Chemistry 120
Take Home Exam 2 Due November 9, 2011 ( Before class)
Name ___________________________
Instructions: Give answers in the space provided. Show calculations where required.
1. Complete the following Table by giving the required information in the space provided (8 marks)
Molecular
formula
Lewis structure
Electron domain
geometry
Molecular
geometry
Polarity
Eg
H2O
..
H-O-H
..
Tetrahedral
Bent
Polar
A
SF4
B
COCl2
C
CO32 –
D
PO2+
2. A pre-medical student was asked on the MCAT to give the trend of the Nitrogen-Oxygen bond
lengths in NO2⊕, NO2Ө, and NO3Ө in decreasing order (from shortest to longest) The answer given
was the following: (4 marks)
NO3–
>
Strongest
(shortest distance)
NO2–
>
NO2+
Weakest
(longest distance)
Use Lewis structure and resonance theory to justify whether the answer given is correct or incorrect.
Explain
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Chemistry 120
Take Home Exam 2 Due November 9, 2011 ( Before class)
3. For the following molecules give the Lewis structure, all possible resonance structures, and the
formal charges for all the atoms. The molecules are linear and bolded atom is central atom (6 marks)
a)
N3 –
b) SCN–
For the resonance structures given above which is the major contributor to the “true” structure.
4. Assign formal charges to the (O and S) atoms in the following resonance forms of H2SO3 (3 marks).
O
O
HO
S
A
OH
HO
S
OH
B
Which of these two structures is the more important contributor to the “true” structure?
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Chemistry 120
Take Home Exam 2 Due November 9, 2011 ( Before class)
5. The molecule pictured below is epinephrine, a compound used as a bronchodilator and antiglaucoma
agent (7 marks)
H
A
H
O
H
B
C
C
C
C
C
C
O
C
D
H
H
H
E H
C
C
N
C
H
H
..
H
H
H
H
a) Give the approximate bond angles for the positions labeled A-E
b) Which of these positions are the most polar?
6. For the following molecules, give the molecular shape and the expected bond angle (6 marks).
a)
CH3+
(H-C-H angle)
b) SF3+
(
F-S-F angle)
c) N2H2 (symmetrical)
(H-N-N angle)
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Chemistry 120
Take Home Exam 2 Due November 9, 2011 ( Before class)
7. Explain the following observation:
Cyclohexane (A) is a substance that contains a six-member ring of carbon atoms. The structure is
observed to be a puckered nonplanar shape. However the benzene ring (B) is also a six-member
ring of carbon atoms, but the structure is flat rather than puckered. (4 marks)
H
H
H
H
H
H
C
H
C
C
C
H
C
C
H
C
H
H
C
C
H
H
H
H
C
H
H
H
C
H
H
H
H
H
H
A
side view
H
H
H
C
H
C
C
C
C
H
C
C
C
H
C
H
H
H
C
C
C
H
H
H
B
side view
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Chemistry 120
Take Home Exam 2 Due November 9, 2011 ( Before class)
8
Vitamin C (Ascorbic acid) has the following connections among atoms. Complete the Lewis
electron dot-structure for Vitamin C, and indicate the number of sigma (σ) bonds and the number of
pi (π) bonds. Place an asterisk (*) next to the pi (π) bond. (Do not add atoms) (3 marks)
H
H
H
O
O
C
C
H
H
C
C
O
O
C
C
O
O
H
H
H
9. What hybridization do you expect for atoms that have the following number of electron
domains (2 marks)
a)
Three electron domains
b) Six electron domains
10 Give the expected hybridization for each of the underlined atoms in the following molecules
(3 marks):
a)
BrO3+
b)
CH3+
c)
SO3
5
Chemistry 120
Take Home Exam 2 Due November 9, 2011 ( Before class)
11. Give all possible Lewis structures for the odd electron molecule NO2 (nitrogen dioxide) – no charge.
Then give the molecule that represents the true structure. What is the bond order (6 marks)
-end of exam-
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