Using Computational Chemistry Activities To Promote Learning and

May 13, 2014 - Joseph W. Ochterski. East Hampton High School, East Hampton, Connecticut 06424 United States. J. Chem. Educ. , 2014, 91 (6), pp 817–8...
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Using Computational Chemistry Activities To Promote Learning and Retention in a Secondary School General Chemistry Setting Joseph W. Ochterski East Hampton High School, East Hampton, Connecticut 06424 United States S Supporting Information *

ABSTRACT: This article describes the results of using state-of-the-art, research-quality software as a learning tool in a general chemistry secondary school classroom setting. I present three activities designed to introduce fundamental chemical concepts regarding molecular shape and atomic orbitals to students with little background in chemistry, such as one might find in a secondary school or first-year college chemistry course for nonmajors. Pilot studies employing the Shapes of Molecules and Atomic Orbitals activities demonstrate that students learn and retain key concepts.

KEYWORDS: High School/Introductory Chemistry, First-Year Undergraduate/General, Laboratory Instruction, Physical Chemistry, Computer-Based Learning, Computational Chemistry, Molecular Modeling, Quantum Chemistry, Theoretical Chemistry

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INTRODUCTION Chemistry is a difficult subject for many students, both at the secondary school level and at the college level for nonchemistry majors. Students face the challenge of assembling a mental model of atomic scale conditions and relating it to macroscopic phenomena. One piece of developing this construct is being able to imagine atoms and molecules and how they interact. The advent of computers has allowed chemists to create programs that aid in visualizing how atoms are arranged and predicting how they affect each other. However, these tools, which are so useful in research and education at the upper levels, are seldom used to present concepts at the secondary level1 and in introductory chemistry courses for nonmajors at the college level.2 Much of what has been reported is focused on second-year and beyond college chemistry classes.3−7 Very few studies have been reported discussing the use of research-grade computational chemical software as a learning aid for students in introductory college level courses.8−11 Fewer still attempt to use these tools to introduce important chemical principles to students at the high school level or to nonscience majors. Still, some resources aimed at high school level are available.12−14 This endeavor differs from previous work at the high school level15 in that is it aimed at students’ first collegepreparatory or honors general chemistry course, rather than college level (AP) chemistry or specialized chemistry electives. In this article, I describe three activities specifically designed for students in high school and introductory level college courses for nonscience majors that use state-of-the-art research-quality computational chemistry, Gaussian 09,16 and visualization, GaussView,17 software. The Getting Started activity helps students become familiar with the software, while the other two address topics in general chemistry where visualizing and interacting with © XXXX American Chemical Society and Division of Chemical Education, Inc.

chemical models is especially useful: atomic orbitals and shapes of molecules. I present the results of two pilot studies completed with these activities, which are available as Supporting Information for this article.

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DESIGN CONSIDERATIONS

Collective Goals

I kept several collective goals in mind while developing each of the activities. First, the activity had to directly address common student misconceptions about the topic. To this end, I chose misconceptions described in the recently revised ChemSource SourceBook,18,19 as well as some from my own experience. These are listed in Table 1. Second, the text for the student-centered part of the activity had to be accessible to students with relatively little background in chemistry and who may still be developing literacy skills. I took care to avoid relying on knowledge of any but the most basic chemical terms and to define and explain new vocabulary. Below is a sample paragraph from the introduction to the Atomic Orbitals activity showing the style of writing. It took 12 years and the work of many chemists and physicists, but ultimately Erwin Schrödinger came up with the right combination of mathematical pieces to describe atoms in general. One of his key insights was that the electrons in atoms were located in orbitals rather than orbits. An orbit is the path one object takes when it goes around another object. If an electron was in an orbit, you would be able to tell where it is and where it is going next. Experiments show that you cannot do that in real life. Orbitals are a way to take care of that problem.

A

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Table 1. Learning Objectives and Misconceptions Addressed Activity Getting Started Atomic Orbitals

Shapes of Molecules

Learning Objectives

Misconceptions Addressed

background knowledge and skills for using the Gaussian and GaussView state the differences between an orbit and an orbital explain why the modern quantum model is better than the Bohr model explain why atoms have no hard edge or boundary describe the shape of s, p, and d orbitals using both verbal and nonverbal methods using mnemonic devices for remembering the shapes of orbitals state how the sizes of orbitals change both within and among energy levels show how orbitals on the same atom overlap each other in threedimensional space give the names and shapes of five basic molecular geometries be able to identify central and terminal atoms in chemical structures be able to construct models of simple molecular structures using GaussView run a calculation to optimize a geometry using Gaussian relate the geometric arrangement of lone pairs and bonds about a central atom to electron repulsions

