Solution: For each of the following pairs of elements, state

Problem 1QP Explain Lewis’s contribution to our understanding of the covalent bond.

Problem 2QP Explain the difference between a Lewis symbol and a Lewis structure.

Problem 3QP Use examples to illustrate each of the following terms: lone pair, Lewis structure, octet rule, bond length.

Problem 5QP Explain how the octet rule applies to hydrogen.

Explain the octet rule and why it applies mainly to second period elements.

Problem 100AP Electrostatic potential maps for three compounds A, B, and C are shown below. Using the data in the following table, determine which compound corresponds to which electrostatic potential map and fill in the missing data in the table. Compound Partial charges Distance between charges (pm) Dipole moment ±0.16 157 ±0.43 3.10 258 8.89

Problem 6QP Compare single, double, and triple bonds in a molecule, and give an example of each. For the same bonding atoms, how does the bond length change from single bond to double bond to triple bond?

For a given pair of bonded atoms, explain how bond length relates to bond strength.

Problem 8QP For each of the following pairs of elements, state whether the binary compound they form is likely to be ionic or covalent. Write the empirical formula and name of the compound: (a) 1 and Cl, (b) Mg and F.

Problem 9QP For each of the following pairs of elements, state whether the binary compound they form is likely to be ionic or covalent. Write the empirical formula and name of the compound: (a) B and F, (b) K and Br.

Problem 12QP List the following bonds in order of increasing ionic character: the lithium-to-fluorine bond in LiF, the potassium-to-oxygen bond in K2O, the nitrogen-to-nitrogen bond in N2, the sulfur-to-oxygen bond in SO2, the chlorine-to-fluorine bond in C1F3.

Problem 13QP Arrange the following bonds in order of increasing ionic character: carbon to hydrogen, fluorine to hydrogen, bromine to hydrogen, sodium to chlorine, potassium to fluorine, lithium to chlorine.

Problem 11QP What is a polar covalent bond? Name two compounds that contain one or more polar covalent bonds.

Problem 10QP Define electronegativity, and explain the difference between electronegativity and electron affinity. Describe in general how the electronegativities of the elements change according to their position in the periodic table.

Four different atoms are represented by colored spheres: and Their electronegativities are as follows: = 3.8, = 3.3, = 2.8, and = 1.3. If the atoms of these elements form the molecules how would you arrange these molecules in order of increasing covalent bond character?

Problem 15QP List the following bonds in order of increasing ionic character: cesium to fluorine, chlorine to chlorine, bromine to chlorine, silicon to carbon.

Problem 16QP Classify the following bonds as ionic, polar covalent, or nonpolar covalent, and explain: (a) the CC bond in H3CCH3, (b) the KI bond in KI, (c) the NB bond in H3NBCl3, (d) the CF bond in CF4.

Problem 17QP Classify the following bonds as ionic, polar covalent, or nonpolar covalent, and explain: (a) the SiSi bond in Cl3SiSiCl3, (b) the SiCl bond in Cl3SiSiCl3, (c) the CaF bond in CaF2, (d) the NH bond in NH3.

Problem 18QP The radical species ClO has a dipole moment of 1.24 D and the Cl–0 bond distance is 1.57 Å. Determine the magnitude of the partial charges in ClO.

Problem 20QP The measured dipole moment of bromine monofluoride, BrF, is 1.42 D and the Br?F bond distance is 1.76 Å. Determine the percent ionic character of the bond in BrF.

Given that the partial charges on Al and F in aluminum monofluoride are +0.019 and –0.019, respectively, calculate the dipole moment of AlF. (The distance between the partial charges, r, is 165 pm.)

Given that the BaO bond has 85.3 percent ionic character and the \(\mathrm{Ba}-\mathrm{O}\) bond length is 194 pm, determine the measured dipole moment of BaO.

