SOME TOUGH COLLEGE PROBLEMS!
LEWIS DOT STRUCTURES
1.
An acceptable Lewis dot structure for N2O is:
(A) O
:..
N
:..O
N
(D)
..:
..N
:
:..
..
..N ..N:
.. ..
:..
N
(B) O
O
(E) O
(C)
:..O
N
:
N
:
N
2.
Which molecule contains one unshared pair of valence electrons around the central atom?
(A)
H2O
3.
The most reasonable Lewis structure for NOCl is:
..
(A) : O
..
..
(D) : O
..
(B)
..N
NH3
(C)
CH4
..
Cl:
..
..
(B) : O
..
..N
..
Cl:
..
(E) N
:..
O
..
..N
(D)
NaCl
..
:
(C) O
..
Cl:
..
..
Cl:
..
..
N
..
Cl:
..
4.
How many electrons should be shown in the Lewis dot structure for carbon monoxide (CO)?
(A)
8
5.
The Lewis structure of NO2+ is best drawn as:
(A)
(D)
:....O
:....O
(B)
14
..N ..O : +
.. ..
..N O : +
..
(C)

10
..
(B) : O
..
..O
..
:..N
O
(E)
(D)
..N : +
..
..O +
:
28
(C)
..
:O
N
..O
+
:
6.
Which has a Lewis dot structure with the greatest number of unshared pairs on the central atom?
(A)
NH3
7.
Which molecule contains only two unshared pairs of electrons?
(A)
H2O
(B)
(B)
IF3
NH3
(C)
(C)
SeCl2
BeCl2
1
(D)
(D)
ICl2-
MgO
8.
Which of the following molecules would have a trigonal planar molecular arrangement?
(A)
CBr4
9.
In the Lewis structure of SF2, there are ____ single bonds and ____ total unshared pairs?
(A)
2,8
10.
Which of the following species is INCORRECTLY matched with the number of unshared pairs found
on the central atom?
(A)
SO42- 0
11.
Which of the following molecules violates the octet rule?
(A)
CBr4
12.
Which of these contains at least one multiple bond?
(A)
NO3-1 (B)
13.
Sulfur dioxide can be described by the structures below. This implies that:
(B)
(B)
(B)
(B)
PH3
..O
..
(A)
BF3
(C)
3,8
(C)
NO3- 1
NF3
(C)
..S
(C)
(C)
N2H4 (D)
OF2
2,2
(D)
(D)
XeF2 3
OF2
(D)
SiCl4 (E)
..O
..:
PCl3
2,6
(E)
(E)
AsF5
3,6
(D)
SO2
1
PCl3
(E)
AsF5
IF4-
(E)
2
BH4-1
..
:..O
..S
..O
..
(C)
(D)
The two bonds in SO2 are of equal length, and the electronic distribution in the two SO bonds is
identical, because the two different bonds seem to exchange positions.
The single bond is longer than the double bond and the electronic distribution in the two SO bonds is
different.
This molecule doesn’t exist in any form, due to the fact that the formal charges are constantly changing.
The SO2 molecule revolves so that the two different bonds seem to exchange positions.
14.
How many different resonance forms are possible for the oxalate anion, C2O4-2?
(B)
O
(A)
3
(B)
15.
Which molecule exhibits resonance?
(A)
O3
16.
What are the formal charges on the boron and nitrogen in the compound BF3-NH3?
(A)
-2 and +2
(B)
7
(C)
BeCl2 (C)
(B)
6
CO2
+2 and –2
(D)
1
(D)
H2Se (E)
(C)
(E)
0 and 0
2
O
O
C
C
O
4
NF3
(D)
F
+1 and –1
(E)
F
H
B
N
F
H
H
-1 and +1
17.
The structure of the CO32 – ion can be described by these Lewis structures which means that:
2-
..
:O:
..
:..O
2-
..
:O:
:O:
C
C
..
