1.1 Write Lewis Structures for each of the following:
(c) CH3F
(a) HF
(e) H2SO3
-
(d) HNO2
(b) F2
(f) BH4
(g) H3PO4
( i) HCN
(h) H2CO3
H
H
F
F
F
H
C
O
F
N
O
H
H
O
H
O
S
O
H
O
H
H
H
H
B
O
P
O
H
O
H
H
O
H
O
C
O
H
H
C
N
1.2 Write a Lewis structure for each of the following negative ions, and assign the formal negative
charge to the correct atom.
(a) NO2-
(c) CN-
(b) NH2-
Answer:
(a)
O
O
N
(b)
H
N
H
(c)
C
N
(d)
O
O
(e)
S
O
O
H
(d) HSO4-
(e) HCO3-
(f) HC2-
O
C
H
O
O
(f)
C
H
C
1.3 Assign the proper formal charge to the colored atom in each of the following structures:
H
(a)
H
H
H
C
C
H
H
O
+1
H
H
(b)
+1
O
(c)
H
C
O
-1
O
H
C
H
(d)
H
(e)
(f)
H
-1
H
H
C
N
H
H
H
O
H
H
C
H
H
H
+1
+1
1.4 Write two resonance structures for the formula ion HCO2-. (b) Explain what these structures predict
for the carbon-oxygen bond lengths of the formate ion and (c) for the electrical charge on the oxygen
atoms.
H
H
C
C
O
O-
-O
O
The structure predicts that the carbon-oxygen bond lengths will be between the carbon-oxygen single
bond and carbon-oxygen double bond. And each oxygen atom should bear -1/2 negative charge.
1.5
(a) Consider a carbon atom in its ground state. Would such an atom offer a satisfactory model for the
carbon of methane? If not, why not?
(b) What about a carbon atom in the exited state:
C
1s
2s
2px
2py 2pz
Excited state of a carbon atom
Would such a atom offer a satisfactory model for the carbon of methane? If not, why not?
Answer: (a) The ground state of a carbon atom is:
C
1s
2s
2px
2py
2pz
It has only two unpaired electrons. So it only can form two covalent bonds with hydrogens.
But in methane, there are four carbon-hydrogen bonds.
H
H
C
H
H
If it is combined with hydrogen atoms, the bond angle is 900. Because the angle between
2Px and 2Py is 900. So a carbon atom in its ground state can not offer a satisfactory model
for the carbon of methane.
(b) A carbon atom in the exited state can offer a satisfactory model for the carbon of
methane. It has four unpaired electrons. So it can form four covalent bonds with
hydrogens.
1.6 which of the following alkenes can exit as cis-trans isomers? Write their structures.
a
b
c
d
Cl
ANSWER
only c and d exit as cis-trans isomers
to c
H3C
CH3
C
C
C
H
Cl
C
C
H3C
H
H
to d
CH3
H
H
Cl
H3CH2C
C
C
H3CH2C
H
H
C
H
1.7 Part of reasoning that led van't Hoff and Le Bel to propose a tetrahedral shape for molecules of
methane was based on the number of isomers possible for substituted methanes. For example, only one
compound with the formula CH2Cl2 has ever been observed (i.e., there is no isomeric form). Consider
both a square planar structure and a tetrahedral structure for CH2Cl2 and explain how this observation
supports a tetrahedral structure.
If CH2Cl2' structure is square planar shape, it must has two isomers as follow:
Cl
H
Cl
H
Cl
H
H
Cl
If CH2CL2' structure is tetrahedral structure, as we know it just has one structure. Only one compound
with the formula CH2Cl2 has been observed, so that we propose CH2Cl2'structure is a tetrahedal shape.
H
H
Cl
Cl
1.8 Use VSEPR theory and predict the geometry of each of the following molecules and ions:
(a) BH4-
(c) NH4+
(e) BH3
(g) SiF4
(b) BeF2
(d) H2S
(f) CF4
(h) :CCL3-
(a) tetrahedral shape
(b) linear geometry
(c) tetrahedral shape
(d) angular shape
(e) trigonal planar shape
(f) tetrahedral shape
(g) tetrahedral shape
(h) trigonal pyramid
1.9 Predict the bond angles of (a) F2C=CF2,(b) CH3C≡CCH3,(c) HC≡N.
Answer:
(a)
F
F
120 o
120 o
F
F
(b)
H
H
109.28 o
H
180 o
H
H
H
(c)
180 o
H
N
1.10 There are actually three constitutional isomers with the molecular formula C3H8O. We have seen
two of them in propyl alcohol and isopropyl alcohol. Write a dash formula for the third isomer.
