Emphasizing the Significance of Electrostatic Interactions in Chemical

Article pubs.acs.org/jchemeduc

Emphasizing the Significance of Electrostatic Interactions in Chemical Bonding Bhawani Venkataraman* Department of Natural Sciences and Mathematics, Eugene Lang College, The New School, New York, New York 10011, United States S Supporting Information *

ABSTRACT: This paper describes a pedagogical approach to help students understand chemical bonding by emphasizing the importance of electrostatic interactions between atoms. The approach draws on prior studies that have indicated many misconceptions among students in understanding the nature of the chemical bond and energetics associated with bond formation and dissociation. The paper also presents an activity designed to help students conceptualize and demonstrate their understanding of relevant principles. To assess the effectiveness of this approach, a series of pre- and posttest questions and specific questions on the final exam was used to evaluate students’ understanding of concepts. Analyses of this assessment reveal that emphasizing the significance of electrostatic interactions and the role of potential energy in chemical bonding helps students articulate why atoms form chemical bonds. Consequently, students recognize the energetics associated with bond formation and dissociation and are able to apply this understanding to specific chemical reactions. KEYWORDS: First-Year Undergraduate/General, Misconceptions/Discrepant Events, Covalent Bonding

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INTRODUCTION Chemical bonding and reactivity are central concepts in chemistry. Yet, the literature identifies many challenges students face in understanding the nature of a chemical bond and why atoms form chemical bonds.1−17 Some students believe that atoms form chemical bonds to “complete an octet”, atoms are “happy” when they form chemical bonds, or atoms bond because electrons attract.3 Studies also reveal that many students do not understand the interactions that drive chemical bonding11,13,14 or comprehend the energetics associated with chemical bonding.6,7,9,17 Consequently, many students believe energy is released when a bond breaks, energy is required for a bond to form, or that energy is released both when a bond breaks and forms.4,6,7,9,17 These misconceptions are carried over to related concepts such as polarity, noncovalent interactions, and the molecular-level interactions that govern phase transitions.7,11,13,14,18 Electrostatic interactions drive chemical bonding and intermolecular interactions and dictate properties such as electronegativity and polarity. Work by Nahum et al. describes a pedagogical approach that emphasizes electrostatic interactions in chemical bonding and behavior.11,13,14 Their work draws from interviews with chemistry teachers and researchers in chemistry and chemical education where participants were asked to elaborate on their understanding of chemical bonding. These discussions led to their “bottom-up framework” that starts with the individual atom and moves on to interactions © XXXX American Chemical Society and Division of Chemical Education, Inc.

between atoms in forming chemical bonds and then extends this to molecular structure and properties.11,13,14 More recent work explored students’ understanding of the significance of potential energy in atomic and molecular interactions.17 This study concluded that pedagogical approaches should emphasize atomic and molecular interactions and the significance of the potential energy of these interactions to help develop a fundamental understanding of the chemical bond. The study discussed in this paper presents a pedagogical approach that is informed by the work described above and an assessment of the effectiveness of this approach in helping students understand the nature of the chemical bond. The approach is closely aligned with the “bottom-up” framework of Nahum et al.11,13,14 Further, as suggested by Becker et al., the approach presented here emphasizes the significance of electrostatic interactions and the changes in potential energy in chemical bonding.17 The approach emphasizes that atoms are made up of charged particles and that the electrostatic interactions between charged particles dictate the behavior of atoms and molecules. The significance of the potential energy of the electrostatic interactions in formation and breaking of chemical bonds is emphasized to help students understand why atoms form chemical bonds and hence why bond formation is Received: June 2, 2016 Revised: December 18, 2016

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DOI: 10.1021/acs.jchemed.6b00409 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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Table 1. Timeline of Presentation of Key Concepts and Assessment Questions Assessment Questionsa,b

Week and Activity Week 2: Preactivity survey Questions 1, 2, 3 Class discussions: Why do atoms form chemical bonds? Week 3: Homework: “Why do atoms form chemical bonds?” Postactivity survey Questions 1, 2, 3 Week 10: Pre-energetics survey Questions 4 and 5 Class discussions: Energetics and chemical reactivity

Week 11: Postenergetics survey Questions 4, 5, 6

Week 15: Final Exam Question 5 and 7

a

1a 1b 2a

3b

What is a chemical bond? Why do atoms form chemical bonds with other atoms? When a chemical bond is formed between two atoms (for example, between two H atoms), is energy absorbed or released? Explain why. What does “forming a bond” mean? When a chemical bond is “broken” between two atoms (for example, between two H atoms), is energy absorbed or released? Explain why. What does “breaking a bond” mean?