Problem 22QP Draw Lewis structures for the following molecules and ions: (a) NC13, (b) OCS, (c) H2O2, (d) CH3COO-, (e) CN-,

Problem 23QP Draw Lewis structures for the following molecules and ions: (a) OF2, (b) N2F2, (c) Si2H6, (d) OH-, (e) CH2CICOO-,

Problem 25QP Draw Lewis structures for the following molecules: (a) CIF3 (b) H2Se, (c) NH2OH. (d) POCl3 (P is bonded to 0 and Cl atoms), (e) CH3?H2Br, (f) NCI3, (g) CH3NH2.

Problem 24QP Draw Lewis structures for the following molecules: (a) ICl (b) PH3, (c) P4 (each P is bonded to three other P atoms), (d) H,S. (e) N2H4. (f) HClO3, (g) COBr2 (C isbonded to O and Br atoms).

Do formal charges represent an actual separation of charges?

Problem 28QP Draw Lewis structures for the following ions: Show formal charges.

Problem 29QP Draw Lewis structures for the following ions: Show formal charges.

Problem 26QP Explain the concept of formal charge.

Problem 31QP The skeletal structure of acetic acid shown here is correct, but some of the bonds are wrong, (a) Identify the incorrect bonds and explain what is wrong with them, (b) Write the correct Lewis structure for acetic acid.

Problem 30QP The following Lewis structures are incorrect. Explain what is wrong with each one, and give a correct Lewis structure for the molecule. (Relative positions of atoms are shown correctly.)

What are resonance structures? Is it possible to isolate one resonance structure of a compound for analysis? Explain.

Problem 33QP What are the rules for writing resonance structures?

Problem 34QP Draw three resonance structures for the chlorate ion . Show formal charges.

Problem 37QP Draw three resonance structures for hydrazoic acid (HN3). The atomic arrangement is HNNN. Show formal charges.

Draw two resonance structures for diazomethane \(\left(\mathrm{CH}_{2} \mathrm{~N}_{2}\right)). Show formal charges. The skeletal structure of the molecule is

Draw all of the resonance structures for the following species and show formal charges: (a) \(\mathrm{HCO}_2^{-}\), (b) \(\mathrm{CH}_2 \mathrm{NO}_2^{-}\). The relative positions of the atoms are as follows:

Problem 38QP Draw three resonance structures for the molecule N2O in which the atoms are arranged in the order NNO. Indicate formal charges.

Problem 39QP Draw three reasonable resonance structures for the OCN? ion. Show formal charges.

Problem 40QP Indicate which of the following are resonance structures of . For the others, explain why they are not resonance structures of . (a) . ________________ (b) . ________________ (c) . ________________ (d) . ________________ (e) .

Problem 41QP Indicate which of the following are resonance structures of (select all that apply). (a) ________________ (b) ________________ (c) ________________ (d) ________________ (e)

Draw one additional resonance structure of the adenine molecule shown here, which is part of the DNA structure.

Problem 44QP Why does the octet rule not hold for many compounds containing elements in the third period of the periodic table and beyond?

Problem 46QP Because fluorine has seven valence electrons (2s22p5), seven covalent bonds in principle could form around the atom. Such a compound might be FH7 or FCI7. These compounds have never been prepared. Why?

Problem 45QP Give three examples of compounds that do not satisfy the octet rule. Write a Lewis structure for each.

Problem 47QP What is a coordinate covalent bond? How is it different from an ordinary covalent bond? How is it the same?

Problem 43QP Draw a resonance structure of the guanine molecule shown here, which is part of the DNA structure.

Problem 48QP The AlI3 molecule has an incomplete octet around Al. Draw three resonance structures of the molecule in which the octet rule is satisfied for both the Al and the I atoms. Show formal charges.

Problem 49QP In the vapor phase, beryllium chloride consists of discrete BeCl2 molecules. Is the octet rule satisfied for Be in this compound? If not, can you form an octet around Be by drawing another resonance structure? Is this structure plausible? Explain.