Answer:
H
H
C
O
H
H
H
C
C
H
H
H
1.11 Outline the carbon skeleton of the following condensed structural formulas and then write
each as a bond-line formula.
H2
C
H3 C
(a)
CH
CH3
CH3
H2
C
(b)
H3C
OH
CH
C
H2
CH3
(c)
H
C
H3C
CH3
C
H2
CH3
(d)
H2
C
H3C
(e)
CH3
C
H2
C
H2
H2
C
H2
C
H3C
CH
CH3
OH
OH
(f)
H2
C
H2C
C
CH3
H2C
CH3
O
O
H2
C
(g) H C
3
C
H2
C
H2
Cl
CH3
CH
(h)
CH3
Cl
CH
H3C
C
H2
CH3
1.12 Which molecules in Problem 1.11 form sets of constitutional isomers?
(a) ( CH3)2CHCH2CH3
(b) (CH3)2CHCH2CH2OH
(c) (CH3)2C=CHCH2CH3
(d) CH3CH2CH2CH2CH3
(e) CH3CH2CH(OH)CH2CH3
(f) CH2=C(CH2CH3)2
(g) CH3COCH2CH2CH2CH3
Answer:
(h) CH3CHClCH2CH(CH3)2
sets of constituational isomers:
(a) and (b), (b) and (e), (c) and (f)
1.13 Write dash formulas for each of the following bond-line formulas:
OH
Cl
O
Answer:
O
H Cl
H
C
H
H
H
H
C
C
H
C
H
H
H
H
C
H
H
H
C
H
H
C
C
H
C
C
H
C
H
H
C
H
O
C
C
C
C
C
H
H
H
H
H
H
H
H
C
C
H
H
H H
C
H
H
H
H
C
C
C
H
H
H
H
1.14 Write three-dimensional (wedge-dashed wedge-line) representations for each of the following:
(a) CH3Cl, (b) CH2Cl2,
(c) CH2BrCl, (d) CH3CH2Cl.
Answer:
H
(a)
H
(c)
(b)
C
H
Cl
Cl
H
H
H
H
C
H
Br
Cl
C
(d)
C
Cl
Cl
H
H
H
H
1.15 Which of the following ions posses the electron configuration of a noble gas?
(a) Na+
(b) Cl-
(c) F+
(d) H-
(e) Ca2+
(f) S2-
(g) O2(h) Br+
Answer:
(a) Na+
(b) Cl-
(e) Ca2+ (g) O2(d) H(f) S2-
These ions have the electron configuration of a noble gas.
1.16 Write Lewis structures for each of the following:
(a) SOCl2
(b) POCl3
(c) PCl5
(d) HONO2(HNO3)
Answer:
Cl
Cl
(a)
Cl
O
(b) Cl
S
O
Cl
P
O
(c)
(d)
P
Cl
H
N
O
Cl
Cl
O
Cl
Cl
1.17 Give the formal charge<if one exits>on each atom of the following:
O
H3C
O
S
O
H3 C
S
CH3
O
S
O
O
1.18 Write a condensed structural formula for each compound given here.
(a)
OH
(b)
O
O
O
O
CH3
S
O
O
O
(c)
(d)
OH
Answer
(a) (CH3)2CHCH2OH
O
(b) (CH3)2CHCCH(CH3)2
HC
CH
(c) H2C
CH2
(d) (CH3)2 CHCH2CH2OH
1.19 What is the molecular formula for each of the compounds givenin Problem 1.18?
Answer:
(a)
C4H10O
(b) C7H14O
(c)
C4H6
(d) C5H12O
1.20 Consider each pair of structural formulas that follow and state whether the two formulas represent
the same compound, whether they present different compounds that are constitutional isomers of each
other or whether they represent different compounds that are not isomeric.