4 4a 4b

Every chemical reaction is accompanied by absorption and release of energy. For a chemical reaction to take place, must reactant molecules absorb or release energy? Explain why.

4c 4d 5 5a i ii iii 5b 6a

Do the product molecules absorb or release energy? Explain why. Consider the following chemical reaction: H(g) + Cl2(g) → HCl(g) + Cl(g) If the reaction occurs with a net release of energy, which of the following is true? The H−Cl bond is stronger than the Cl−Cl bond. The H−Cl bond is weaker than the Cl−Cl bond. The relative bond strengths cannot be determined from the information provided. Briefly explain your answer. Heat is given off when hydrogen burns in oxygen according to the equation: 2H2 + O2 → 2H2O. Which of the following is responsible for the heat given off? Breaking hydrogen bonds. Breaking oxygen bonds. Forming hydrogen−oxygen bonds. Both (i) and (ii) are responsible. Briefly explain your answer. Identify bond formation as exothermic (energy releasing) or endothermic (energy absorbing). Explain why. Identify bond breakage as exothermic (energy releasing) or endothermic (energy absorbing). Explain why.

2b 3a

i ii iii iv 6b 7a 7b 7c 7d

Questions 1a, 1b, 3a, and 5 were drawn from the same published study.6 bQuestion 6a was drawn from a different published study.7

style and capped at 18 students. Data discussed in this study were collected over four semesters, with an average class size of 13 students. As discussed below, since data analysis relied on a student completing multiple components, the sample size for this study was 38. This study received approval from the institution’s IRB; students completed an informed consent form. Table 1 shows a timeline for discussion of concepts and the questions used to assess understanding of relevant concepts. This study was carried out in three stages: 1) “Why do atoms form chemical bonds?”: Focused on class discussions on chemical bonding and the questions used to assess students’ understanding. (2) “Energetics of chemical bonding in chemical reactions”: Focused on class discussions on the energetics associated with chemical reactions and the questions used to assess students’ understanding. (3) “Assessment of student learning”: Analyses of students’ responses to the assessment questions.

accompanied by a release of energy and bond dissociation requires absorption of energy. The following questions guided this study: • Does emphasizing the significance of electrostatic interactions help students recognize why atoms form chemical bonds? • Are students able to apply this understanding to identify energy changes accompanying a chemical reaction? This paper presents an activity designed to help students articulate their understanding of relevant principles related to chemical bonding. The activity also investigates factors that influence bond length and bond strength (e.g., atomic radii and electronegativity). The study compares students’ understanding of chemical bonding as they entered the course to their understanding after class discussions that emphasize the significance of electrostatic interactions and potential energy in chemical bonding. The study also looks at students’ ability to apply this understanding to recognize the energetics associated with bond formation and dissociation and how this influences the net change in energy accompanying a chemical reaction.

Why Do Atoms Form Chemical Bonds?

