroethylene

Does the following molecule have a dipole moment? CPCPC ClG H D D H G Cl (Hint: See the answer to Problem 10.39.)

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

The bond angle of SO2 is very close to 1208, even though there is a lone pair on S. Explain

39-azido-39-deoxythymidine, shown here, commonly known as AZT, is one of the drugs used to treat acquired immune deficiency syndrome (AIDS). What are the hybridization states of the C and N atoms in this molecule? A C A H O O B A A A C A H HOOCH2 H A C A N B N B N H A C A H NECHC A B CHNEC OK HH OCH3 HH

The following molecules (AX4Y2) all have octahedral geometry. Group the molecules that are equivalent to each other. X X Y Y A X X Y X X Y A X X X X Y X A X Y X X Y X A Y X (a) (b) (c) (d)

The compounds carbon tetrachloride (CCl4) and silicon tetrachloride (SiCl4) are similar in geometry and hybridization. However, CCl4 does not react with water but SiCl4 does. Explain the difference in their chemical reactivities. (Hint: The first step of the reaction is believed to be the addition of a water molecule to the Si atom in SiCl4.)

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

What are the hybridization states of the C and N atoms in this molecule? A NH2 A H NKCHC A B CHNEC OK HH EH

Use molecular orbital theory to explain the difference between the bond enthalpies of F2 and F2 2 (see Problem 9.110).

Referring to the Chemistry in Action essay on p. 426, answer the following questions: (a) If you wanted to cook a roast (beef or lamb), would you use a microwave oven or a conventional oven? (b) Radar is a means of locating an object by measuring the time for the echo of a microwave from the object to return to the source and the direction from which it returns. Would radar work if oxygen, nitrogen, and carbon dioxide were polar molecules? (c) In early tests of radar at the English Channel during World War II, the results were inconclusive even though there was no equipment malfunction. Why? (Hint: The weather is often foggy in the region.)

Which of the following molecules are polar? (a) (b) (c)

Which of the following molecules are polar? (a) (b) (c)

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 PP bond. Explain why P4 is more stable than P2.

Referring to Table 9.4, explain why the bond enthalpy for Cl2 is greater than that for F2. (Hint: The bond lengths of F2 and Cl2 are 142 pm and 199 pm, respectively.)

Use molecular orbital theory to explain the bonding in the azide ion (N3 2). (Arrangement of atoms is NNN.)

The ionic character of the bond in a diatomic molecule can be estimated by the formula ed 3 100% where is the experimentally measured dipole moment (in C m), e the electronic charge, and d the bond length in meters. (The quantity ed is the hypothetical dipole moment for the case in which the transfer of an electron from the less electronegative to the more electronegative atom is complete.) Given that the dipole moment and bond length of HF are 1.92 D and 91.7 pm, respectively, calculate the percent ionic character of the molecule.

Draw three Lewis structures for compounds with the formula C2H2F2. Indicate which of the compound(s) are polar.

Greenhouse gases absorb (and trap) outgoing infrared radiation (heat) from Earth and contribute to global warming. The 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 OPCPO OPCPO OPCPO g m n n nm h h where the arrows indicate the movement of the atoms. (During a complete cycle 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 to behave as a greenhouse gas? Which of the following molecules can act as a greenhouse gas: N2, O2, CO, NO2, and N2O?

Aluminum trichloride (AlCl3) is an electron- deficient molecule. It has a tendency to form a dimer (a molecule made of two AlCl3 units): AlCl3 1 AlCl3 S Al2Cl6 (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?

The molecules cis-dichloroethylene and transdichloroethylene shown on p. 425 can be interconverted by heating or irradiation. (a) Starting with cisdichloroethylene, show that rotating the CC bond by 180 will break only the pi bond but will leave the sigma bond intact. Explain the formation of trans-dichloroethylene from this process. (Treat the rotation as two stepwise 90 rotations.) (b) Account for the difference in the bond enthalpies for the pi bond (about 270 kJ/mol) and the sigma bond (about 350 kJ/mol). (c) Calculate the longest wavelength of light needed to bring about this conversion.