:..O
..:
O
2-
C
..
..O:
:..O
..
..O:
(A)
(B)
(C)
(D)
two CO bonds are single bonds, the third CO bond is a double bond.
these three independent forms of the CO32 – ion co-exist in nature.
CO3-2 doesn’t exist in nature at all.
the CO32 – ion exists in only one form which is a composite or average of the three structures shown
above, because the double bond is rapidly moving among the three forms.
18.
Which is the least significant contributing structure to the resonance hybrid of the nitrate ion?
(A)
-
..
: O:
..
:..O
(C)
: O:
N
..
..O:
-
(D)
..
..O:
:..O
N
..
:..O
..
: O:
N
19.
-
(B)
..
..O:
-
..
: O:
N
..O
:..
..O:
What are the formal charges on each of the atoms in the PH4+ ion?
(A) P = 0; H = ¼+
(B) P = 0, H = 0
(C) P = 4+; H = 1-
(D) P=1+; H=0
(E)P=0; H=1+
20.
What is the formal charge on the sulfur atom in the sulfate anion (SO4-2), drawn without an expanded
octet?
(A)
-2
(B)
0
(C)
+2
(D)
3
+4
(E)
+6
21.
What is the formal charge on the nitrogen atom in the nitrate (NO3-1) anion?
(A)
-2
(B)
-1
(C)
0
(D)
+1
(E)
+2
ENERGY IN VS. ENERGY OUT
22.
Given the bond energies (in kJ/mol) below, calculate the energy change (in kJ) for
C(g) + H2 (g) + F2 (g) CH2F2(g). Is this a spontaneous process – meaning, is it going to occur easily
without much effort?
C—H 414
C—F 486
(A)
+900
(B)
23.
Calculate energy change for NH3(g) + Cl2(g)NH2Cl(g) + HCl(g)using the bond energies:
–900
N—H 389 Cl—Cl 240 H—Cl 431
occur easily without much effort?
(A)
–337 kJ
(B)
H—H 435
(C)
F—F 159
–465
(D)
–1206
N—Cl 201. Is this a spontaneous process – meaning, is it going to
+337 kJ
(C)
–84 kJ
(D)
-3 kJ
24.
Calculate the energy change for the reaction, C2H4 + H2O  C2H5OH using the following bond energies
(in kJ/mol). Is this a spontaneous process – meaning, is it going to occur easily without much effort?
C-H
413
C-O
358
(A)
-37
(B)
+179
C-C
347
O-H
(C)
-441
467
H-H
432
C=C
614
(D)
-304
(E)
+2098
C=O
799
25.
Using the bond energies given, estimate the energy change for making carbonic acid (H2CO3) from CO2
and H2O. Is this a spontaneous process – meaning, is it going to occur easily without much effort?
C-O
(A)
+493 kJ/mol (B)
358
-493 kJ/mol
C-C
347
O-H
467
C=O
799
(C)
+83 kJ/mol
(D)
+799 kJ/mol (E)
(D)
Al
-467 kJ/mol
ELECTRONEGATIVITY AND BOND POLARITY
26.
Which would be expected to be the most electronegative?
(A)
P
27.
The element with the greatest tendency to gain electron(s) is:
(A)
F
28.
Which atom has the highest electronegativity?
(A)
Br
(B)
(B)
(B)
As
At
Mg
(C)
(C)
(C)
Si
O
C
4
(D)
N
(D)
O
(E)
Bi
29.
Which of these elements should be the most active as a nonmetal, given that their electronegativity
values are:
Q
0.9
(A)
Q
30.
Which of the following statements about electronegativity (EN) is FALSE?
(A)
(B)
(C)
(D)
Nonmetals usually have higher EN than metals
Differences in electronegativity greater than 1.7 tell us that the bond is non-polar covalent
HCl has a higher partial charge than HI because the EN of Cl > EN of I
In general, an atom’s EN is inversely related to its radius
31.