(a)
Br
and
Cl
(b)
CH3CH2CH2
and
Cl
Br
different compounds
not isomeric
ClCH2CH(CH3)2
different compound
constitutional isomers
CH2Cl
H
H
(c)
C
H
Cl
and
Cl
C
the same compound
Cl
H
Cl
(d)
H
H
H
and
F
C
C
H
H
C
H
HC
F
CH2FCH2CH2CH2 F
the same compound
H
(e)
CH3
H3C
C
And
(CH3)3C
the same compound
CH3
CH3
CH3
CH3
(f)
2HC
CHCH2CH3
H2C
(g)
CH3OCH2CH3
and
different compound
CH
and
H3C
constitutional isomer
CH2
C
O
CH3
different compound
not isomeric
(h)
CH3CH2CH2 CH3
and
CH3CH2
the same compound
CH2CH3
O
(i)
CH3OCH2CH3
C
and
CH2
(j)
CH2ClCHClCH3
(k)
CH3CH2CHClCH2 Cl
different compounds
not isomeric
CH2
CH3CHClCH2Cl
and
and
the same compound
CH3CHCH2Cl
different compounds
constitutional isomers
CH2Cl
O
O
(l)
not isomeric
C
H2 C
CH2
H
Cl
(m)
different compounds
and
CH3CCH3
the same compound
and
C
H
Cl
Br
H
CH3
H
Br
H
H
(n)
C
C
H
the same compound
H
and
H3C
C
H
CH3
H
H
H
H
F
H
(o)
same compounds
H
H
F
F
H
H
F
H
F
H
H
H
(p)
Constitutional isomers
H
H
F
F
F
H
1.21. Rewrite each of the following using bond-line formulas:
(a) CH3CH2CH2COCH3
O
(b) CH3CH(CH3)CH2CH2CH(CH3)CH2CH3
(c) (CH3)3CCH2CH2CH2OH
OH
(d) CH3CH2CH(CH3)CH2COOH
OH
O
(e) CH2=CHCH2CH2CH=CHCH3
(f)
O
O
C
HC
CH2
CH2
HC
C
H2
1.22 Write a dash formula for each of the following showing any unshared electron pairs:
O
N
(a)
H
(b)
N
(c) (CH3)2NCH2CH3 (d)
Answer:
H
H
(a)
H
H
H
H
C
C
C
C
N
H
(b)
H
C
H
C
C
C
H
H
C
H
C
N
H
H
H
H
H
H
H
H
(d)
C
(c)
C
C
C
H
H
H
O
H
H
H
H
H
N
H
H
H
H H
H
H
1.23 Write structural formulas of your choice for all of the constitutional isomers with the molecular
formula C4H8.
1)
2)
3)
4)
H 2C
C
H
C H2
CH3
H 3C
C
H
CH
CH3
H2C
5)
C
CH3
CH3
1.24 Write structural formulas for at least three constitutional isomers with the molecular CH3NO2. (In
answering this question you should assign a formal charge to any atom that bears one.)
Answer:
O
O
H3C N
O
H
O
N OH
H
H2N
OH
1.25 Cyanic acid (H—O—C≡N) and isocyanic acid (H—N＝C＝O) differ in the positions of
their electrons but their structures do not represent resonance structures. (a) Explain. (b) Loss of a
proton from cyanic acid yieds the same anion as that obtained by loss of a proton from isocyanic
acid. Explain.
Answer:
(a) : While the structures differ in the position of their electrons, they also differ in the
positions of their nuclei and thus they are not resonance structures.
(b) : The anion obtained from either acid is a resonance hybrid of the following structures.
O
C
N
O
C
N
1.26 Consider a chemical species (either a molecule or anion) in which a carbon atom forms three
single bonds to three hydrogen atoms, and in which the carbon atom possesses no other valence
electrons. (a) What formal charge would the carbon atom have? (b) What total charge would the
species have? (c) What shape would you expect this species to have? (d) What would you expect
the hybridization state of the carbon atom to be?
Answer: (a) A + charge.
(b) +1
(c) Trigonal plannar
(d) sp2
1.27 Consider a chemical species like the one in the previous problem in which a carbon atom
forms three single bonds to three hydrogen atoms, but in which the carbon atom possesses an
unshared electron pair.
(a) What formal charge would the carbon atom have?
(b) What total charge would the species have?
(c) What shape would you expect this species to have?
(d) What would you expect the hybridization state of the carbon atom to be?
Answer:
(a) The carbon atom will have a negative formal charge.
(b) The species will a negative charge.
(c) The species will have the identical shape, which is the trigonal pyramidal shape, as the NH3
molecule.
(d) The carbon atom must be the sp3 hybridization.