Until the early 1960s, the noble gases were not known to form any compounds. Since then, a few compounds of Kr, Xe, and Rn—and one compound of Ar—have been made in laboratories. Draw Lewis structures for the following molecules: \(\text { (a) } \mathrm{XeF}_{2} \text {, (b) } \mathrm{XeF}_{4} \text {, (c) } \mathrm{XeF}_{6} \text {, }\)\(\text { (d) } \mathrm{XeOF}_{4} \text {, (e) } \mathrm{XeO}_{2} \mathrm{~F}_{2}\). In each case Xe is the central atom.

Problem 51QP Draw a Lewis structure for the tetrachloraluminate ion, . This ion can be considered as a combination of Alcl3 and Cl?. What kind of bond joins AlCl3 and Cl? in ?

Problem 53QP Write a Lewis structure for SbCl5. Does this molecule obey the octet rule?

Problem 52QP Write Lewis structures for SeF4 and SeF6. Is the octet rule satisfied for Se?

Problem 54QP Draw Lewis structures for the radical species CIF2 and BrO2.

Draw Lewis structures for the radical species \(\mathrm{HO}_{2}\) and ClO.

Draw Lewis structures for \(\mathrm{BrF}_{3}\), \(\mathrm{ClF}_{5}\), and \(\mathrm{IF}_{7}\). Identify those in which the octet rule is not obeyed.

Problem 56QP Draw two resonance structures for the bromate ion , one that obeys the octet rule and one in which the formal charge on the central atom is zero.

Problem 60AP The amide group plays an important role in determining the structure of proteins: Draw another resonance structure for this group. Show formal charges.

Problem 57QP Draw two resonance structures for the sulfite ion , one that obeys the octet rule and one in which the formal charge on the central atom is zero.

Problem 59AP Draw three reasonable resonance structures for the azide ion , in which the atoms are arranged as NNN. Show formal charges.

Give an example of an ion or molecule containing Al that (a) obeys the octet rule, (b) has an expanded octet, and (c) has an incomplete octet.

Problem 62AP Draw four reasonable resonance structures for the PO3F2- ion.The central P atom is bonded to the three O atoms and to the F atom.show formal charges.

Problem 63AP Attempts to prepare the compounds CF2, LiO2, CsCl2, and PI5 as stable species under atmospheric conditions have failed. Suggest possible reasons for the failure.

A rule for drawing plausible Lewis structures is that the central atom is generally less electronegative than the surrounding atoms. Explain why this is so.

Problem 67AP Which of the following molecules has the shortest nitrogen-to- nitrogen bond: N2H4, N2O, N2, N2O4? Explain.

Problem 64AP Draw reasonable resonance structures for the following ions: (a) , (b) , (c) , (d) .

Most organic acids can be represented as \(\mathrm{RCOOH}\), where \(\mathrm{COOH}\) is the carboxyl group and R is the rest of the molecule. [For example, R is \(\mathrm{CH}_3\) in acetic acid ( \(\left.\mathrm{CH}_3 \mathrm{COOH}\right)\).] (a) Draw a Lewis structure for the carboxyl group. (b) Upon ionization, the carboxyl group is converted to the carboxylate group \(\left(\mathrm{COO}^{-}\right)\). Draw resonance structures for the carboxylate group.

Problem 69AP Which of the following species are isoelectronic: NH4, C6H6, CO, CH4, N2, B3N3H6?

Problem 65AP Are the following statements true or false? (a) Formal charges represent an actual separation of charges. (b) All second-period elements obey the octet rule in their compounds, (c) The resonance structures of a molecule car. be separated from one another in the laboratory.

What are resonance structures? Is it possible to isolate one resonance structure of a compound for analysis? Explain.

The following is a simplified (skeletal) structure of the amino acid tryptophan. Draw a complete Lewis structure of the molecule.

Problem 73AP The sulfur oxides SO2 and SO3 are significant pollutants in the air and contributors to the formation of acid rain. It is thought that these compounds can be converted into radical anions inside of cells. Draw plausible Lewis structures of the radical anions and .

