First Hour Exam 1999
Name:____________
(4 points)
Please show all work for partial credit
1. (18 points) Draw Lewis structures for the following compounds
HCN
PH3
PCl2-
PF5
F
F P F
F F
BH3
H
H BH
ClF5
2
2. (18 points) Draw at least 2 non-equivalent resonance forms for each of the following
molecules and evaluate the formal charge of each atom in each structure. Which is the
“best” structure.
ClO3-
O
O Cl
O
F.C. -Worst
Cl 7-5 =+2
-O 6-7 = -1
O
O Cl
O
Better
Cl 7-6 = +1
-O 6-7 = -1
=O 6-6=0
O
O Cl
O
Best
Cl 7-7 =0
-O 6-7 = -1
=O 6-6=0
NO3You can move the double bond around, but these structures
are considered equivalent. N may not exceed its octet so you can’t
move into none equivalent structures
FC. N = 5-4 = +1, -O 6-7 = -1, =O 6-6=0
SO3-2
O
O S
O
F.C. Bad
S 6-5 = +1
-O 6-7 = -1
O
O S
O
Best
S 6-6 = 0
-O 6-7 = -1
=O 6-6=0
O
O S
O
Not as good
S 6-7 = -1
-O 6-7 = -1
=O 6-6=0
3
3. (12 points) Write the Lewis structures and determine the molecular structure, bond
angles, and polarity of the following compounds
SeO3-2
KrF2
O
O S
O
Molecular Structure : linear
Bond Angles: 180o
Polarity : non-polar
Plus lots of resonance structures
Molecular Structure : trigonal pyramid
Bond Angles: <109o
Polarity : Probably polar
SbF5
I
F
6
+
F
F Sb F
F F
Molecular Structure : trigonal bipyramid
Bond Angles: 90o & 120o
Polarity : non-polar
Molecular Structure : octahedral
Bond Angles: 90o
Polarity : nonpolar
4
4. ( 12 points) Determine the Lewis structure, the hybridization of the central atom, and the
bond angles in the following molecules
TeF4
CF4
F
F
Te
F
F
dsp2
<90 & <120
sp3
109
XeOF4
NF3
d2sp3
<90
sp3
<109
5. (12 points) Using molecular orbital theory determine the Bond Order for the following
diatomic species. If the species is stable, determine whether it is paramagneitc or
diamagnetic.
C22_
F2p*
_ _ B2p*
89 F2p
89 89 B2p
89 F2s*
89 F2s*
CN+
_
F2p*
_ _ B2p*
_
F2p
89 89 B2p
89 F2s*
89 F2s*
N2+
B.O = (8-2)/2 =3
All paired diamagnetic
B.O = (6-2)/2 =2
All paired diamagnetic
_
F2p*
_ _ B2p*
8_ F2p B.O = (9-2)/2 =2.5
89 89 B2p 1 unpaired paramagnetic
89 F2s*
89 F2s*
F2289 F2p*
89 89 B2p*
89 89 B2p B.O =0 unstable
89 F2p
89 F2s*
89 F2s*
5
6. (12 points) Draw the structure of the following compounds
2,2,4-trimethylhexane
3
none
ne
C-C-C=C-C-C-C-C-C
1
methylcyclopropane
2
,
3
m
ethylethyl-1-octene
7. (12 points) Name the following compounds
CH3
CH2
CH3
CH C
CH3
CH
CH3
CH
CH3
CH3
CH2
CH2
CH3
3-methyl-1-pentyne
C
CH2
C
CH2
CH2
CH3
CH3
3-ethyl-3,5,5,8-tetramethylnoname
6
2,5-dimethyl-2,4-heptadiene
CH3
C
CH3
CH CH C
CH2
CH3
1 ethylcyclopentene
CH3
CH2
CH3
7
8. (5 points Extra Credit) Karl O. Christe recently synthesized N5+. This is the first new
species that contains only nitrogen to be synthesized in the last 100 years. It is only
marginally stable and is highly explosive. Find a reasonable Lewis structure for N5+ and
describe its molecular shape and geometry. To get you started on the right track I will tell
you that it is a non-branched chain of N atoms and does not contain any ring structures.