In which bond are the partial charges on the atoms correct?
(A)
+Si-O-
32.
Which of the following bonds are the MOST non-polar?
R
1.0
(B)
(B)
T
R
2.8
(C)
+Cl-Br-
T
3.0
(D)
+N-B-
(B)
As-Cl
33.
Which set of bonds is arranged in order of increasing polarity?
(A)
(C)
Si-S < Si-O < Si-P < Si-F
Si-F < Si-S < Si-O < Si-P
34.
The IF molecule may be represented by the formula I-F. The polarity is best represented as:
(A)
I
 
-F
Si-H
+Cl-Cl-
P-H
I
(C)
Z
(A)
(B)
Si
1.8
(E)
S
2.5
-F
Cl
3.0
X
4.0
H
2.1
(B)
(D)
As
2.1
(D)
Z
Atoms
Electronegativity
 
P
2.1
(C)
X
Sb
1.9
(D)
Sb-Cl
(E)
H-S
Si-O < Si-F < Si-S < Si-P
Si-P < Si-S < Si-O < Si-F
(C)
 
I
-F
(D)
 
I
-F
IONIC BONDING
35.
The lattice energy for ionic crystals increases as the charge on the ions ___ and the size of the ions ___.
(A)
(C)
increases, increases
decreases, increases
36.
Select the compound with the highest (most negative) lattice energy?
(A)
CaS
37.
Select the compound with the lowest (least negative) lattice energy?
(A)
CsBr (B)
(B)
(B)
(D)
MgO (C)
NaCl (C)
increases, decreases
decreases, decreases
NaI
SrO
(D)
(D)
LiBr
CaO
5
38.
Calculate the lattice energy for LiBr(s) given the following information:
Li(s)  Li(g), H = +166 kJ/mol
EA of Br(g) = -325 kJ/mol
Hf (LiBr) = -351 kJ/mol
IE of Li(g) = +520. kJ/mol
Br2(l)  2 Br(g), H = +194 kJ/mol
(A)
-906
-1479 (D)
-351
39.
Use a Born-Haber cycle based on the formation of MgO to determine heat released for the process, O(g)
+ 2e  O-2(g) in kJ/mol (The total electron affinity)
(B)
-1575 (C)
-809
(E)
Mg(s)  Mg(g) H = +150 kJ/mol
Hf (MgO) = -602 kJ/mol
Lattice energy of MgO(s) = -3920 kJ/mol
IE1 + IE2 Mg = +2180 kJ/mol
Bond energy of O=O = 498 kJ/mol
(A)
-1314
(C)
40.
Calculate the lattice energy of magnesium sulfide (MgS) given that (in kJ/mol):
Mg(s)  Mg(g)
S (s)  S(g)
(B)
+739
+137
H = +153
IE(1) Mg, IE(2) Mg
H = +557.5 EA(1) S, EA(2) S
(B)
+1786
H = +700, +1480
H = -100, -203
Hf (MgS)
-6833 kJ/mol
41.
Calculate the electron affinity of chlorine from the following data (in kJ/mol):
H = 85.8
H = -695
(A)
(B)
-530 kJ/mol
(C)
(E)
(A)
Rb(s)  Rb(g)
H(latt)(RbCl)
-2930.5 kJ/mol
(D)
H = 397.5
H = -431
IE (Rb)
Hf (RbCl)
-445 kJ/mol
(C)
2244 kJ/mol
-417 kJ/mol
(D)
(D)
diss E. (Cl2)
-141
H = -343
6147 kJ/mol
H =226
-332 kJ/mol
VSEPR
42.
Which pairs have the same molecular geometry?
(A)
SO2 and CO2
43.
The molecular geometry for SeF3+1 is:
(A)
trigonal pyramidal.
44.
The molecular geometry of BrF5 is:
(A)
square pyramidal.
45.
Which has a planar molecular geometry?
