CHEM 1411 Practice Exam #3
Name:_________________
(Chapters 9,10 & 11)
Score:
Part I- ( 2 points each) - Please bubble your correct answer in scantron
DO NOT CIRCLE
1. How many unpaired electrons are in the Lewis dot symbol of
a chlorine atom?
A. 7
B. 1
C. 5
D. 3
2. Which one violates octet rule stability ?
A. S2-
B. Mg+
C. O2-
D. Fr+
3. Which one of the following forms an ionic bond with Chlorine
gas?
A. C
B. Mg
C. P
D. As
4. How many valence electrons are in SO42- ion?
A. 32e-
B. 30e-
C. 14e-
D 28e-
5. What is the formal charge on sulfur in the following molecule?
O
H
O
S
O
H
O
A. +3
B. +2
C. – 1
D. 0
6. In which one of the following molecules one atom do not follow octet rule?
A. SO2
B. CO2
C. CO32-
D. NO
7. Which one of the following molecules has resonance structures?
A. CO
B. CO2
C. CO32-
D. Non
8. In which one of the following molecules the central atom has expanded
octet?
A. BF3
B. BeH2
C. SF6
D. NO
9. Arrange the following bonds according to their increasing bond energies
A. C
C>C
C>C
C
B. C
C> C
C>C
C
C. C
C<C
C<C
C
D. C
C< C
C<C
C
10. Which of the following molecules has an ionic bond (The electronagativities
are Cs = 0.7, H = 2.1, S = 2.5, Cl = N = 3)
A. NH3
B. H2S
C. CsCl
D. N2
11. The electronagativities
A. Increase from bottom to top in a group
B. Decrease from left to right in a period
C. A & B
D. Non
12. Based on the reactivity of the elements, which one of the following is right
A. Li>Na>K>Rb>Cs
C. F>Cl>Br>I
B. Cs>Rb>K>Na>Li
D. B &C
13. What is the electron pair geometry of H2O
A. Octahedron
B. Tetrahedron
C. Linear
14. What is the molecular geometry of I3A. trigonal bipyramidal
C. T-Shap
B. Trigonal pyramidal
C. Linear
15. Determine the total number of sigma and pi bonds in the
following molecular structure.
H - C  C- O- C = C - C  C-H


H H
C. 10 σ , 5 π
D. none of these
C. Bent
16. Which of the following molecules considered to be a polar
molecule?
A. NH3
B. BF3
C. CO2
D. C2H2
17. Which of the following molecules has a higher dipole moment
Br
Br
Br
C
H
C
C
H
H
C
Br
H
1
2
A. 1
B. 2
C. 1 and 2 have same dipole moment
D. None of the above molecules has a dipole moment
18. What is the hybridization in N3A. sp
B. sp2
C. sp3
D. sp3d
19. Which of the following molecules is linear
A. H2O
B. NH3
C. CO2
D. SO2
20. What are the hybridization and the approximate bond angle in
CS2 (C is the central atom) ?
A. sp2, 1070
B. sp3, 1200
C. sp2, 1200
D. sp, 1800
21. The electron-pair geometry and molecular geometry of
Boron trichloride (BCl3) are ------ respectively
A. tetrahedral,tetrahedral
B. tetrahedral, trigonal planar
C. trigonal planar, trigonal planar
D. tetrahedral, trigonal pyramidal
22. In a body centered cubic lattice, how many atoms will be there in a unit cell
A. 1
B. 2
C. ½
D. 4
23. Which of the following molecules do not exist?
A. H2
B. O2
C. He2
D. Cl2
24. When the Lewis electron-dot formula for SF4 is drawn, how many
non-bonding pairs (lone pairs) of electrons are on the sulfur atom?
