GENERAL CHEMISTRY EXAM NO.3
TOPICS: Covalent Bonding
I. Multiple Choice. Write your answers beside the each number. Use capital letters. Choose the letter of the best answer. (1 point each)
1. It is a pair of electrons that is shared between two atoms.
A. covalent bond D. an ionic bond
B. lone pair E. coordinate bond
C. double bond
2. All of the following Lewis structures of nitrogen oxides are possible EXCEPT
A. N2O.
B. N2O4.
C. N2O3.
D. N2O5.
E. All of the above are correct structures.
3. Formal charge is _________.
A. the absolute value of the charge on a polyatomic anion or cation.
B. the difference between the number of lone pairs of electrons and shared pairs of electrons on any atom in a Lewis structure.
C. the difference between the number of valence electrons and the number of protons in any given atom.
D. equal to the number of valence electrons in a free atom minus the number of shared in covalent bonds.
E. the difference between the number of valence electrons in a free atom and the number of electrons assigned to the atom in a Lewis structure
4. G. N. Lewis is well known for multiple contributions to the study of chemistry. Which of these below is attributed to Lewis?
A. covalent bonding D. hybridization
B. ionic bonding E. paramagnetism
C. VSEPR
5. What is the structure of SF6?
A. trigonal bipyramidal
B. square pyramidal
C. square planar
D. octahedral
E. cubic
6. This gas changed the perception of the reactivity of this group.
A. Oxygen
B. Xenon
C. Helium
D. Hydrogen
E. Chlorine
7. The ability of liquid oxygen to be attracted to a magnet is due to ______.
A. the unpaired protons in the nucleus
B. the charge on the oxygen atoms
C. the unpaired electrons
D. the charge on the magnet
E. the blue color
8. For the singly bonded Lewis dot structure for BF3. Which of the following statements best describes this structure?
A. It obeys the octet rule on all atoms.
B. It has less than an octet on at least one atom.
C. It has a lone pair of electrons on the boron atom.
D. It has less than an octet of electrons on all atoms.
E. It exceeds the octet rule.
9. For the singly bonded Lewis dot structure for SF6, Which of the following statements best describes this structure?
A. It obeys the octet rule on all atoms.
B. It has less than an octet on at least one atom.
C. It has a lone pair of electrons on the sulfur atom.
D. It has less than an octet of electrons on all atoms.
E. It exceeds the octet rule.
10. What is the hybridization of the carbon atoms in ethyne, C2H2?
A. sp D. sp3d
B. sp2 E. sp3d2
C. sp3
II. Answer the following questions. Support your answer with: (a) the appropriate Lewis Structure; (b) necessary computations in writing the Lewis Structure; or (c) computations in determining Formula Charge. (150 points)
1. How many bonds are expected in nitrogen dioxide molecule? (5 points)
2. How many bonds are available for bonding in phosphate ion, PO43-? (5 points)
3. Which of the following molecules or ions has the same electronic structure as N2?
A. O2 B. CN- C. CO
(15 points)
4. How many different molecules have the formula C5H12? (15 points)
4. How many possible resonance structures exist for sulfur trioxide? (15 points)
5. How many possible resonance structures exist for the formate ion, HCO2-? (10 points)
6. Which of the following species has a Lewis structure with a molecular geometry similar to CS2? (10 points)
A. H2S D. H2O
B. NO2- E. SCN-
C. NO2
7. Which of the following species has a Lewis structure with a molecular geometry similar to SF4? (10 points)
A. BrF4+ D. SO42-
B. ICl4- E. CCl4
C. NH4+
8. Which of the following species has a Lewis structure with a molecular geometry similar to NH3? (10 points)
A. CO32- D. ICl3
B. BH3 E. SO3
C. H3O+
9. Which of the following species has a Lewis structure with a molecular geometry similar to SO3? (10 points)
A. NH3 D. SO32-
B. ICl3 E. PCl3
10. How many lone pairs of electrons are on the sulfur atom in sulfite ion, SO32-? (5 points)
11. What is the formal charge on each atom in dichloromethane, CH2Cl2? (10 points)
12. What is the formal charge on each atom in CN-? (10 points)
13. Which of the following species have the same molecular geometry: H3O+, H2CO, NH3, and ICl3? (20 points)
III. Answer the following questions: (5 pts each)
A. Use VSEPR theory to predict the molecular geometry of:
1. SO32-
2. ICl3
3. Cl2CO
4. IF5.
B. What are the bond angles in:
1. CO32-?
2. phosphate ion?
3. SF4?
C. What is the hybridization of the carbon atoms in ethyne, C2H2?
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