C HAPTER 1 HW S OLUTIONS : S TRUCTURE
FORMAL CHARGE
1. Indicate the formal charge on any atom that has a non-zero formal charge.
a.
c.
b.
H
H
O
C
C
6-7 = -1
H
H
H
H
H
C
N
H
H
H
H
H
H
H
C
C
H
H
C
C
H
g.
f.
e.
d.
H 5-4 = +1
O
H
H
C
H
H
4-3 = +1
h.
C
H
N
H
H
C
H
H
4-5 = -1
i.
j.
H
C
C
C
H
O
C
H
H
6-5 = +1
C
H
C
P
H
H
N
H
O
O
N
6-6 = 0
5-5 = 0
N
N
(see 1e and 1g)
H
LEWIS STRUCTURES
2. Draw the Lewis structure for each formula, including lone pairs and formal charge. If a condensed formula is
given, the atoms are in the implied order. The general connectivity of atoms is shown in problem g.
20 valence e–
a. C2H5Cl
H
H
H
C
C
H
10 valence e–
b. CO
C
Cl
H
14 valence e–
e. CH3CH2−
H
H
O
H
H
H
H
C
O
H
12 valence e–
f. HNNH
H
C
C
H
H
H
N
N
H
34 valence e–
H
H
C
O
14 valence e–
H
C
g. C4H5O2−
O
O
H
d. CH3OH2+
18 valence e–
c. HCO2H
H
C
C
O
C
H
H
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RESONANCE STRUCTURES
3. In each set, decide which is the major resonance contributor, and explain your answer. Then draw the resonance
hybrid. If charge is unequally distributed in the resonance hybrid, make that obvious with the size of the partial
charges.
a.
H
C
C
C
H
H
H
H
H
C
C
C
H
H
H
δ−
H
H
δ−
C
C
C
H
H
H
H
These contribute equally to the resonance hybrid since in both all atoms have octets (except H which has
a duet) and put the negative charge on the same atom (carbon).
b.
CH3 C
N
H
H
H
CH3 C
N
H
H
δ+ δ+
H
CH3 C
N
H
H
H
The structure on the right is the major contributor, as each atom has an octet. In the resonance structure
on the left, one carbon atom doesn’t have an octet so contributes less to the hybrid.
4. In each set, rank the resonance structures in order from most to least important to the overall resonance hybrid.
Explain your answer.
O
O
a.
CH3 C
O
H
O
CH3 C
O
H
CH3 C
O
H
MAJOR (#1)
#3
#2
The first structure is neutral and all atoms have an octet (besides of course H which has a duet), so it
contributes the most to the hybrid. The other resonance structures are charged, so contribute less. The
one marked #3 is the least important because the positively charged carbon does not have an octet.
H
H
b.
H
C
H
C
H
C
C
O
C
H
H
H
H
C
H
C
H
H
H
C
C
H
H
O
C
H
C
H
C
C
O
C
H
H
H
C
H
#2
#3
MAJOR
The structure marked #3 is least important because a carbon does not have an octet. All atoms in the others
structures have octets, so contribute more to the hybrid. The structure marked MAJOR has the negative
charge on oxygen, which is highly electronegative and stabilizes the charge better than the negative charge
on the carbon in #2.
H
c.
H
O
CH3 C
N
H
H
H
O
CH3 C
N
H
H
O
CH3 C
N
H
H
#2
#3
MAJOR
The structure marked MAJOR has the positive charge on nitrogen, which is less electronegative than
oxygen (where the charge is on #2). The positive charge is destabilized by the oxygen in structure #2.
Structure #3 has a carbon atom lacking an octet, which makes it much less important than the other two.
Page 2
5. Draw the Lewis structure of each formula, including all possible resonance structures. Then draw the resonance
hybrid, making obvious differences in partial charge.