METHODS This study was conducted in an introductory level, undergraduate chemistry course, the first chemistry course students take at this institution, with a majority (∼80%) having taken chemistry in high school. Classes in this institution are seminar-

Prior to class discussions on the chemical bond, students were asked to complete a survey in class that included questions 1, 2, and 3 in Table 1. This presurvey was used to assess students’ prior understanding of the nature of chemical bonds. Some of these questions were drawn from a published study that demonstrated that students’ responses to these questions were

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helpful in assessing their understanding of related concepts.6 At this point, students were not provided with feedback to their responses to the survey. Instead, as discussed below, class discussions on chemical bonding commenced. Class discussions on chemical bonding commenced following this survey. At this point, the students understood that the atom consists of charged particles and that the electrostatic interactions between electrons and protons define atomic structure. Periodic properties have also been discussed (e.g., variations of atomic radii across a period and down a column). The discussion of chemical bonding began with the class recognizing that most of the atoms that make up materials we interact with and those that make up Earth’s atmosphere exist as compounds and hence have formed chemical bonds with other atoms. The following questions were posed to the class. (i) What is a chemical bond? (ii) Why do atoms form chemical bonds? To answer these questions, the class began by reviewing potential and kinetic energy. The class reviewed why an object falls down when released and the changes in the object’s potential and kinetic energies as the object moves from a higher point to a lower point. Most students remembered the role of gravity and that the potential energy of an object decreases as it falls, with the potential energy being converted into kinetic energy. The students also realized that an external source of energy is required to raise an object and, consequently, raising an object increases its potential energy. The objective is for students to develop an intuitive understanding that the lower potential energy state is a more “stable” state. Raising potential energy requires external energy and results in a higher potential energy, less “stable” state. The next discussion used magnets as an analogy for the influence of electrostatic forces on potential energy. Students were asked to predict what happens to the potential energy of two magnets when the magnets are oriented with opposite poles facing, compared to two magnets oriented with like poles facing. By interacting with the magnets and changing orientations, students experienced the repulsive force between two like poles and the attractive force between opposite poles. From this experience, students recognized that energy is required to force the two like poles close together. However, when the magnets are oriented with the two opposite poles facing, at a certain distance apart letting go of one of the magnets resulted in that magnet moving toward the other. The discussions emphasized that the movement of the magnet when oriented toward the magnet with the opposite pole facing, lowered the potential energy of the magnets, with the potential energy being converted to kinetic energy of motion. These discussions introduced the concept that “attraction” lowers potential energy and “repulsion” raises the potential energy of the magnets. Following the discussions with magnets, students were asked to predict how the potential energy of two hydrogen atoms changes as the atoms approach each other. Through a guided discussion, they recognized that as the distance between the two hydrogen nuclei decreases there is an attractive interaction between the electron of one H atom and the proton of the other. The students then recognized that this attractive interaction lowers the potential energy of the atoms. The question was then posed − “Will this attractive interaction continue for all decreasing distances?” The students recognized that at some internuclear distance, repulsion between the

electrons and between protons limits the distance of closest approach. To summarize these concepts, a plot of the potential energy of the two atoms as a function of internuclear distance was presented on the board (e.g., Figure 1). Visualizing the

Figure 1. Plots showing the potential energy as a function of interatomic distance between an H and F atom (red) and an H and Cl atom (green). Graphs are computed using Spartan Student Edition.19 Note that the values of the calculated bond energies do not agree with experimental values, but relative trends in bond energies are accurately predicted.

potential energy as a function of internuclear distance facilitates an understanding that the chemical bond is formed at the point where attractive and repulsive interactions are balanced and that this balance between opposing forces defines the minimum energy point.11,13,14 The discussion then introduced the concept that energy is “released” when a chemical bond is formed. Since the formation of a chemical bond lowers the potential energy of the atoms, the question is to what form of energy is the potential energy converted? Students were reminded about the conversion of potential energy to kinetic energy of motion when two magnets are oriented with opposite poles facing. In the case of the electrostatic attraction between two atoms that form the chemical bond, the potential energy is converted to the kinetic energy of the motion of the atoms, and that some of this potential energy may also be converted to other forms such as heat. Hence, the “release” of energy associated with forming a chemical bond is a measure of the lowering of the potential energy of the atoms as a result of the electrostatic attraction. Figure 1 shows an example of plots that were introduced to the students. The plots allow students to “visualize” the lowering of the potential energy that accompanies the formation of a chemical bond. This was emphasized to help students recognize why forming a chemical bond is accompanied by a release of energy. Further, students can also visualize why breaking a chemical bond requires an absorption of energy to overcome the electrostatic attractive interactions. Following the class discussion, students were assigned a homework activity titled “Why do atoms form chemical bonds?” to reinforce concepts covered during the class discussions (this activity is included in the Supporting Information). Questions 1−3 in Table 1 asked in the presurvey were also included in this homework assignment. The activity also served to assess students’ understanding of concepts and whether the class discussion had influenced or altered their understanding of the chemical bond compared to their prior understanding. Students’ responses to these questions in the presurvey were compared with the responses in this homework C