all chemists work in laboratories electrons orbit the nucleus like the planets around the sun each orbital exists alone in space an orbital is the same as an orbit there is an edge or boundary to an atom air exists between the particles (protons, neutrons and electrons) in atoms

the number of electron pairs surrounding a central atom is equivalent to the molecular geometry of the resultant molecule

necessary. The Getting Started activity, teacher guide, and worksheet are provided in the Supporting Information. The Shapes of Molecules activity introduces students to the general terminology necessary for understanding why molecules have particular shapes and also to the five common molecular shapes: linear, bent, triangular planar, triangular pyramidal, and tetrahedral. Because these activities are designed for beginning levels, I chose to limit the shapes to those that students are most likely to see again in other science courses. The emphasis in this activity is to develop the skill of being able to predict an ideal three-dimensional geometry from a Lewis structure using the number of lone pairs and atoms bonded to a central atom. The activity does not address deviations from ideal geometries due to the nature of its intended audience. The first part of the activity presents vocabulary essential to the activity. In the second part, students are asked to draw Lewis structures and then build and measure several different molecules and identify their shapes using the software. A common misconception students have is “The number of electron pairs surrounding a central atom is equivalent to the molecular geometry of the resultant molecule.”19 In other words, students often take the short cut of simply counting the pairs of electrons, and using the result to assign the molecular geometry. For example, both CH4 and H2O have four pairs of electrons around the central atom, so a student may assign tetrahedral geometry to both molecules although water is a bent molecule. The module addresses this by having the students separately count the number of atoms and lone pairs attached to the central atom and then sum them. The students explicitly identify patterns in how bonding and lone pairs relate to different geometries. There are three sets of molecules included in the activity, which can be used on an individual basis to differentiate instruction. The first set has only neutral singly bonded structures that obey the octet rule and illustrate four of the five shapes. Triangular planar structures are omitted since there are no such structures that satisfy the other criteria for this set. The second set includes structures with multiple bonds and provides several examples of planar-triangular structures as well as a linear molecule with more than two atoms (CO2). The final set includes structures with multiple bonds, incomplete octets, and nonzero charges. Each set of molecules is presented on a separate page to simplify making combinations of the sets.

Another principle used in the design of the activities was to divide the activities into relatively short segments where the students alternate between reading to acquire knowledge and an exercise applying that knowledge. This helps the students stay engaged and also promotes learning.20 A fourth consideration was that each of the activities was designed to be used independently, although both activities assume at least some experience from the Getting Started activity. Therefore, once some or all of the Getting Started activity is completed, the other activities may be used in any order. Finally, each activity includes an instructor guide indicating what student background is expected, the major chemical concepts addressed, the objectives of the activity, typical results, and the time that the activity is expected to take. Although these activities use Gaussian 09 with GaussView for the graphical interface, the concepts underlying them could be adapted for use with other software, such as WebMO.21 Using sophisticated software engaged students more than they might have been with an animation or simpler simulation and gave them the impetus to work through the inevitable challenges that arose. See the section on the pilot programs below for more details. Individual Goals

In addition to the collective design goals, both of the activities were designed with individual goals. The Getting Started activity is broken into several parts to introduce students to the software. After a general introduction, there are sections explaining how to use GaussView to build, rotate, move, and measure molecules, and finally a section describing in a general sense what Gaussian can do and how to start calculations with GaussView. Each of these sections includes a stepwise procedure demonstrating the process involved. This activity also includes a worksheet with a parallel structure for the students to complete while they read through the activity. It focuses attention on various aspects of each section, sometimes asking students to restate the most important information and other times asking them to think a bit beyond what they have just read. The Getting Started activity need not be completed in its entirety prior to using the other activities. For example, the section on measuring molecules is not necessary for completing the Atomic Orbitals activity. The teachers’ section of each activity indicates which parts are B

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Table 2. Description of Assessment Questions for Shapes of Molecules Activity Question

