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

2 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

3 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

4 Molecular Modeling Lab Content Treatment Group Ealy H 2, HF, F 2 : Lewis dot, bond length, electrostatic potential surface, dipole CH 4, CH 3 Br: bond length, bond angle CH 4, NH 3, H 2 O: Lewis dot, bond angle, orbital notation HF, HCl, HBr, HI: bond length, electrostatic potential surface, dipole Organic molecules: identify by functional group, hybridization

5 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

6 Lecture Content Using Spartan Pro Treatment and Control Groups C 2 H 6, C 2 H 4, C 2 H 2, C 6 H 6 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 - C 6 H 6.

7 Lecture Content Using Spartan Pro Treatment and Control Groups CH 4 and CH 3 Br 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

8 Lecture Content Using Spartan Pro Treatment and Control Groups NH 3, H 2 O, F 2, SF 6, and PF 5 Models - ball and spoke and electrostatic potential surface Dipole measurements for NH 3, H 2 O, and F 2. Use of sp 3 d 2 and sp 3 d orbitals for SF 6, and PF 5, respectively was discussed.

9 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 multiple choice questions –Fall 2002 – 5 multiple choice questions – no images were utilized - 3 questions in common between the semesters

10 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.

11 3. Structures 25, 26, and 27 are all linear molecules. They represent the following molecules: BeCl 2, HgBr 2, and XeF 2, respectively. An acceptable explanation that explains that Structure 27 is XeF 2 is A. XeF 2 would have the shortest bond length because F 2 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.

12 Semester Exam Example Question All of the following pairs of molecular geometries are correctly matched EXCEPT CompoundMolecular Geometry a)HBrlinear b)CBr 4 tetrahedral c)AsH 3 pyramidal d)BeBr 2 angular e)CH 4 tetrahedral

13 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

14 First Study – Spring 2002 Number of students = 23 Control PretestPosttest þ sd n1212 Treatment þ sd n 1111

15 First Study – Spring 2002 Treatment vs. Control - Pretest t test p.456 Posttest vs. Pretest – Control t test p.195 Posttest vs. Pretest – Treatment t test 4.33 p * Treatment vs. Control – Posttest t test 3.08 p.0028*

16 First Study – Spring 2002 Semester Exam- 7 questions ControlTreatment ü sd n1211 Treatment vs. Control t test 1.83 p.0410*

17 Second Study – Fall 2002 Number of students = 33 Control PretestPosttest þ sd n88 Treatment þ sd n 2525

18 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 * Treatment vs. Control – Posttest t test 2.47 p.0096*

19 Second Study – Fall 2002 Semester Exam – 5 questions ControlTreatment ü sd n825 Treatment vs. Control t test 2.02 p.0258*

20 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

21 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.

22 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.