The Foundations of Chemistry

350 CHAPTER 8: Molecular Structure and Covalent Bonding Theories

Molecule Electronic Molecular Hybridization

or Ion Geometry Geometry of the Sulfur Atom

SO 2

SCl 2

SO 3

SO 32 

SF 4

SO 42 

SF 5 

SF 6

angles of about 109°. What can you infer from these facts

about the repulsive force exerted by an unpaired, unshared

electron as compared with that exerted by an unshared pair

of electrons?

*73.Two Lewis structures can be written for the square planar

molecule PtCl 2 Br 2 :

Show how a difference in dipole moments can distinguish

between these two possible structures.

*74.(a) Describe the hybridization of N in NO 2 and NO 2 
.

(b) Predict the bond angle in each case.

*75.The skeleton and a ball-and-stick model for the nitrous

acid molecule, HNO 2 , are shown here. Draw the Lewis

formula. What are the hybridizations at the middle O and

N atoms?

*76.Describe the change in hybridization that occurs at the

central atom of the reactant at the left in each of the fol-

lowing reactions.

(a) PF 5 F
nPF 6 


(b) 2COO 2 n2CO 2

(c) AlI 3 I
nAlI 4 


(d) What change in hybridization occurs in the following

reaction?

*77.Consider the following proposed Lewis formulas for ozone

(O 3 ):

(a) Which of these correspond to a polar molecule?

(b) Which of these predict covalent bonds of equal lengths

and strengths? (c) Which of these predict a diamagnetic

molecule? (d) The properties listed in parts (a), (b), and (c)

are those observed for ozone. Which structure correctly

predicts all three? (e) Which of these contain a consider-

able amount of “strain”? Explain.

(iii) O O O

OO

O

(i) O O O O O O (ii)

NH 3 BF 3 H 3 N BF 3

H

N

104 

116 

1.45Å

0.98Å

O

O

Pt

Cl

Cl

Br

Br

Pt

Cl

Cl

Br

Br

and

*78.What hybridizations are predicted for the central atoms in

molecules having the formulas AB 2 U 2 and AB 3 U? What

are the predicted bond angles for these molecules? The

observed bond angles for representative substances are

H 2 O 104.5° NH 3 106.7°

H 2 S 92.2° PH 3 93.7°

H 2 Se 91.0° AsH 3 91.8°

He 2 Te 89.5° SbH 3 91.3°

What would be the predicted bond angle if no hybridiza-

tion occurred? What conclusion can you draw concerning

the importance of hybridization for molecules of com-

pounds involving elements with higher atomic numbers?

CONCEPTUAL EXERCISES

*79.Draw and explain the difference in the three-dimensional

shapes of CH 3 CH 2 CH 3 and CH 3 COCH 3.

*80.Complete the following table.

*81.Compare the shapes of the following pairs of molecules:

(a) H 2 CO and CH 4 ; (b) PbCl 4 and PbO 2 ; (c) CH 4 and

PbCl 4.

*82.(a) Write two Lewis formulas for CO 32 
. Do the two for-

mulas represent resonance forms? (b) Do the same for

HSO 4 
.

*83.What advantages does the VSEPR model of chemical

bonding have compared with Lewis formulas?

*84.What evidence could you present to show that two carbon

atoms joined by a single sigma bond are able to rotate about

an axis that coincides with the bond, but two carbon atoms

bonded by a double bond cannot rotate about an axis along

the double bond?