1.28 Consider a chemical species (either a molecule or an ion) in which a carbon atom forms three
single bonds to three hydrogen atoms, but in which the carbon atom possesses a single unpaired
electron. (a) What formal charge would the carbon atom have? (b) What total charge would the
species have? (c) Given that the shape of this species is trigonal planner, what would you expect
the hybridization state of the carbon atom to be?
Answer:
The formal charge of carbon: 4-4=0;
The formal charge of the three hydrogen atoms:
1-1=0;
Charge on the molecule: 0+0=0;
As the species is trigonal planner, and has an unpaired electron in carbon’s P orbital, that the
carbon is SP2 hybridized.
1.29 Ozone (O3) is found in the upper atmosphere where it absorbs highly energetic ultraviolet
(UV) radiation and thereby provides the surface of the Earth with a protective screen (cf. Section
10.11E). One possible resonance structure for ozone is the following:
O
O
O
(a) Assign any necessary formal charges to the atoms in this structure.
(b) Write another equivalent resonance structure for ozone.
(c) What do these resonance structures predict about the relative lengths of the two
oxygen-oxygen bonds of ozone?
(d) The structure above, and the one you have written, assumes an angular shape for the ozone
molecule. Is this shape consistent with VSEPR theory? Explain your answer.
Answer
(a)
formal charge=6-5=1
O
O
O
formal charge=6-6=0
formal charge=6-7=-1
charge on molecule=1+0+(-1)=0
(b)
O
O
O
O
O
O
(c) Because the two resonance structures are equivalent, they should make equal contribution to
hybrid and, therefore, the bonds should be the same length.
(d) Yes. The VSEPR method can also used to predict the shapes of a molecule of ozone. We
assume all of the electrons of a multiple bond act as though they were a single unit and, therefore,
are located in the region of space between the two atoms joined by a multiple bond. The center
oxygen atom of ozone is bonded to another two oxygen atoms by a single bond and a double bond.
So the structure has a bond angular because the nonbonding pairs are effectively “larger” than the
bonding pairs and, therefore the structure is not linear.
1.31 Write structural formulas of the type indicated:
(a) Bond-line formulas for seven constitutional isomers with the formula C4H10O
Solution:
OH
OH
HO
HO
,
,
,
O
O
O
,
,
(b) Condensed structural formulas for two constitutional isomers with the formula C2H7N
Solution: CH3CH2NH2,CH3NHCH3
(c) Condensed structural formulas for form constitutional isomers with the formula C3H9N
CH3CHCH3
CH3CHNH2
Solution: CH3CH2CH2NH2,
CH3
,CH3NHCH2CH3,
NH2
(d) Bond-line formulas for three constitutional isomers with the formula C5H12
,
Solution:
,
1.32 What is the relationship between the members of the following pairs? That is, are they
constitutional isomers, the same, or something else (specify).
(a)
NH2
NH3
constitutional isomers
(b)
CH3CH2CH2CH(CH3 )2
the same
(c)
NH2
NH2
resonance structures
(d)
NH2
NH3
constitutional isomers
(e)
O
O
C
H3C
C
NH2
H3C
NH2
resonance structures
(f)
Cl
Cl
Cl
Cl
the same
1.33 In chapter 15 we shall learn how the nitronium ion, NO2+, forms when concentrated nitric
and sulfuric acids are mixed. (a) Write a Lewis structure for the nitronium ion. (b) What geometry
does VSEPR theory predict for the NO2+ ion? (c) Give a species that has the same number of
electrons as NO2+.
ANWSER:
(a) The Lewis structure
O N O
(b)
The geometry
O
N
O
(c)
Such as
CO2
1.34 Given the following sets of atoms, write bond line formulas for all of the possible
constitutionally isomeric compounds or ions that could be made from them. Show all unshared
electron pairs and all formal charges, if any.
Set
C atoms
H atoms
Other
A
3
6
2 Br atoms
B
3
9
1 N atoms & 1Oatom(not on same C)
C
3
4
1 O atom
D
2
7
1 N atom & 1proton
E
3
7
1 extra electron
Answer:
A
Br
Br
Br
Br
Br
Br
Br
Br
B
NH2
OH
H2N
OH
OH
NH2
H
N
O
N
OH
H
N
OH
NH2
OH
N
CH3
O
C
H
HO
O
C
O
O
H3C
D
N
H3N
H
H
E
CH
H3C
CH2
CH3
H2C
CH3
O