Houston Community College System
Chemistry 1411, Fall 2010
EXAM # 3
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CHEM 1411 EXAM # 3
(Chapters 7, 8, 9, 10)
Name:______________________________
Score:
Directions- please answer the following multiple-choice questions next to each number. Please show all your work for
bonus question and part(2) questions in the space provided.
Part (1) - Multiple Choice - (3 points each)
_____ 1. How many unpaired valence electrons are in phosphorus atom?
A.7
B. 3
C. 5
D. 1
E.8
_____ 2. Which of the following molecules/ions is nonpolar?
A. HCN
B. HCl
C. CO2
D. NH3
E. SO2
_____ 3. Determine the total number of sigma and pi bonds in the following molecular structure.
H
H
O
C
C
C
H
C
H
C
C
C
C
C
A. 11 , 6 
H
B. 11 , 11 
C. 16 , 6 
H
D. 16 , 11 
E. none of these
D. SO4-
E. None of them
_____ 4. Which of the molecule has 3 resonance structures ?
A. SO2
C. PO3-
B. NH3
_____ 5. Which of the following molecules has the bond order 1 ?
A. O2
B. H2
C. H2-
D. He2
_____ 6. According Molecular orbital theory what is the correct statement about Oxygen
A. 2 unpaired electrons and diamagnetic
B. 1 Unpaired electron and paramagnetic
C. 2 unpaired electrons and paramagnetic
D. 0 Unpaired electrons, diamagnetic
E. None of them
_____ 7. What kind or hybridization you can see in H2C=CH2 and CCl4
A. sp and sp3
C. sp and sp2
B. SP2 and SP2
D. sp2 and sp3
E. Cannot guess
2
E. B2-
_____ 8. The configuration (σ1s)2(σ*1s)2 (σ2s)2(σ*2s)2 (π2p)2(π2p)2(σ2p)2 is the molecular orbital description for the
ground state of
A. Li2
B. B2
C. Be2
D. B22+
E. C22-
D. 9
E. 0
_____ 9. How many electrons are present in π2p* of N2 molecule
A. 1
B. 2
C. 3
_____ 10. Hydrogen bonding is predominant in the following molecules
A) H2S
B) CH2-CH2-O-H C) CH3-CH2-NH2
D) H3C-O-CH3
E) B and C
_____11. Which of the molecule has more than octet electrons in central atom?
A. NO2
B. SO2
C. CO2
D. PCl5
E. All of them
____ 12. Which one of the following ions has an octet of valence electrons?
i. Cl+
ii. Al+2
iii. Cs+
iv. I-
A. all of them
B. none of them
C. i & ii
D. iii & iv
E. ii alone
_____ 13. Choose the correct order of ionization energy of the atoms, Ba, Br, Bi?
A. Ba< Br < Bi
B. Br < Bi < Ba
C. Ba < Bi < Br
D. Br < Ba<Bi
E. Bi < Ba < Br
_____ 14. What are the hybridization and the approximate bond angle of CH4?
A. sp2, 104o
B. sp3, 109.5o
C. sp, 180o
D. sp3d, 900
E. sp3d2, 180o
_____ 15. The electron-pair geometry and molecular geometry of BH4- are respectively
A. Tetrahedral, tetrahedral
C. tetrahedral, trigonal pyramid
E. octahedral, square planar
B. tetrahedral, trigonal planar
D. trigonal bipyramidal, see-saw
_____ 16. Which of the following has bond order of 2?
I. F2-2
A. I & III
B. I & IV
II. NO-
III) O2
IV) N2
C. I only
D. III Only
E. II & III
_____ 17. Which of the following can be expected to have relatively high boiling point?
A. H-I
B. H-Br
C. H-Cl
D. H-F
3
E. O2
_____ 18. Which of the following atoms cannot accommodate an excess of 8 electrons in Lewis structures where
it is the central atom?
A. C
B. N
C. O
D. F
E. all of them
_____ 19. How many atoms/ions/molecules are assigned to Face centered cube
A. 4
B. 2
C. 3
D. 1
E. 6
_____20. Choose from the molecules listed below, the one with the weakest intermolecular force
A.
H2O
B. F2
C. H-Cl
D. Cl2
E. NH3
Part (2) - Show all your work. ( 8 points each)
21. Draw Lewis dot (electron) structure for SF6 and determine
a) Electron geometry
F
F
b) molecular geometry
c) polar or nonpolar
F
S
F
F
Octahedral
Non polar
F
Indicate 6 e- for each F
22. Use Molecular orbital theory to predict the following for NO- :
a) Its molecular orbital configuration
b) Its bond order
c) Is it paramagnetic or diamagnetic?
MO configuration (Same as N2 Model)
(Total valence electrons = 12)
----- σ*2p
------
------ π*2p
----- σ2p
------
Bond order
8 Bonding e4 Anti bonding e8-4/2 = 2
------ π2p
----- σ*2s
----- σ2s
4
Magnetism
Paramagnetic
23. The crystal of gold is Body centered cub. The edge length is 762 pm. Calculate the density of gold.
Mass: Number of gold atoms in BCC are 2, 1 Mole Au = 197.0 g = 6.02 x 1023 Au atoms
2 Au atoms x 197.0g Au/6.02 x 1023Au atoms = 6.544 x 10-22 grams Au
Volume: Length = 762 pm 1pm = 10-10 cm
762 pm x 10-10 cm/ 1pm = 7.62 x 10-8 cm
Volume = length3
(7.62 x 10-8 cm)3 = 4.42 x 10-22 cm3
Density = m/v
6.543 x 10-22g/4.42 x 10-22 cm3 = 1.48g/cm3
24. Draw all the resonance structures of the nitrate ion, NO3-
Follow the class notes to draw the dot structure:
The resonance structures: 3
25. Consider the following three resonance structures of the thiosulfate ion, S2O3-2.
a. Assign formal charges to all atoms in all three structures
b. Pick the major structure based on the formal charges. S is less electronegative than O.
..
..
:O:
:O:
:O-S-S:
..
..
:O:
..
Structure I
:O:
:O=S=S:
:O=S-S:
..
:O:
:O:
..
..
Structure II
Structure III
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