Chemistry Assignment #3 (Ch. 8,9)
8.24 Explain the following trends in lattice energy:
(a) MgO > MgCI2; (b) NaCI > RbBr > CsBr;
(c) BaO > KF.
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.
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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)
(c) 8 H2S(g) ~ 8 H2(g) + S8(s)
(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).
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9.26 Give approximate values for the indicated bond angles
in the following molecules:
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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?
(c) What type of hybridization exists in SiH4? (d) In one
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?
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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?
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