Exam III – Key (Answers on last page)
All notes, books, etc., must be placed out of sight. Please read each of the problems carefully. If
something is not clear, please ask.
The exam consists of 37 problems on 5 pages with some extra credit opportunities on the sixth
page. Make sure your exam is complete. The exam is worth 100 points with each of the
problems labeled as to its point value. Please print your name on both the exam copy and the
ScanTron® answer sheet.
Answers to the multiple choice are to be placed on the ScanTron® sheet. Other answers should
be placed in the space provided and written legibly. If I cannot read it -- it is wrong. You MUST
show your work clearly for the problems indicated in order to receive full credit. Please include
an explanation whenever asked to or whenever necessary to make your answer clear. If I cannot
understand it -- it is wrong. Please put your name on every page of the exam.
There are scratch papers and periodic tables available for your use. If you require data, please
As usual, no cheating is allowed. Good Luck!
Chemistry 1211 Exam III Page 1 Name__________________________________
The first part of the exam consists of 36 multiple choice questions. Please put your final answers
on the ScanTron® answer sheet. You may write on the exam, but only the answer sheet answer
will count for the multiple choice questions. Each of these is worth 2½ points.
1. Atomic radius generally increases as we move…
a. down a group and from right to left across a period
b. up a group and from left to right across a period
c. down a group and from left to right across a period
d. up a group and from right to left across a period
e. down a group; the period position has no effect
2. Of the choices below, which give the correct order for first ionization energies?
a. Cl > S > Al >Ar > Si b. Ar > Cl > S > Si > Al c. Al > Si > S > Cl > Ar
d. Cl > S > Al > Si > Ar e. S > Si > Cl > Al > Ar
3. Consider the general valence electron configuration of ns2np5 and the following statements:
(i) elements with this electron configuration are expected to form -1 anions
(ii) elements with this electron configuration are expected to form +1 cations
(iii) elements with this electron configuration are nonmetals
(iv) elements with this electron configuration belong to Group VII (same as 17)
Which statements are true?
a. (i) and (ii) b. (i), (ii), and (iii) c. (ii) and (iii) d. (i), (iii), and (iv) e. all are true
4. For the ion NO¯ , how many electrons are considered for a Lewis dot structure?
a. 15 b. 14 c. 11 d. 10 e. 12
5. Which of the following molecules has a square planar molecular geometry?
a. CCl4 b. XeF4 c. PH3 d. XeF2 e. ICl3
6. The type of compound that is most likely to contain a covalent bond is…
a. one that is composed of a metal from the far left of the periodic table and a nonmetal
from the far right of the periodic table.
b. a solid metal
c. one that is composed of only nonmetals
d. held together by the electrostatic forces between oppositely charge ions
e. there is no general rule to predict covalency in bonds
Chemistry 1211 Exam III Page 2 Name__________________________________
7. The F-N-F bond angle in the NF3 molecule is expected to be…
a. 90° b. 109.5° c. 120° d. slightly less than 109.5° e. slightly less than 120°
8. The molecular geometry of the BrO3¯ ion is…
a. trigonal pyramidal b. trigonal planar c. bent d. tetrahedral e. T-shaped
9. According to VSEPR theory, if there are two electron domains on a central atom, they will be
arranged such that the angles between the domains are…
a. 360° b. 120° c. 109.5° d. 180° e. 90°
10. Of the molecules below, which one is polar?
a. SbF5 b. AsH3 c. I2 d. SF6 e. CH4
11. Using the VSEPR model, the molecular geometry of XeF2 is…
a. linear b. trigonal planar c. tetrahedral d. bent e. trigonal pyramidal
12. Of the following, which gives the correct order for atomic radius for: Mg, Na, P, Si, and Ar?
a. Mg > Na > P > Si > Ar b. Ar > Si > P > Na > Mg c. Si > P > Ar > Na > Mg
d. Na > Mg > Si > P > Ar e. Ar > P > Si > Mg > Na
13. Which of the following would you expect to have the largest second ionization energy?
a. Si b. Mg c. Al d. Na e. P
14. Which ion below has the largest radius?
a. Cl¯ b. K+ c. Br¯ d. F¯ e. Na+
15. How many single covalent bonds must a silicon atom form to have a complete octet in its
a. 3 b. 4 c. 1 d. 2 e. 0
16. What is the maximum number of double bonds that a carbon atom can form?
a. 4 b. 1 c. 0 d. 2 e. 3
Chemistry 1211 Exam III Page 3 Name__________________________________
17. The nitrate ion, NO3¯, has three resonance structures. What is the formal charge on the
nitrogen in these structures?
a. -1 b. 0 c. +1 d. +2 e. -2 f. other
18. Which of the following has the bonds correctly arranged in order of increasing polarity?
a. Be-F < Mg-F < N-F < O-F b. O-F < N-F < Be-F < Mg-F
c. O-F < Be-F < Mg-F < N-F d. N-F < Be-F < Mg-F < O-F
e. Mg-F < Be-F < N-F < O-F
19. Why don’t we draw double bonds between the Be atom and the Cl atoms in BeCl2?
a. the would give a positive formal charge to the chlorine atoms and a negative formal
charge to the beryllium atom
b. there aren’t enough electrons
c. that would result in more than eight electrons around the beryllium atom
d. that would result in more than eight electrons around each chlorine atom
e. that would result in the formal charge not adding up to zero
20. According to VSEPR theory, if there are five electron domains in the valence shell of an
atom, what will be the expected electron domain geometry?