Progesterone is a hormone responsible for female sex characteristics. In the usual shorthand structure, each point where lines meet represent 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. O CH3 C K A A CH3A A CH3 PO

For each pair listed here, state which one has a higher first ionization energy and explain your choice: (a) H or H2, (b) N or N2, (c) O or O2, (d) F or F2.

The molecule benzyne (C6H4) is a very reactive species. It resembles benzene in that it has a sixmembered ring of carbon atoms. Draw a Lewis structure of the molecule and account for the molecules high reactivity

Assume that the third-period element phosphorus forms 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 (diamagnetic or paramagnetic)?

Consider a 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 N2* with N2, where the asterisk denotes the excited molecule. (c) Is N2* diamagnetic or paramagnetic? (d) When N2* 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.

As mentioned in the chapter, the Lewis structure for O2 is OQ O O O PQ Use the molecular orbital theory to show that the structure actually corresponds to an excited state of the oxygen molecule. 10.115 Referring to Problem 9.137, describe the hybridization state of the N atoms and the overall shape of the ion

Describe the geometry and hybridization for the reactants and product in the following reaction ClF3 1 AsF5 [ClF1 2 ][AsF2 6 ]

Describe the geometry and hybridization for the reactants and product in the following reaction ClF3 1 AsF5 [ClF1 2 ][AsF2 6 ]

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

TCDD, or 2,3,7,8-tetrachlorodibenzo-p-dioxin, is a highly toxic compound EO Cl O Cl Cl ECl E E E E E E It gained considerable notoriety in 2004 when it was implicated in the murder plot 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?

Write the electron configuration of the cyanide ion (CN2). Name a stable molecule that is isoelectronic with the ion.

Carbon monoxide (CO) is a poisonous compound due to its ability to bind strongly to Fe21 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 Fe21 ion in hemoglobin?

The geometries discussed in this chapter all lend themselves to fairly straightforward elucidation of bond angles. The exception is the tetrahedron, because its bond angles are hard to visualize. Consider the CCl4 molecule, which has a tetrahedral geometry and is nonpolar. By equating the bond moment of a particular CCl bond to the resultant bond moments of the other three CCl bonds in opposite directions, show that the bond angles are all equal to 109.5

Carbon suboxide (C3O2) is a colorless pungentsmelling gas. Does it possess a dipole moment?

Which of the following ions possess a dipole moment? (a) ClF2 1, (b) ClF2 2, (c) IF4 1, (d) IF4 2.

Given that the order of molecular orbitals for NO is similar to that for O2, arrange the following species in increasing bond orders: NO22, NO2, NO, NO1, NO21.

Shown here are molecular models of SX4 for X 5 F, Cl, and Br. Comment on the trends in the bond angle between the axial SX bonds in these molecules. SF4 SCl4 SBr4

Based on what you have learned from this chapter and Chapter 9, name a diatomic molecule that has the strongest known chemical bond and one with the weakest known chemical bond

The stability of benzene is due to the fact that we can draw reasonable resonance structures for the molecule, which is equivalent to saying that there is electron delocalization. Resonance energy is a measure of how much more stable benzene is compared to the hypothetical molecule, which can be represented by just a single resonance structure. Shown on p. 464 are the enthalpies of hydrogenation (the addition of hydrogen) of cyclohexene (C6H10) to cyclohexane (C6H12) and benzene to cyclohexane.1 H2 DH8 5 2120 kJ/mol1 3H2 DH8 5 2208 kJ/mol(In these simplified structures, each point wherelines meet represents a C atom. There is a H atomattached ta sp2- hybridized C atom and there aretwo H atoms attached to a sp3-hybridized C atom.)Estimate the resonance energy of benzene fromthese data.

How many carbon atoms are contained in one square centimeter of graphene (see the Chemistry in Action essay on p. 454 for a description of graphene)? What would be the mass of a 1-cm2 section of graphene?