Description

Knowledge or Skill Needed

1 2

special case of diatomic molecules role of ligands on the central atom

3 4 5 6 7 8 9 10 11 12

identify the shape of a bent molecule from an illustration identify the shape of a triangular planar molecule from an illustration identify the shape of a tetrahedral molecule from an illustration definition of a central atom definition of a terminal atom identify the molecular shape from chemical formula (tetrahedral) identify the unshared pair of electrons in a Lewis structure identify the molecular shape from a Lewis structure (triangular pyramidal) identify the molecular shape from a Lewis structure (tetrahedral) identify the molecular shape from a Lewis structure (bent)

diatomic molecules are linear molecular shape is determined by the number of lone pairs and atoms bonded to the central atom vocabulary vocabulary vocabulary vocabulary vocabulary drawing Lewis structures and determining the shape from the drawing vocabulary, interpreting Lewis structures identify shape from Lewis structures identify shape from Lewis structures identify shape from Lewis structures

common (Questions 1 through 7), formulated to address essential vocabulary and common misconceptions about molecular shapes. The longer term assessment was given to ascertain how well students retained what they had learned during the activity and had five additional questions (Questions 8 through 12) to test how well the students were able to apply what they had learned. Three of the questions asked students to find the shape of a molecule from a Lewis structure (Questions 10 through 12), one asked them to find the structure from a formula (Question 8), and the final one (Question 9) asked them to identify the location of an unshared pair of electrons. Finding the three-dimensional shape of a molecule from its formula requires combining two skills, first drawing a Lewis structure, then interpreting it in three dimensions. Since drawing a Lewis structure from a formula was a potential prerequisite for this activity rather than the focus, more emphasis was placed on finding the shape from a Lewis diagram. The questions used in the assessments are described in Table 2. The questions themselves are provided in the Supporting Information. The participants in this pilot were 11th and 12th grade students, 24 in an honors-type section of high school chemistry and 71 in three midlevel sections of college preparatory high school chemistry. Groups of three students worked on the activity for three 48 min sessions, the first two sessions were separated by a week, with the last session 2 days after the second. In each group, one student was selected to be the “driver”, the person who operates the computer and mouse. The software was used during the first two sessions, while the final session was reserved to allow students to discuss and work together on the analysis portion of the activity. Prior to beginning the Shapes of Molecules activity, the students had completed several parts of the Getting Started activity: building simple molecules, rotating and moving molecules, and measuring molecules. Students were very engaged while working with the software. Approximately 90% of the students in each section were consistently engaged during both sessions. Because Gaussian and GaussView are research-quality software, it is presumed that the users will have significant chemistry experience and, therefore, substantially developed chemical intuition when building molecules. Although these students had relatively little exposure to chemistry in the past and were still learning the patterns inherent in chemistry, they were able to use the software to good effect. Students were willing to try different ideas until they found the structures that matched their Lewis structures, rather than simply trying once and giving up. Perhaps this is because, with software, interrupting and starting over has little cost associated

Since students starting out in chemistry sometimes differ vastly in their ability to draw correct Lewis structures, the activity includes versions of the worksheets with the Lewis structures already filled in. These may be used at the instructor’s discretion to eliminate the requirement that students be able to create Lewis structures on their own. However, students will still need to be able to interpret them. In the data analysis section, students look for patterns among the three-dimensional shapes and Lewis structures to uncover the relationships between the two molecular representations. The Supporting Information contains the activity, a teacher’s guide, and worksheets for the Shapes of Molecules activity. There are four versions of the worksheets provided: one with all columns blank, one with only the Lewis structures filled in, one with Lewis structures and the number of atoms and lone pairs on a central atom filled in, and one with all the columns filled in except for the column containing a sketch of the molecules. The Atomic Orbitals activity explains the difference between orbits and orbitals and then looks at the structure of an orbital and its relationship to waves. Finally, the students look at a variety of atomic orbitals (s, p, d, and f) to discover the relationships between orbital size and energy level, orbital type and number of orbitals in a subshell, and orbital type and shape. Care is taken to limit the amount of vocabulary students need to know to understand the basic concepts. This activity has an accompanying worksheet for students to work on while they go through the activity, which includes short answer questions directly addressing the common student misconceptions listed in Table 1. The answers for these questions can be found in the accompanying text. Other questions ask students to sketch general shapes and sizes of orbitals, which helps students form nonlinguistic representations that aid in understanding.20 Using Gaussian for this part of the activity gives realistic sizes and shapes of orbitals. The Supporting Information provides the Atomic Orbitals activity, teacher’s guide, and worksheet.