Draw Lewis structures for the following organic molecules: (a) tetrafluoroethylene \(\left(\mathrm{C}_{2} \mathrm{F}_{4}\right)\), (b) propane \(\left(\mathrm{C}_{3} \mathrm{H}_{8}\right)\), (c) butadiene \(\left(\mathrm{CH}_{2} \mathrm{CHCHCH}_{2}\right)\), (d) propyne \(\left(\mathrm{CH}_{3} \mathrm{CCH}\right)\), (e) benzoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)\). (To draw \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\), replace an H atom in benzene with a COOH group.)

Problem 72AP The following species have been detected in interstellar space: (a) CH, (b) OH, (c) C2, (d) HNC, (e) HCO. Draw Lewis structures for these species.

The triiodide ion \(\left(\mathrm{I}_{3}^{-}\right)\) in which the I atoms are arranged in a straight line is stable, but the corresponding \(\mathrm{F}_{3}^{-}\) ion does not exist. Explain.

Draw Lewis structures for the following organic molecules: \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{F}, \mathrm{C}_{3} \mathrm{H}_{6}, \mathrm{C}_{4} \mathrm{H}_{8}\). In each there is one C=C bond, and the rest of the carbon atoms are joined by C-C bonds.

Problem 77AP Methyl isocyanate (CH3NCO) is used to make certain pesticides. In December 1984, water leaked into a tank containing this substance at a chemical plant, producing a toxic cloud that killed thousands of people in Bhopal, India. Draw Lewis structures for CH3NCO, showing formal charges.

The chlorine nitrate \(\left(\mathrm{ClONO}_{2}\right)\) molecule is believed to be involved in the destruction of ozone in the Antarctic stratosphere. Draw a plausible Lewis structure for this molecule

Problem 79AP Several resonance structures for the molecule CO2 are shown here. Which of these species is/are most important in describing the bonding in this molecule? Explain why the others are less important. (a) ________________ (b) ________________ (c) ________________ (d)

For each of the following organic molecules draw a Lewis structure in which the carbon atoms are bonded to each other by single bonds: \(\text { (a) } \mathrm{C}_{2} \mathrm{H}_{6} \text {, (b) } \mathrm{C}_{4} \mathrm{H}_{10} \text {, }\) \(\text { (c) } \mathrm{C}_{5} \mathrm{H}_{12}\). For parts (b) and (c) show only structures in which each C atom is bonded to no more than two other C atoms.

Problem 84AP Oxygen forms three types of ionic compounds in which the anions are oxide (O2-), peroxide , and superoxide . Draw Lewis structures of these ions.

Problem 83AP Write Lewis structures for the following four isoelectronic species: (a) CO, (b) NO-, (c) CN-, (d) N2. Show formal charges.

Problem 82AP Draw Lewis structures for the following organic molecules:(a)methanol (CH3OH); (b) ethanol (CH3CH2OH); (c) tetraethyl lead [Pb(CH2CH3)4], which is used in "leaded gasoline";(d)methylamine (CH3NH2), which is used in tanning;(e)mustard gas (ClCH2CH2SCH2CH2CI), a poisonous gas used in World War I; (f) urea [(NH2)2CO], a fertilizer; and (g) glycine (NH2CH2COOH), an amino acid.

Problem 85AP Is there a group of elements that always violates the octet rule? Explain.

Problem 81AP Draw Lewis structures for the following chlorofluorocarbons (CFCs), which are partly responsible for the depletion of ozone in the stratosphere: (a) CFC13, (b) CF2C12, (c) CHF2C1, (d) CF3CHF2.

The \(\mathrm{N}-\mathrm{O}\) bond distance in nitric oxide is \(115 \mathrm{pm}\), which is intermediate between a triple bond (106 pm) and a double bond (120 pm). (a) Draw two resonance structures for \(\mathrm{NO}\), and comment on their relative importance. (b) Is it possible to draw a resonance structure having a triple bond between the atoms?

