Results of a Second Study of Students’
Utilization of Molecular Modeling in General
Chemistry: Comparison with Students Who
Did Not Utilize Molecular Modeling
Julie B. Ealy
ACS National Meeting
New York City - September 11, 2003
Penn State University
Berks-Lehigh Valley College
The Students
• All students were enrolled in first semester
chemistry
• Some students enrolled in lab as well as
lecture – hereafter referred to as the
treatment group
• Some students only enrolled in lecture –
hereafter referred to as the control group
• All students do not have to take lab
• Some students will take lab at a later time
2
The Procedure
• Content covered in lecture for treatment and
control groups
• Treatment group – 6 hours of lab utilizing
Spartan Pro
• Treatment group – administered long and
short response test in lab
• Previous students’ (AP Chemistry) incorrect
responses on a lab test utilized as multiple
choice responses on pre- and posttest and
semester exam
3
Molecular Modeling Lab Content
Treatment Group
Ealy
H2, HF, F2: Lewis dot, bond length, electrostatic
potential surface, dipole
CH4, CH3Br: bond length, bond angle
CH4, NH3, H2O: Lewis dot, bond angle, orbital
notation
HF, HCl, HBr, HI: bond length, electrostatic
potential surface, dipole
Organic molecules: identify by functional group,
hybridization
4
Molecular Modeling Lab Content
Treatment Group
Moog & Farrell
Bond order and bond strength
Bond length and bond strength
Resonance: benzene
Bond order and bond energy
Intermolecular forces: alkane, alcohol, ketone
5
Lecture Content Using Spartan Pro
Treatment and Control Groups
•
•
•
•
•
•
C2H6, C2H4, C2H2, C6H6
Models: ball and spoke, ball and wire, and
electrostatic potential surface
Bond length measurements - C-C bond
Dipole measurements
Bond length and energy discussed
Symmetry of the surfaces as related to the dipole
measurement
Resonance - C6H6.
6
Lecture Content Using Spartan Pro
Treatment and Control Groups
•
•
•
•
CH4 and CH3Br
Models - ball and spoke and electrostatic potential
surface
Bond length measurements C - H and C - Br
combined with electron density of Br and H
Dipole measurements and comparison of the
electrostatic potential surfaces
Electron density - Br lone pairs/red area on the
electrostatic potential surface of Br; blue area
around each H
7
Lecture Content Using Spartan Pro
Treatment and Control Groups
NH3, H2O, F2, SF6, and PF5
• Models - ball and spoke and electrostatic
potential surface
• Dipole measurements for NH3, H2O, and F2.
• Use of sp3d2 and sp3d orbitals for SF6, and
PF5, respectively was discussed.
8
Pretest/Posttest Questions and Semester Exam
Questions
• Pretest/posttest – 7 multiple choice
questions – all questions utilized images
provided to students – 5 sheets with 8-10
images from Spartan Pro per sheet
• Semester exam questions
– Spring 2002- 7 multiple choice questions
– Fall 2002 – 5 multiple choice questions
– no images were utilized
- 3 questions in common between the semesters
9
1. On Structure 6 the bond length between the central atom (carbon –
black) and the atom at the top (hydrogen – white) is shorter than the bond
length in a similar position on Structure 5 (bromine – red). The difference
can best be explained by the following
A.The Br atom elongates the bond because of its bonding pair – bonding
pair repulsion.
B. Lone pairs of electrons exhibit repulsion against other bonding pairs to
cause the bond to lengthen.
C. A higher bond energy between carbon and bromine contributes to a
longer bond length.
D. Bromine has more energy levels than hydrogen and its additional
electron density causes a longer C-Br bond length.
10
3. Structures 25, 26, and 27 are all linear molecules. They represent the
following molecules: BeCl2, HgBr2, and XeF2, respectively. An acceptable
explanation that explains that Structure 27 is XeF2 is
A. XeF2 would have the shortest bond length because F2 wants very much
to have an octet of electrons around it.
B. Xe is medium sized with lots of electrons and because of its low
electronegativity its pull on electrons are not that great.
C. The number of energy levels in Xe causes it to be the largest central
atom and the small size of the fluorine atom enables it to approach closer
to a central atom than Cl or Br could approach.
D. Xe has a high number of protons and would repel its many electrons
very far away which would create a large electron density around it
causing much repulsion with the fluorine atoms.
11
Semester Exam Example Question
All of the following pairs of molecular geometries
are correctly matched EXCEPT
Compound
Molecular Geometry
a) HBr
linear
b) CBr4
tetrahedral
c) AsH3
pyramidal
d) BeBr2
angular
e) CH4
tetrahedral
12
Semester Exam Example Question
Consider the following: Molecule
Bond Energy
Chlorine
243
Carbon dioxide
804
Nitrogen
945
The best explanation for the difference in bond energy is the
difference in the
a) polarity of the molecules
b) type of bonds in the molecules
c) electronegativity of the atoms that make up each
molecule
d) intermolecular forces between molecules
13
First Study – Spring 2002
Number of students = 23
Control
Pretest

1.50
sd
1.09
n
12
Treatment
 1.55
sd 0.820
n
11
Posttest
1.92
1.24
12
3.55
1.29
11
14
First Study – Spring 2002
Treatment vs. Control - Pretest
t test
0.112
p
.456
Posttest vs. Pretest – Control
t test
0.875
p
.195
Posttest vs. Pretest – Treatment
t test
4.33
p
.000162*
Treatment vs. Control – Posttest
t test
3.08
p
.0028*
15
First Study – Spring 2002
Semester Exam- 7 questions
Control

2.92
sd
1.38
n
12
Treatment vs. Control
t test
1.83
p
.0410*
Treatment
4.09
1.70
11
16
Second Study – Fall 2002
Number of students = 33
Control
Pretest

1.25
sd
0.707
n
8
Treatment
 1.68
sd 0.900
n
25
Posttest
1.63
0.744
8
2.88
1.364
25
17
Second Study – Fall 2002
Treatment vs. Control - Pretest
t test
1.23
p
.114
Posttest vs. Pretest – Control
t test
1.03
p
.160
Posttest vs. Pretest – Treatment
t test
3.67
p
.000302*
Treatment vs. Control – Posttest
t test
2.47
p
.0096*
18
Second Study – Fall 2002
Semester Exam – 5 questions
Control

2.38
sd
1.41
n
8
Treatment vs. Control
t test
2.02
p
.0258*
Treatment
3.44
1.26
25
19
Conclusions
• Utilization of molecular modeling does
make a difference in students’
understanding of questions pertaining to
molecular concepts either with or without
the presence of molecular images
• Multiple choice questions can be developed
from students’ incorrect responses
• A second study provided additional
verification of the importance of utilizing
molecular modeling
20
Conclusions
• It seems logical that utilization of molecular
modeling would increase students’ understanding
of molecular concepts. It’s good to know that this
can be tested and the results are statistically
significant as verified by the two studies.
• Students’ understanding of molecular concepts
who did not utilize molecular modeling did not
show a statistically significant gain on the
questions utilized in the two studies even though
the students were exposed to measurements and
manipulations of computer-generated models in
lecture.
21
Recommendations
• Instead of administration of a pretest/posttest to
another group of students, analyze the results of
the lab test of the treatment group to determine
students’ general misunderstandings of molecular
concepts.
• Interview students after completion of the unit on
molecular structure and concepts to further
determine their understanding or lack of
understanding of molecular concepts and
structure.
22