A. 0
B. 1
C. 2
d) 3
25. Which of the following molecules can form a hydrogen bond?
A. SiH4
B. C2H5OH
C. H2Te
D. CH4
26. Nonpolar substances will condense mainly because of
A. Permanent dipole-dipole interactions
C. Dispersion forces
B. electrical forces
D. hydrogen bonds
27. Arrange CH4, CF4, CCl4, CBr4, CI4molecules in the order of increasing
melting points
A. CH4>CF4>CCl4>CBr4>CI4
B. CH4<CF4<CCl4<CBr4<CI4
C. CI4>CBr4>CCl4>CF4>CH4
D. CI4<CBr4<CCl4<CF4<CH4
28. What type(s) of intermolecular forces exist between I2 and NO3A. Ion induced dipole forces and dispersion forces
B. Dipole-dipole induced forces only
C. Ion induced dipole forces only
D. Dispersion forces only
29. The hydrides of group 6A elements are H2O, H2S, H2Se, and H2Te.
Which one of these has highest boiling point?
A. H2O
B. H2S
C. H2Se
D. H2Te
30. Some insects can walk on water because of the phenomenon, called
A. Viscosity
B. Surface tension
C. Velocity
D. A&C
31. Arrange the following molecules in order of increasing boiling points
1. CH3CH2OH
2. H2O
A. 1<2<3<4
B. 4<3<1<2
3. CH3OCH3
C. 2<3<1<4
4. CH3CH2CH3
D. 4<3<2<1
32. Diamonds are extremely stable owing to which of the following kinds of
bonding?
A. ionic bonding
B. network covalent bonding
C. hydrogen bonding D. Dispersion forces
33. Ice floats on water because of
A. London forces
C. Hydrogen bonding
B. Surface tension
D. Covalent bonding
34. Water rises in capillary tube because
A.
B.
C.
D.
Adhesion grater than cohesion
cohesion grater than adhesion
Cohesion and adhesion are same
Non of the above
35. Which theory supports the concept that O2 is a paramagnetic?
A. valance bond theory
B. crystal field theory
C. Molecular orbital theory D. Dalton’s atomic theory
PART II- ( 5 points each) Please show all your work.
36. Give the electron-pair geometry and molecular geometry of ClO337. Find out the bond orders of the following molecules
I. N2 II. CN- III) O2 IV) C2238. Draw Lewis dot (electron) structure for SO32- and determine
a) electron geometry
b) molecular geometry
c) hybridization
d) bond angle
39. Metallic iron crystallizes in a cubic lattice. The unit cell edge length is 287 pm.
The density of iron is 7.87 g/cm3. How many iron atoms are within a unit cell?
40. Write the resonance structures of CO32-
41. Calculate the enthalpy change for the following reaction
2H2 + O2  2H2O
(Bond energies in kj/mole: H-H=436.4., O-O=142., O-H=460)
Bonus (10 points)
I. Write all possible Lewis structures of PO4-3. Which one is most stable?
or
II. Which one of the following Lewis structures is most preferred for H2SO4 and
why?
O
O
H
O
S
O
H
H
O
O
S
O
O
H
Answer key:
1-B; 2-B; 3-B; 4-A; 5-B; 6-D; 7-C; 8-C; 9-C; 10-C; 11-A; 12-D; 13-B; 14-C, 15-C,
16-A, 17-A, 18-A, 19-C, 20-D, 21-C, 22-B, 23-C, 24-A, 25-B, 26-C; 27-B, 28-A,
29-A, 30-B, 31-B, 32-B, 33-C, 34-A, 35-C,
36. Draw the Lewis structure: electron pair geometry – tetrahedral
molecular geometry - trigonal pyramidal
37. Draw the MOT diagram for each molecule and distribute the electrons
bond order = ½(electrons in bonding molecular orbitals – electrons in antibonding molecular orbitals)
38. a) tetrahedran b) trigonal pyramidal c) sp3 d) 107.5
39. d=m/v
d = 7.87 g/cm3
v = (287 X 10-10cm)3 = 23639903 x 10-30 =2.364 x 10-23 cm3
m=dxv
m = 7.87g/cm3 x 2.364 x 10-23 cm3 = 1.86 x 10-22 g
Molar mass of Iron = 55.85 g
1.86 x 10-22 g x 6.023x1023 atoms
55.85g
= 2 atoms
40. Draw the Lewis structure and then resonance structures
41. Energy input-Energy output = enthalpy change
(2x436.4 + 142) – (4x460) = -825.2
Bonus:
I.
II.
Draw the most stable Lewis structure and calculate the formal charges
Calculate the formal charges; structure with least formal charges is
most prefered