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PILOT STUDIES The pilot studies were run using eight desktop personal computers in a high school library that functions as a computer lab. The computers had configurations typical of those found in many high schools today. Copies of these activities are available as Supporting Information for this article. Shapes of Molecules Activity

The first study consisted of a pretest, the Shapes of Molecules activity, an immediate post-test, and then a longer term post-test. The three assessments had seven multiple-choice questions in C

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to interpret, although the difference in outcome could be due to additional studying by students. The responses for the five application questions appear less successful than the first seven questions. For the upper level students, three questions stood out. For Questions 10 and 12, students needed to be able to ascertain the correct molecular shape from a given Lewis structure. For Question 8, they needed to be able to find the Lewis structure in addition to determining the shape. Students were successful identifying a tetrahedral shape for a Lewis structure in Question 11, which suggests that the difficulty in Question 8 was in deducing the Lewis structure. Middle-level students had even less success on Questions 10 and 12, and had difficulty on Question 11. These results show improvement over my previous classes when ball and spring molecular models were used, although there was no control group in this pilot study to confirm this. In previous classes, approximately 65% of upper-level students and 40% of midlevel students were able to identify the correct molecular shape when given a Lewis structure. Also in prior classes, roughly 75% of upper level students and 60% of midlevel students would be able to correctly answer questions similar to the seven used in all the assessments. The results intimate a narrowing of the gap in performance between upper-level and midlevel students. The results of this pilot study indicate that it was successful in helping students understand the vocabulary and ideas necessary for determining molecular shape. Further, the students’ understanding was stable over a three week time span. The somewhat less successful outcome on the application questions of the longer term post-test suggests that an additional session, where students practice using findings from this activity, would be beneficial.20

with it. There was quite a bit of discussion among group members as they collaborated to generate the structures. Even students who were generally reticent added to the discussions. For all class sections, the pretest was administered immediately prior to the first session of the activity. The immediate posttest was given 2 days after the final activity session, and the longer term post-test was administered approximately 3 weeks later. The results of the assessments are given in Table 3. Table 3. Percent of Students with Correct Answers on the Shapes of Molecules Activity Assessments Upper-level (N = 24)

Question

Pretest

Immediate Post-test

1 2 3 4 5 6 7 average 8 9 10 11 12 average

91.6 41.6 79.2 58.3 37.5 95.8 33.3 62.5

95.8 91.6 100 95.8 62.5 100 91.6 91.0

Longer Term Post-test 95.8 87.5 95.8 79.1 79.1 100 83.3 88.7 70.8 95.8 70.8 91.6 66.7 79.1

Middle-level (N = 71)

Pretest

Immediate Post-test

86.4 42.4 59.1 43.9 24.2 72.7 28.8 51.1

93.9 83.3 97.0 81.8 47.0 87.9 74.2 80.7

Longer Term Post-test 97.0 72.7 93.9 75.8 68.2 92.4 75.8 82.3 71.2 84.8 37.9 69.7 40.9 60.9

The averages are given separately for the first seven questions and the additional five questions from the longer term assessment. The five additional questions were devised after the immediate post-test, and so no data is available for those on the earlier assessments. For both the upper-level and middle-level class sections, the greatest gains were made between the initial and final assessments for Question 7, which relates to the definition of terminal atom. The smallest gains were made for Question 1, which deals with the special case of diatomic systems being linear and had very high results on the pretest. Question 5 had a surprising result in that there were substantial gains at both levels between the immediate and longer term posttests, although no additional practice or activity took place. This question asked students to identify a generic tetrahedral structure from an image. I noticed that both sets of students had the least success by a wide margin on this question on the intermediate assessment and suspected that this might be due to students having difficulty interpreting the diagram used for this question (Figure 1A), so I replaced it on the longer term post-test with a different drawing (Figure 1B). The improved performance on this question suggests that this diagram was easier for students

Atomic Orbitals Activity

The second pilot study also consisted of three parts: a pretest, the Atomic Orbitals activity, an immediate post-test, and then a final longer term post-test. All seven questions on both of the first two assessments were identical. On the final post-test, the questions were rewritten to focus on the application of the concepts, in order to minimize students simply repeating memorized answers from previous assessments. The questions were designed to directly address many of the learning objectives given in Table 1 as directly as possible and were all open-ended. Two of the learning objectives were not assessed during this pilot study. First, the objective concerning the improvements in the quantum mechanical model over the Bohr model was inadvertently omitted. Second, the objective about how orbitals overlap in three-dimensional space was omitted, since I was not able to formulate a question in such a way that students could understand what I was asking for, without also giving the answer as part of the question. A description of each question is given in Table 4. The questions can be found in the Supporting Information. In this second pilot study, the students were again in 11th and 12th grade. All 71 were enrolled in an honors type section of high school chemistry. Some students were not available for the pretest or the immediate post-test, so the total number of students involved is lower. Groups of three students worked cooperatively on the activity during two 48 min sessions, separated by 11 days. About 10 days before the Atomic Orbitals activity, the students had been in the computer lab to complete selected parts of the Getting Started activity: building simple molecules and rotating and moving molecules. The size of the classes and number of computers used dictated that one student

Figure 1. Depiction of tetrahedral molecules for Question 5 from the pretest and immediate post-test (A) and from the final longer term post-test (B). D