(A)
NH3
(B)
(B)
(B)
(B)
SO3-2
CO2 and OF2
(C)
square planar. (C)
trigonal pyramidal.
(C) CO3-2
PH3 and BF3
tetrahedral.
(C)
(D)
SO2 and O3
rectangular planar.
trigonal bipyramidal. (D)
(D) H3O+1
6
(D)
octahedral.
46.
Which molecule has a linear molecular geometry?
(A)
H2O
47.
A molecule consists of four bonding pairs of electrons and no lone pairs. What is its molecular
geometry?
(A)
square planar
48.
Which statement is true of methane?
(A)
(C)
It is a tetrahedral molecule.
It has extremely strong chemical bonds
49.
Which of the following molecules does NOT possess a trigonal pyramidal molecular geometry?
(A)
NH3
50.
Which of these molecules or ions has a square planar molecular geometry?
(A)
SiBr4
51.
Which compound would be expected to have charge, or molecular polarity?
(A)
SiO2
52.
Which molecule has a permanent molecular polarity or charge?
(A)
BCl3
53.
The bond type and molecular polarity of SiCl4 are:
(A)
(C)
(B)
(B)
NH3
(B)
COCl2
(B)
(B)
(B)
Bond Type
polar
nonpolar
(C)
tetrahedral
(C)
NH4+1
BCl3
CO2
NO2
(C)
(B)
(D)
H3O+1
(C)
(C)
(C)
(D)
linear
(E)
(D)
H2S
square pyramidal
It contains single and double bonds.
It does not occur in nature.
(D)
ClO4-
ClO3-1
(D)
SO2
(D)
CF4
Polarity of Molecule
nonpolar
polar
CO2
(D)
(B)
(D)
(E)
PF3
XeF4
CF4
H2O
Bond Type
polar
nonpolar
Polarity of Molecule
polar
nonpolar
54.
Which molecule is nonpolar?
(A)
CCl4
55.
Experiment shows that the molecule H2Se has a permanent dipole moment, or molecular polarity that is
not zero. Which statement MUST therefore be incorrect?
(A)
(B)
(C)
(D)
The H2Se molecule is linear.
The H2Se molecule is covalent.
The H2Se molecule is electrically neutral, or has no charge
There must be a difference in electronegativity between hydrogen and selenium.
(B)
HCl
(C)
CF3Cl
7
(D)
CHCl3
(E)
NH3
56.
Which of the following possesses polar bonds but has no molecular polarity or charge?
(A)
BF3
57.
Of the molecules CO2, NH3, H2O and CH4, which are polar?
(A)
(B)
CO2, NH3 and H2O
CO2 and NH3
58.
Which of the following has charge, or molecular polarity that is not zero?
(A)
BBr3
59.
Which of the following has no molecular polarity or charge?
(A)
CS2
(B)
O2
(B)
(B)
(C)
(B)
(E)
SF2
H2O
CHCl3
(D)
NH3, H2O and CH4
NH3 and H2O
(C)
(C)
XeF4
CH2F2
PF3
(C)
(E)
Cl2
CO2 and CH4
(D) CO2
(D)
PCl3
(E)
N2O
(E)
CH2O
GENERAL STUFF
60.
Which one of the following properties is NOT characteristic of substances composed of small,
covalently-bonded molecules, with no slight charge?
(A)
(D)
don’t dissolve in water
2 or more non-metals sharing electrons
61.
Which of the following properties is least characteristic of metals?
(A)
(D)
high melting point
(B)
good electrical conductor when solid (E)
62.
Which of the following properties is least characteristic of ionic compounds?
(A)
(D)
high melting point
usually solids
(B)
(E)
(B)
(E)
low boiling point
usually gases
high boiling point
shiny and lustrous
(C)
(C)
usually solids
brittleness
high boiling point
(C)
transfer of electrons
poor electrical conductor when molten
8