Exam #4 Sample Test
Sample Exams are designed to give you an idea of the types of questions you can expect. Questions may not exactly agree with currently assigned material, so you may need to examine other sample exams. Answers for Sample Exam #4 are available.
1. FILL-IN-THE-BLANK each of the following questions.
In general the ionization energy and electron affinity increase from ______________________ (left to right or right to left) in a period of the periodic table.
Which of the following elements -- Be, B, C, & N -- has the smallest ionization energy? ___________________
Which of these elements -- Li, O, Ne, & Na -- has the largest atomic radius? _______________
________________________ describes the energy required to remove an electron from a gaseous atom or ion?
________________________ is the energy change associated with the addition of an electron to a gaseous atom.
The ____________________________ is the change in energy that takes place when separated gaseous ions are packed together to form an ionic solid.
_____________________________ is the term used to describe the mixing of native atomic orbitals to form special orbitals for bonding.
Which has the larger atomic radius, P or Sb? _________________________
Which has the larger ionic radius, O2- or F- ? _________________________
2. Answer the following TRUE/FALSE questions.
___T ___F Valence electrons are found on the outermost principal quantum level of an atom.
___T ___F When a metal reacts with a nonmetal a covalent bond is formed.
___T ___F A nonpolar covalent bond results from the unequal sharing of a pair of electrons between atoms in a molecule.
___T ___F A double bond occurs when two atoms share two pairs of electrons.
___T ___F The shape of an ammonia molecule is tetrahedral.
___T ___F The Lewis structure for CHCl3 has 9 lone electron pairs.
___T ___F The shape of a carbon dioxide molecule is linear.
___T ___F The size in a series of isoelectronic ions increases as the nuclear charge increases
___T ___F Whenever a set of equivalent tetrahedral atomic orbitals is required it will adopt a set of sp3 orbitals.
___T ___F The hybridization of the B in BH3 is sp3
___T ___F In the Lewis structure for SF4 the central sulfur atom shares 12 electrons.
___T ___F Since double bonds have two pairs of electrons, double bonds are longer than single bonds because of electron repulsion.
3. Draw Lewis dot structures for each of the following compounds or ions. Then, give its molecular geometry (if it has a structure we have not studied, write "none") Formulas for molecules and ions are correct
PF6-
NI3
PCl4+
ClO2
XeF6
SiH4
H3PO4
BF3
4. Using the bond energies shown, estimate the heat of combustion for one mole of acetylene:
C2H2 (g) + (5/2)O2 (g) --> 2CO2 (g) + H2O(g)
Bond Bond Energy (kJ/mol)
C=C (triple bond) 839
C-H 413
O=O 495
C=O 799
O-H 467
5. Given the following information, calculate the bond energy of a single N-F bond.
N2 bond energy = 941 kJ/mol
F2 bond energy = 154 kJ/mol
1/2 N2 (g) + 3/2 F2 (g) --> NF3 (g) DHo = -103 kJ/mol
6. Draw the Lewis structures for each of the molecules listed below. Then, answer the following questions (more than one answer may be correct):
BH3
O3
NO2
PCl5
SF6
_____________________________________ Which molecule(s) obey the octet rule?
_____________________________________ Which molecules have no dipole moment?
_____________________________________ Which of these molecules show resonance?
7. Given the following information (equations can be reversed, if necessary):
Li (s) --> Li (g) heat of sublimation of Li(s) = 166 kJ/mol
Li (s) --> Li (g) heat of sublimation of Li(s) = 166 kJ/mol
HCl (g) --> H (g) + Cl (g) bond energy of HCl = 427 kJ/mol
Li (g) --> Li+ (g) + e- ionization energy of Li
(g) = 520. kJ/mol
Cl (g) + e- --> Cl- (g) electron affinity of Cl (g) = -349
kJ/mol
Li+ (g) + Cl- (g) --> LiCl(s) lattice energy of
LiCl(s) = -829 kJ/mol
H2 (g) --> 2H (g) bond energy of H2 = 432 kJ/mol
Calculate the net change in energy for the reaction: 2Li (s) + 2HCl (g) --> 2LiCl (s) + H2 (g)
8. Draw all possible resonance structures for each of the following two ions (atoms must be in the order shown):
NCO-
CNO-
9. Consider the structure of glycine (draw complete Lewis structure), the simplest amino acid:
NH2-CH2-COOH
a. What is the orbital hybridization for each of the N, C, and O atoms in glycine?
b. What is the total number of bonds in the molecule?
c. What is the total number of p bonds in the molecule?
These multiple choice questions are beneficial to study. Answers given at the end of this page.