a. octahedral b. linear c. tetrahedral d. trigonal planar e. trigonal bipyramidal
21. The molecular geometry of the PHCl2 molecule is…
a. bent b. trigonal planar c. trigonal pyramidal d. tetrahedral e. T-shaped
22. The O-C-O bond angle in the CO32- is approximately…
a. 90° b. 109.5° c. 120° d. 180° e. 60°
23. The central Xe atom in the XeF4 molecule has __?__ unbonded electron pairs and __?__
bonded electron pairs in its valence shell.
a. 1, 4 b. 2, 4 c. 4, 0 d. 4, 1 e. 4, 2
24. Of the molecules listed below, which is nonpolar?
a. BF3 b. NF3 c. IF3 d. PBr3 e. BrCl3
Chemistry 1211 Exam III Page 4 Name__________________________________
25. Which isoelectronic series is correctly arranged in order of increasing radius?
a. K+ < Ca2+ < Ar < Cl¯ b. Cl¯ < Ar < K+ < Ca2+ c. Ca2+ < Ar < K+ < Cl¯
d. Ca2+ < K+ < Ar < Cl¯ e. Ca2+ < K+ < Cl¯ < Ar
26. How many resonance forms can be drawn for CO32- ion? (carbon is central atom)
a. 1 b. 2 c. 3 d. 4 e. 0
Consider the following electron configurations to answer questions 27 & 28.
(i) 1s22s22p63s1 (ii) 1s22s22p63s2 (iii) 1s22s22p63s23p1
(iv) 1s22s22p63s23p4 (v) 1s22s22p63s23p5
27. The electron configuration belonging to the atom with the highest second ionization energy
a. (i) b. (ii) c. (iii) d. (iv) e. (v)
28. The electron configuration belonging to the atom with the highest first ionization energy is…
a. (i) b. (ii) c. (iii) d. (iv) e. (v)
29. Sodium is much more apt to exist as a cation than is chlorine. This is because…
a. chlorine is a gas and sodium is a metal
b. chlorine is in the same period of the periodic table as sodium
c. chlorine is bigger than sodium
d. chlorine has a greater ionization energy than sodium does
e. chlorine is more metallic than sodium
30. In the molecule CFClBrI (carbon the central atom), which atom has the largest partial
a. Cl b. F c. Br d. I e. C f. all are equal in their charge
31. The electron-domain geometry and molecular geometry of iodine trichloride are __?__ and
a. trigonal bipyramidal, trigonal planar b. tetrahedral, trigonal pyramidal
c. trigonal bypyramidal, T-shaped d. octahedral, trigonal planar
e. T-shaped, trigonal planar
Chemistry 1211 Exam III Page 5 Name__________________________________
32. In which of the molecules below is the carbon – carbon distance the shortest?
a. H2C=CH2 b. H-C≡C-H c. H3C 3
CH d. H2C=C=CH2 e. H3C 2 3
Consider the following species for the next question.
(i) PCl3 (ii) CCl4 (iii) TeCl4 (iv) XeF4 (v) SF6
33. For which of the above molecules is the molecular geometry (shape) the same as the VSEPR
electron domain geometry?
a. (i) and (ii) b. (i) and (iii) c. (ii) and (v) d. (iv) and (v) e. (v) only
34. Three monosulfur fluorides are observed: SF2, SF4, and SF6. Which are polar?
a. SF2 only b. SF2 and SF4 only c. SF4 only d. SF6 only e. all three are
35. Of the bonds C – N, C = N, and C ≡ N, the C – N bond is the…
a. strongest and shortest b. strongest and longest c. weakest and shortest
d. weakest and longest e. intermediate in both strength and length
36 The best thing about this class is…
a. Dr. Braun a. 12:50 pm a. it is almost over a. the TEXT a. everything!
37.(10) Answer this directly on this exam paper: The reaction below is used to make methanol:
CO (g) + 2 H2 (g) CH3OH (l) ∆H = -128 kJ
(triple bond) (all single bonds)
Bond C≡O H–H C–O O–H
Using the data shown in this Table, and showing Energy 1072 436 358 463
all of your work clearly, calculate the C – H (kJ/mole)
Bonds Made (-) Bonds Broken (+)
3 (C-H) = 3x 1 (C≡O) = 1072
1 (C-O) = 358 2 (H-H) = 2 (436)
1 (O-H) = 463
-(821 + 3x)
1944 – (821 + 3x) = -128 x = 417 kJ/mole
Extra Credit #1: The accepted value for the C – H bond energy is 413 kJ/mole. Explain briefly
Chemistry 1211 Exam III Page 6 Name__________________________________
why your answer to #37 is different than this value.
Bond energies are average values and only approximate real systems.
Extra Credit #2: A secretary types four letters to four people and addresses the four envelopes.
If she inserts the letters at random, each in a different envelope, what is the probability that
exactly three letters will go into the correct envelope? List your answer as a percentage. _zero__
Extra Credit #3: Consider:
When Oxygen U played Hydrogen Tech Little Willie was a chemist
The game had just begun. Little Willie is no more
Hydrogen racked up two quick goals, For what he thought was H2O
And Oxygen still had none. Was H2SO4!
Then Oxygen scored a single goal,
And thus it did remain:
Hydrogen two, Oxygen one,
Called, because of rain!
Write me a poem about chemistry for some extra points.
1. a 2. b 3. d 4. e 5. b 6. c 7. d 8. a 9. d
10. b 11. a 12. d 13. d 14. c 15. b 16. d 17. c 18. b
19. a 20. e 21. c 22. c 23. b 24. a 25. d 26. c 27. a
28. e 29. d 30. b 31. c 32. b 33. c 34. b 35. d 36. a
Answers to the written problems are under the problem above.