Chemistry Assignment #3 (Ch. 8,9)

Chemistry Assignment #3 (Ch. 8,9)

8.24 Explain the following trends in lattice energy:

(a) MgO > MgCI2; (b) NaCI > RbBr > CsBr;

8.64 (a) Describe the molecule chlorine dioxide, CI02, using

three possible resonance structures. (b) Do any of these

resonance structures satisfy the octet rule for every atom

in the molecule? Why or why not? (c) Using formal

charges, select the resonance structure(s) that is (are)

most important.

8.68 Use bond enthalpies (Table 8.4) to estimate the enthalpy

change for each of the following reactions:

(a) 3 H2C=CH2(g) ~ C6H12(g) (the six carbon atoms

from a six-membered ring with two hydrogen atoms

on each carbon atom)

(b) SiClH3(g) + 3 CI2(g) ~ SiCI4(g) + 3 HCI(g)

(See Figure 7.28. Strictly speaking, the average bond enthalpy

values apply to species in the gas phase. The heat

of formation of S8(g) is 102.3 kJ/mo!. Apply the needed

correction in order to estimate the enthalpy change for

the reaction as shown.)

8.99 The compound chloral hydrate, known in detective stories

as knockout drops, is composed of 14.52% C, 1.83%

H, 64.30% CI, and 19.35% 0 by mass and has a molar

mass of 165.4 g/mol. (a) What is the empirical formula

of this substance? (b) What is the molecular formula of

this substance? (c) Draw the Lewis structure of the molecule,

assuming that the CI atoms bond to a single C

atom and that there is a C-C bond and two C-O

bonds in the compound.

8.105 Consider benzene (C6H6) in the gas phase. (a) Write the

reaction for breaking all the bonds in C6H6(g), and use

data in Appendix C to determine the enthalpy change

for this reaction. (b) Write a reaction that corresponds to

breaking all the carbon-carbon bonds in C6H6(g). (c) By

combining your answers to parts (a) and (b) and using

the average bond enthalpy for C- H from Table 8.4, calculate

the average bond enthalpy for the carbon-carbon

bonds in C6H6(g). (d) Comment on your answer from

part (c) as compared to the values for C-C single

bonds and C=C double bonds in Table 8.4 (p.3).

9.26 Give approximate values for the indicated bond angles

in the following molecules:

9.38 Dichlorobenzene, C6H4Cl2, exists in three forms (isomers),

called ortho, meta, and para:

JvCI ortho meta para

Which of these would have a nonzero dipole moment?

Explain.

9.42 (a) Draw a Lewis structure for silane (SiH4), and predict

its molecular geometry. (b) Is it necessary to promote an

electron before forming hybrid orbitals for the Si atom?

diagram, sketch two of the two-electron bonds formed

between a hybrid orbital on Si and an H Is orbital. How

would the other Si- H bonds be oriented relative to

your sketch?

9.72 (a) The nitric oxide molecule, NO, readily loses one electron

to form the NO+ ion. Why is this consistent with

the electronic structure of NO? (b) Predict the order of

the N -0 bond strengths in NO, NO+, and NO-, and

describe the magnetic properties of each. (c) With what

neutral homonucIear diatomic molecules are the NO+

and NO- ions isoelectronic (same number of electrons)?

9.88 Butadiene, C4H6, is a planar molecule that has the following

carbon-carbon bond lengths:

(a) Predict the bond angles around each of the carbon

atoms, and sketch the molecule. (b) Compare the bond

lengths to the average bond lengths listed in Table 8.5.

Can you explain any differences?