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Table 2. Comparison of Pre- and Post-test Scores for Questions in 1−3 in Table 1 Parameters Preactivity Postactivity Wilcoxon z and r values (N = 38)a,b a

Average Scores for Student Responses to Questions, with Maximum Score Possible Q 1a, Max 5

Q 1b, Max 5

Q 2a, Max 1

Q 2b, Max 5

Q 3a, Max 1

Q 3b, Max 5

2.3 4.3 z = 5.3 r = 0.61

2.4 4.1 z = 4.9 r = 0.56

0.4 0.9 z = 4.0 r = 0.46

1.2 4.3 z = 5.1 r = 0.59

0.3 0.9 z = 4.3 r = 0.50

1.3 4.1 z = 5.1 r = 0.58

For all questions, p < 0.01. bEffect size: r = 0.1 indicates a “small” effect; r = 0.3, a “medium” effect; and r = 0.5, a “large” effect.

Table 3. Comparison of Average Scores of Students’ Responses to Questions 4 and 5 in Table 1 from the Pre-energetics and Postenergetic Surveys Parameters Pre-energetics Postenergetics Wilcoxon z, p,, and r values (N = 38)a

a


Q 4b, Max 5

Q 4c, Max 1

Q 4d, Max 5

Q 5a, Max 1

Q 5b, Max 5

0.5 0.8 z = 2.64 p < 0.01 r = 0.30

2.1 3.7 z = 3.53 p < 0.01 r = 0.41

0.7 0.8 z = 0.94 p = 0.35 r = 0.11

2.1 3.3 z = 2.63 p < 0.01 r = 0.30

0.7 0.8 z = 0.51 p = 0.61 r = 0.60

2.4 3.6 z = 2.98 p < 0.01 r = 0.34

Effect size: r = 0.1 indicates a “small” effect; r = 0.3, a “medium” effect; and r = 0.5, a “large” effect.

responses were used to assess how students’ understanding of the energetics associated with chemical reactions had evolved as a result of class discussions and their ability to apply this understanding to specific chemical systems. Students were not graded on the pre- and postenergetics survey nor were comments on their responses handed back to students. Therefore, in essence, students did not know how they performed on these questions. The final exam was administered on the last day of class. Questions 4 and 5 in Table 1 were repeated in the final exam. Note that students did not receive feedback on their prior responses to these questions. In addition, Question 7 in Table 1 was included in the final exam. While concepts relevant to question 7 were discussed in class, this is the first time students were asked to respond in writing to this question. Question 7 draws from the same concepts as presented in questions 2 and 3 in Table 1, but includes terms introduced in the discussion on energetics. Since this was an in-class final exam, students did not have access to any notes or other materials.

assignment. Students were provided feedback and an answer key to this homework assignment to help clarify and correct their answers (see Supporting Information). Students did not have access to their responses to the preactivity survey when they completed the homework activity. Energetics of Chemical Bonding in Chemical Reactions