Problem
a. HCO2
−
(18 val e )
O
H
H
(HOCO2−)
O
O
O
C
H
O
O
O
C
H
H
O
(equal major)
c. CH2OH+
δ−
O δ−
δ+
O
C
C
H
O
δ−
O
(very minor)
(12 val e−)
H
H
C
O
(24 val e−)
C
(equal major)
C
(very minor)
O
O
H
O
(equal major)
O
H
C
O
(equal major)
b. HCO3−
H
C
O
O δ−
O
O
C
O
Resonance Hybrid
−
H
O
H
C
H
H
O
H
δ+ C
H
O
H
δ+
(major)
(24 val e−)
d. CH3NO2
H
H
C
H
O
N
H
O
H
H
N
H
C
N
H
H
C
H
C
N
C
H
(major)
C
δ− C
N
δ−
N
H
~2.5 bonds
(very minor)
H
H
H
C
(22 val e−)
f. CH3CNO
C
O δ−
(16 val e−)
H
H
N
(equal major)
H
C
C
H
O
H
(equal major)
e. CH2CN–
C
O δ−
H
O
H
C
N
O
H
C
H
C
N
H
(major)
O
H
C
H
C
N
H
(very minor)
O
C
H
δ−
δ−
C
N
O
~2.5 bonds
Page 3
6. The bond length of the C-O and C=O bond in the acetate ion (below) are equal. Explain this phenomenon,
using structures with your answer.
O
O
H3C
C
H3C
O
C
H3C
O
O
Res. hybrid:
C
O
O δ−
H3C
C
O δ−
The acetate ion has two equal energy resonance structures that equally contribute to the resonance hybrid.
There isn’t a C-O and C=O which would lead to different bond lengths. The actual structure is an average of
the resonance structures, and each C-O is a 1.5 bond, of equal length in between the length of a single and
double C-O bond.
7. In both structures shown below the negative charge is on a nitrogen atom, but the second structure is lower in
energy. Explain, using structures with your answer.
O
O
H3C
N
H
H
C
N
C
H
H
O
N
H
H
C
N
H
The right structure has RESONANCE – which spreads the negative charge out over two atoms (N,O) in the
molecule. Resonance is always a stabilizing effect, and charge dispersal (delocalization) is always better than
having a point charge located on only one atom. Resonance makes the 2nd structure lower energy, and more
stable.
HYBRIDIZATION AND ORBITAL DIAGRAMS
8. For each atom that is pointed to, identify the electron geometry, bond angles and hybridization of the atom.
a.
b.
c.
O
CH3 O
CH3
H
C
C
C
CH3 CH2
H
CH3
tetrahedral, 109.5˚, sp3
d.
linear
180˚, sp
e.
CH2
C
f.
O
CH2
CH3
linear, 180˚, sp
tetrahedral, 109.5˚, sp3
trigonal planar
120˚, sp2
S
O
CH3
CH3
tetrahedral, 109.5˚, sp3
trigonal planar tetrahedral
120˚, sp2
109.5˚, sp3
Page 4
9. Draw an orbital diagram of each ion below using atomic and hybrid orbitals (assume all atoms are hybridized
that can be). Label each orbital as s, p, sp, sp2 or sp3.
H
a.
H
C
C
H
H
H
H
b.
N
H
C
C
C
C
H H
10. Identify the orbitals involved in each designated bond (or bonds). Assume all atoms that can hybridize do so.
Label each bond as a sigma (σ) or pi (π).
a.
O
b.
O
c.
HO
σ "Csp2 – Osp2
σ "Csp2 – Csp2
π " Cp – Op
π " Cp – Cp
σ
Csp3 – Osp3
OH
σ: Csp3 – Csp2
Page 5
LINE STRUCTURES AND CONDENSED FORMS
11. Fill in the boxes with the correct depictions of each molecule.
Lewis structure
H
Condensed Form
(CH3)3CCH2CH(CH3)2
H
H C H H C H
H
H
H C
H
C
or
CH3C(CH3)2CH2CH(CH3)2
H
C
C
C H
H
H C H
H
H
H
H
C
C
C
H
or
or
CH3C(CH3)2CH2CH(CH3)CH3
H
H
Line Structure
Br
CH2=CHCH2Br
Br
H
H
H
C
C
C
H
H
C
N
N
C
H
HH
H
C
H
H
C
C
O
H
OH
H C
C
H
C
C
H
H
H
H
H
N
H
C
C
C
H C
H
H
C
H
C
NH2
H
H
H
CH
C
C(NH2)(CH2CH3)CH3
(triple bonds are linear!)
H
H
12. Permethrin is a topical cream for the treatment of scabies (a parasitic mite that burrows under the host’s skin
and causes intense itching). What is the molecular formula of Permethrin?
O
Cl
O
O
Cl
H3C
CH3
C: 21
H: 20
Cl: 2
O: 3
Page 6