Name: 1: /33Grade: /100 2: /33
3: /33+1 point
Midterm Exam 2CHEM 181: Introduction to Chemical Principles
October 13, 2015
Directions:
Do all three problems.
Show all of your work neatly and clearly. Do not skip steps. Partial credit will beawarded for all problems. Correct answers will not receive credit if your work is notshown.
If you are not sure exactly what a question means, ask!
Not all problems are of equal difficulty, but all are worth the same fraction of theoverall grade.
1
1. Draw Lewis structures for the isomers with the molecular formula C3H3NO2 thatare shown on the following pages. For each isomer shown, do the following:
• Label non-zero formal charges.
• Include all resonance structures that follow the octet rule.
• Label each resonance structure as either major, minor, very minor, ornot valid (i.e., should not be considered).
• Rank the resonance structures in numerical order (1=best, 2=next best,etc.) If two structures are exactly equivalent, give them the same number.
(a) Methyl cyanoformate is an isomer of C3H3NO2, with the connectivityshown below:
CH
H
H
O C
O
C N
Provide a Lewis structure for methyl cyanoformate.
2
(b) Acetyl isocyanate is an isomer of C3H3NO2, with the connectivity shownbelow:
C
H
H
H
C
O
N C O
Provide a Lewis structure for acetyl isocyanate.
3
(c) Oxazolone is an isomer of C3H3NO2, with the connectivity shown below:
N C
OC
C
O
H
H
HProvide a Lewis structure for oxazolone.
4
2. Here is the best single electron-dot structure for acetyl azide (C2H3N3O):
H C
H
H
C
O
N N N
Consider the following proposed (but not necessarily correct) resonance struc-tures, labeled A through E. Categorize each one according to the following.(You will not receive credit for categorizing a structure if you do not provide anexplanation.)
H C
H
H
C
O
N N N
H C
H
H
C
O
N N N
H C
H
H
C
O
N N NH C
H
C
O
N N N
H C
H
H
C
O
N N N
H
A B C
D E
(a) Which structures (if any) must be included as resonance structures becausethey tell you something new about the molecule? Identify each structureby its label, and explain (one sentence each) what is important about its in-clusion (i.e., its effect on bond order, formal charge, and/or hybridization).
5
(b) Which structures (if any) could be included, but are very minor and theirinclusion would not change bond order, formal charge, or hybridization inany significant way. Identify each structure by its label, and explain (onesentence each) what makes the structure unimportant.
(c) Which structures (if any), are bad structures that can not be included.Identify each structure by its label, and explain (once sentence each) theproblem or problems with it.
6
3. Draw 4 isomers that have the molecular formula C2H3NO. Do not use rings.
(a) For each isomer, provide a Lewis structure with major and minor resonancestructures and non-zero formal charges (if present).
7
(b) Label which of the four isomers you expect to be the most stable compound(“most” or “most stable”) and explain (1 sentence):
(c) Label which of the four isomers you expect to be the second most stablecompound (“second most” or “second”) and explain (1 sentence):
(d) Label which of the four isomers you expect to be the third most stablecompound (“third most” or “third”) and explain (1 sentence):
(e) Label which of the four isomers you expect to be the least stable compound(“least” or “least stable”) and explain (1 sentence):
8
Electronegativity:
Atom χ
F 3.98O 3.44Cl 3.16N 3.04Br 2.96I 2.66S 2.58C 2.55H 2.20
Equations:Bond order = 1
2(# bonding electrons−# antibonding electrons).
Formal charge = # valence electrons−(# lone pair electrons+ 1
2# bonding electrons
)
9
The
Peri
odic
Tab
le o
f the
Ele
men
ts1 H
Hyd
roge
n1.
0079
4
2 He
Hel
ium
4.00
3
3 Li Lith
ium
6.94
1
4 BeBe
rylli
um9.