Problem 86AP Write three resonance structures for (a) the cyanate ion (NCO-) and (b) the isocyanate ion (CNO-). In each case, rank the resonance structures in order of increasing importance.

Problem 90AP Draw a Lewis structure for nitrogen pentoxide (N2O5) in which each N is bonded to three O atoms.

Problem 88AP Within the comet Hale-Bopp, a number of sulfur- containing diatomic molecules have been detected including sulfur mononitride (SN) and sulfur monoxide (SO), (a) Determine the partial charges in SN given the dipole moment (1.81 D) and S?N bond distance (149 pm), (b) If the partial charges on S and 0 in sulfur monoxide are +0.022 and ?0.022, respectively, calculate the dipole moment of SO. (The distance between the partial charges, r, is 1.48 Å.)

In the gas phase, aluminum chloride exists as a dimer (a unit of two) with the formula \(\mathrm{Al_2 Cl_6}\). Its skeletal structure is given by Complete the Lewis structure and identify the coordinate covalent bonds in the molecules. Would you expect this molecule to be polar? Explain.

Determine the percent ionic character of RbF and of RbI. The dipole moments of RbF and RbI are 8.55 D and 11.48 D, respectively. [Use information from Figure 4.13 (page 127) to calculate the bond distances in each ionic compound.] Comment on the difference between your two answers.

Nitrogen dioxide \(\left(\mathrm{NO}_2\right)\) is a stable compound. Explain why there is a tendency for two such molecules to combine to form dinitrogen tetroxide \(\left(\mathrm{N}_2 \mathrm{O}_4\right)\). Draw four resonance structures of \(\mathrm{N}_2 \mathrm{O}_4\), showing formal charges.

Problem 93AP Electrostatic potential maps for three compounds A. B, and C are shown below. Using the data in the following table, determine which compound corresponds to which electrostatic potential map and determine the dipole moment of each compound. Fill in the missing data in the table. Compound Partial charges Distance between charges (pm) Dipole moment ±0.19 213 ±0.051 214 ±0.68 315

Vinyl chloride \(\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Cl}\right)\) differs from ethylene \(\left(\mathrm{C}_{2} \mathrm{H}_{4}\right)\) in that one of the H atoms is replaced with a Cl atom. Vinyl chloride is used to prepare poly(vinyl chloride), which is an important polymer used in pipes. (a) Draw the Lewis structure of vinyl chloride. (b) The repeating unit in poly(vinyl chloride) is \(-\mathrm{CH}_{2}-\mathrm{CHCl}-\text {. }\) Draw a portion of the molecule showing three such repeating units.

Pyridine has a structure similar to that of benzene, but one of the carbon atoms (and the hydrogen bonded to it) are replaced by a nitrogen atom. Draw the two resonance structures of pyridine and using information from Table 6.1, estimate the length of the \(\mathrm{C}-\mathrm{N}\) bonds.

Problem 97AP In 1999 an unusual cation containing only nitrogen was prepared. Draw three resonance structures of the ion, showing formal charges.(Hint: The N atoms are joined in a linear fashion.)

Problem 99AP The American chemist Robert S. Mulliken suggested a different definition for the electronegativity (EN) of an element, given by where IE1 is the first ionization energy and EA is the electron affinity of the element. Calculate the electronegativities of O, F, and Cl using the preceding equation. Compare the electronegativities of these elements on the Mulliken and Pauling scales. (To convert to the Pauling scale, divide each EN value by 230 kJ/mol.)

Problem 96AP Among the common inhaled anesthetics are: Halothane (CF3CHClBr) Isoflurane (CF3CHCIOCHF2) Enflurane (CHFC1CF2OCHF2) Methoxyflurane (CHC12CF2OCH3) Draw Lewis structures of these molecules.

Problem 98AP In each of the following Lewis structures, Z and X represent different third-period main group elements. Draw the Lewis structure for the compound ZX3.