1. Atoms having greatly differing electronegativities are expected to form:
a. no bonds
b. polar covalent bonds
c. nonpolar covalent bonds
d. ionic bonds
e. covalent bonds
2. Choose the compound with the most ionic bond.
a. LiCl
b. KF
c. NaCl
d. LiF
e. KCl
3. For the elements Rb, F, and O, the order of increasing electronegativity is:
a. Rb < F < O
b. Rb < O < F
c. O < F < Rb
d. F < Rb < O
e. None of these
4. Based on electronegativities, which of the following would you expect to be most ionic?
a. N2
b. CaF2
c. CO2
d. CH4
e. CF4
5. Which of the following elements has the highest electronegativity?
a. Ba
b. Ca
c. Si
d. P
e. Cl
6. Based on electronegativity differences, which of the following is most likely to be ionic?
a. BaF2
b. Cl2
c. NH3
d. NO3
e. CH4
7. How many of the following molecules possess dipole moments?
BH3, CH4, PCl5, H2O, HF, H2
a. 1
b. 2
c. 3
d. 4
e. 5
8. Which of the following molecules has no dipole moment?
a. CO2
b. NH3
c. H2O
d. all
e. none
9. Choose the statement that best describes the PbCl4 molecule in the gas phase.
a. The bond angles are all about 109o.
b. The molecule is polar.
c. The molecule has a dipole moment.
d. The bonds are nonpolar.
e. The bond angles are all about 109o, the molecule is polar, and
the molecule has a dipole moment.
10. Which of the following has the smallest radius?
a. Cl-
b. K+
c. Cr
d. Al3+
e. Ar
11. Which of the following has the smallest ionic radius?
a. Ca2+
b. Cl-
c. Li+
d. O2-
e. Be2+
12. Which of the following ionic compounds has the largest lattice energy, i.e., the lattice energy most favorable to a stable lattice?
a. CsI
b. LiI
c. LiF
d. CsF
e. MgO
13. Calculate the lattice energy for LiF(s) given the following:
sublimation energy for Li(s) +161 kJ/mol
delta Hf for F(g) +77 kJ/mol
first ionization energy of Li(g) +520. kJ/mol
electron affinity of F(g) -328 kJ/mol
enthalpy of formation of LiF(s) -617 kJ/mol
a. 285 kJ/mol
b. -650. kJ/mol
c. 800. kJ/mol
d. -1047 kJ/mol
e. None of these
14. When electrons in a molecule are not found between a pair of atoms but move throughout the molecule, this is called
a. ionic bonding.
b. covalent bonding.
c. polar covalent bonding.
d. delocalization of the electrons.
e. a dipole moment.
15. As the number of bonds between two carbon atoms increases, which one of the following decreases?
a. number of electrons between the carbon atoms
b. bond energy
c. bond length
d. all of these
e. none of these
16. How many of the following molecules or ions contain double or triple bonds?
NH3 NH4+ HCN CO2 NO2
a. 0
b. 1
c. 2
d. 3
e. 4
17. How many of the following molecules -- SF2, SF4, SF6, SiO2 -- are polar?
a. 0
b. 1
c. 2
d. 3
e. 4
18. Which of the following molecules are nonlinear?
NO2-, C2H2, N3-, HCN, CO2, H2O2
a. C2H2, HCN
b. CO2, N3-
c. NO2-, H2O2
d. N3-, NO2-
e. all are linear
19. In the molecule C2H4 the valence orbitals of the carbon atoms are assumed to be
a. not hybridized.
b. sp hybridized.
c. sp2 hybridized.
d. sp3 hybridized.
e. dsp hybridized.
20. Which of the following molecules contains an sp2-sp2Æ sigma bond?
a. CH4
b. C2H2
c. C2H4
d. C2H6
e. none of these
21. The hybridization of Br in BrF3 is
a. sp
b. sp2
c. sp3
d. dsp3
e. d2sp3
22. If four orbitals on one atom overlap four orbitals on a second atom, how many molecular orbitals will form?
a. 1
b. 4
c. 8
d. 16
e. none of these
TRUE/FALSE
23. In general, a larger atom has a smaller electronegativity.
24. The shape of a carbon dioxide molecule is linear.
25. When an electron pair is shared in the area centered on a line joining the atoms a sigma bond is formed.
SHORT ANSWER
26. When nonmetals chemically combine, they tend to form what type of bond?
FILL-IN-THE-BLANK
27. The __________ of a molecule shows how the valence electrons are arranged among the atoms in the molecule.
28. When several nonequivalent Lewis structures can be drawn for a molecule, __________ is used to determine the most appropriate structure(s).
ANSWER KEY FOR TEST
1. d
2. b
3. b
4. b
5. e
6. a
7. b
8. a
9. a
10. d
11. e
12. e
13. d
14. d
15. c
16. d
17. c
18. c
19. c
20. c
21. d
22. c
23. False
24. True
25. True
26. covalent
27. Lewis structure
28. formal charge