0121
82
5 B Bor
on10
.811
6 C Car
bon
12.0
107
7 NN
itrog
en14
.006
74
8 OO
xyge
n15
.999
4
9 FFl
uorin
e18
.998
4032
10 Ne
Neo
n20
.179
7
11 Na
Sodi
um22
.989
770
12 Mg
Mag
nesiu
m24
.305
0
13 Al
Alu
min
um26
.981
538
14 Si Silic
on28
.085
5
15 PPh
osph
orus
30.9
7376
1
16 S Sulfu
r32
.066
17 Cl
Chlo
rine
35.4
527
18 Ar
Arg
on39
.948
19 KPo
tass
ium
39.0
983
20 Ca
Calc
ium
40.0
78
21 ScSc
andi
um44
.955
910
22 TiTi
tani
um47
.867
23 VV
anad
ium
50.9
415
24 Cr
Chr
omiu
m51
.996
1
25 Mn
Man
gane
se54
.938
049
26 Fe Iron
55.8
45
27 Co
Coba
lt58
.933
200
28 Ni
Nic
kel
58.6
934
29 Cu
Cop
per
63.5
46
30 Zn Zinc
65.3
9
31 Ga
Gal
lium
69.7
23
32 Ge
Ger
man
ium
72.6
1
33 As
Ars
enic
74.9
2160
34 SeSe
leni
um78
.96
35 Br Brom
ine
79.9
04
36 Kr
Kry
pton
83.8
037 R
bR
ubid
ium
85.4
678
38 SrSt
ront
ium
87.6
2
39 YY
ttriu
m88
.905
85
40 ZrZi
rcon
ium
91.2
24
41 Nb
Nio
bium
92.9
0638
42 Mo
Mol
ybde
num
95.9
4
43 TcTe
chne
tium
(98)
44 Ru
Rut
heni
um10
1.07
45 Rh
Rho
dium
102.
9055
0
46 Pd Palla
dium
106.
42
47 Ag
Silv
er10
7.86
82
48 Cd
Cad
miu
m11
2.41
1
49 In Indi
um11
4.81
8
50 Sn Tin
118.
710
51 SbA
ntim
ony
121.
760
52 TeTe
lluriu
m12
7.60
53 IIo
dine
126.
9044
7
54 Xe
Xen
on13
1.29
55 Cs
Ces
ium
132.
9054
5
56 Ba Bariu
m13
7.32
7
57 LaLa
ntha
num
138.
9055
72 Hf
Haf
nium
178.
49
73 Ta Tant
alum
180.
9479
74 WTu
ngste
n18
3.84
75 Re
Rhe
nium
186.
207
76 Os
Osm
ium
190.
23
77 Ir Iridi
um19
2.21
7
78 PtPl
atin
um19
5.07
8
79 Au
Gol
d19
6.96
655
80 Hg
Mer
cury
200.
59
81 TlTh
alliu
m20
4.38
33
82 Pb Lead
207.
2
83 Bi Bis
mut
h20
8.98
038
84 PoPo
loni
um(2
09)
85 At
Asta
tine
(210
)
86 Rn
Rad
on(2
22)
87 FrFr
anci
um(2
23)
88 Ra
Rad
ium
(226
)
89 Ac
Act
iniu
m(2
27)
104
Rf
Rut
herf
ordi
um(2
61)
105
Db
Dub
nium
(262
)
106
SgSe
abor
gium
(263
)
107
Bh Bohr
ium
(262
)
108
Hs
Has
sium
(265
)
109
Mt
Mei
tner
ium
(266
)
110
(269
)
111
(272
)
112
(277
)
113
114
58 Ce
Ceriu
m14
0.11
6
59 PrPr
aseo
dym
ium
140.
9076
5
60 Nd
Neo
dym
ium
144.
24
61 PmPr
omet
hium
(145
)
62 Sm Sam
ariu
m15
0.36
63 Eu Euro
pium
151.
964
64 Gd
Gad
olin
ium
157.
25
65 Tb Terb
ium
158.
9253
4
66 Dy
Dys
pros
ium
162.
50
67 Ho
Hol
miu
m16
4.93
032
68 Er Erbi
um16
7.26
69 Tm Thul
ium
168.
9342
1
70 Yb
Ytte
rbiu
m17
3.04
71 Lu Lute
tium
174.
967
90 Th Thor
ium
232.
0381
91 PaPr
otac
tiniu
m23
1.03
588
92 UU
rani
um23
8.02
89
93 Np
Nep
tuni
um(2
37)
94 PuPl
uton
ium
(244
)
95 Am
Am
eric
ium
(243
)
96 Cm
Cur
ium
(247
)
97 BkBe
rkel
ium
(247
)
98 Cf
Calif
orni
um(2
51)
99 EsEi
nste
iniu
m(2
52)
100
Fm Ferm
ium
(257
)
101
Md
Men
dele
vium
(258
)
102
No
Nob
eliu
m(2
59)
103
LrLa
wre
nciu
m(2
62)
1995
IUPA
C m
asse
s and
App
rove
d N
ames
from
http
://w
ww
.che
m.q
mw
.ac.
uk/iu
pac/
AtW
t/m
asse
s for
107
-111
from
C&
EN, M
arch
13,
199
5, p
. 35
112
from
http
://w
ww
.gsi.
de/z
112e
.htm
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