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Table 4. Description of Assessment Questions for Atomic Orbitals Activity Question

Description

1

difference between an orbit and an orbital explain why atoms have no hard edge or boundary draw s, p, and d orbitals how to remember the shapes of s, p, d and f orbitals size of orbitals within an energy level size of orbitals in different energy levels composition of an orbital

2 3 4 5 6 7

since the most common incorrect answer, which comprised about 75% of all incorrect answers, referred to the difference in size of orbitals in dif ferent energy levels. The version of the question used on the final assessment explicitly used orbitals from the same energy level (3s and 3p). Still, students seemed to misinterpret the question, since about 80% of the incorrect answers compared the number of electrons in the 3s subshell to the number of electrons in the 3p subshell. This suggests that students may be confusing orbitals with subshells, both of which have the same label (either 3s or 3p).

Knowledge or Skill Needed vocabulary orbitals only describe where an electron is likely to be found shapes of orbitals mnemonics for the shapes of orbitals orbitals in the same energy level are similar in size orbitals in the higher energy levels are generally larger in size orbitals are empty space

Overall Results

At the high school level, much of the chemistry-related material made available to students using computers is limited to animations and simulations. Young, inexperienced students sometimes view these activities as toys or games and treat them casually. Using research-quality software, as these activities do, gives students the sense that their learning is being taken seriously and encourages them to take it seriously as well. The results of these pilot studies support this notion, since they indicate that students were engaged, achieved most of the learning objectives, and retained that achievement for some time. Thus, using research-quality software can be an effective means of learning even for students with very little chemistry background. These activities are designed, in both content and literacy level, to meet the needs of beginning general chemistry students at the high school and introductory college level. The activities may also be used with students in upper-level chemistry courses by increasing the difficulty of the questions and variety of the molecules.22 Using research-grade software engages students, showing them that the instructor sets high expectations for learning and is confident that students can meet those standards.

in each group be selected to interact with the computer while the others watched and commented. On the day following the second computer session, I lead a 30 min review of the worksheets so students could check their answers and ask any additional questions they might have. I administered the immediate post-test 2 days later and the long-term post-test 2 weeks after that. Students were provided with the results of their immediate post-test prior to the long-term one, but no additional class time was used after the immediate assessment. During the Atomic Orbitals activity, students were highly engaged, as evidenced by these unsolicited quotes: “I like this program, it’s fun” and “I like to watch the atoms spin”, as well as many others. That enthusiasm seemed to translate to a high degree of learning as shown in Table 5. Students had very little Table 5. Percent of Students with Correct Answers on the Atomic Orbitals Activity Assessments Question

Pretest (N = 63)

Immediate Post-test (N = 69)

Final Post-test (N = 71)

1 2 3 4 5 6 7 average

0.0 11.1 0.0 0.0 0.0 12.7 0.0 3.3

76.8 69.6 92.7 95.7 49.2 87.0 82.6 79.1

90.1 87.3 100 94.3 59.1 81.7 91.5 86.3

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ASSOCIATED CONTENT

S Supporting Information *

Complete copies of the three activities, including student handouts, instructor guides, and typical answers to the activity questions; a complete copy of a fourth, unevaluated activity on periodic trends; all questions used in the assessments; scheme file for GaussView. The documents in the Supporting Information are reprinted with the permission of Gaussian, Inc. This material is available via the Internet at http://pubs.acs.org.

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knowledge of atomic orbitals prior to the activity, only what they recalled from a brief introduction two to three years prior in an integrated science class. As an immediate result of the activities, more than 80% of the students had achieved the majority of the learning objectives. The results improved for all but two of the objectives on the final post-test, indicating that students had retained and were able to apply the knowledge they had acquired. Recall that the questions on the final assessment were more application-oriented to minimize memorization effects. The difference for question 4 was one student, while four students had more difficulty with question 6. On that question, the most common incorrect answer stated that 2s and 3s orbitals were the same size because they both could hold two electrons, perhaps indicating that the students were not thinking of the physical size of the orbitals but the electron holding capacity instead. Students’ performance on Question 5, which asks students to compare the size of orbitals in the same energy level, stands out as being particularly poor. Many of the answers students gave on that question indicated that they did not understand the question

AUTHOR INFORMATION

Corresponding Author

*[email protected] Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS I thank Gaussian Inc. and SemiChem, Inc., for providing the software that made this project possible and Gaussian, Inc. for their support of this work. I also thank J. Sonnenberg (Stevenson University) for trying these activities with upper level college chemistry majors and M. Frisch (Gaussian, Inc.) for valuable feedback.

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