The concepts that a chemical bond is a result of electrostatic interactions between electrons and protons and that the attractive interaction lowers potential energy when a chemical bond is formed were established in weeks 2 and 3 of a 15-week semester. These concepts were drawn upon when discussions on energetics commenced in week 10 of the 15-week class. At this point in the semester, a presurvey was administered in class to assess students understanding of the energetics associated with chemical bonding in chemical reactions. This presurvey included questions 4 and 5 in Table 1. Terms such as reactants and products had not yet been introduced nor had there been discussions regarding energy changes accompanying a chemical reaction and the role of bond breaking or forming in a chemical reaction. After the presurvey was administered, the class discussions focused on energetics and chemical reactions. Concepts such as chemical change, defining reactants and products in a chemical reaction, and balancing chemical equations were discussed. The role of energy in chemical reactions is related to prior discussions on why energy is released during bond formation and energy absorbed during bond breakage. These concepts were used to understand the change in potential energy accompanying a chemical reaction and how the potential energies of the chemical bonds of reactants and products influence the net change in energy accompanying the chemical reaction. These concepts were used to define exothermic and endothermic reactions. Homework assignments included energetics problems that related these concepts to specific examples and contexts (e.g., understanding why methane is used as a fuel, and explaining why the net reaction describing photosynthesis is endothermic, but the net reaction describing metabolism (i.e., the reverse reaction) is exothermic. The unit ended with students completing a postsurvey in class that included questions 4, 5, and 6 in Table 1. Post

Assessment of Student Learning

Responses from the presurvey and the “Why atoms form chemical bonds” activity (questions 1−3), pre- and postenergetics survey (questions 4−6), and final exams (questions 4, 5 and 7) were scored using a rubric defined for each question in Table 1. Details of the scoring rubric along with sample students’ responses for each question are included in the Supporting Information. The analyses of students’ responses focused on their understanding of electrostatic interactions between atoms that result in a chemical bond, why bond formation is accompanied by a lowering of potential energy and a release of energy, and that overcoming the electrostatic attraction between two bonded atoms to break a bond requires absorption of energy. Students’ ability to apply this understanding to the energetics accompanying chemical reactions was also assessed.

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RESULTS The data in Tables 2−6 are averages of students’ scores for the questions in Table 1. The data were collected over four different semesters when the introductory level chemistry D



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Table 4. Comparison of Scores of Questions 4 and 5 in Table 1 between the Postenergetics Survey and the Final Exam Parameters


Q 4b, Max 5

Q 4c, Max 1

Q 4d, Max 5

Q 5a, Max 1

Q 5b, Max 5

0.8 0.8 z = 0.47 p = 0.64 r = 0.05

3.7 3.9 z = 0.56 p = 0.57 r = 0.06

0.8 0.9 z = 0.94 p = 0.35 r = 0.11

3.3 3.9 z = 1.69 p = 0.09 r = 0.19

0.8 0.8 z = 0.27 p = 0.79 r = 0.03

3.6 4.1 z = 1.21 p = 0.23 r = 0.14

Postenergetics Final exam Wilcoxon z, p, and r values (N = 38)a

a

Effect size: r = 0.1 indicates a “small” effect; r = 0.3, a “medium” effect; and r = 0.5, a “large” effect.

course was offered. Table 2 lists the average scores of students (N = 38) and compares students’ responses to the questions 1−3 gathered at the start of the semester before class discussions (denoted as “Pre-activity” in Table 1) with those of the same students who completed the homework assignment (denoted “Post-activity” in Table 1) included in the Supporting Information section. Table 3 (N = 38) compares scores to the questions 4 and 5 collected before the class discussion on energetics (“Pre-energetics”) with the scores after the class discussions on energetics (“Post-energetics”). Table 4 (N = 38) compares scores for questions 4 and 5 between the postenergetics survey and the final exam. Table 5 (N = 38)

= 22.0 for 2b). Comparison of the pre-energetics and postenergetics data for questions 4a and 4c revealed a statistically significant difference between the results for questions 4a (p = 0.0060, χ2 = 7.6) and statistically insignificant difference for 4c (p = 1.0, χ2 = 0). Comparison of the postenergetics data with the final exam data for questions 4a and 4c revealed that the differences between the two data sets were statistically insignificant (for 4a p = 0.79, χ2 = 0.071; for 4c p = 0.42, χ2 = 0.64).

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DISCUSSION As has been discussed in the literature, students often use the Lewis model of “completing an octet” as an explanation for why atoms form chemical bonds.11,13,14,17 This literature suggests that this demonstrates students do not have a fundamental understanding of the nature of the interactions between atoms that result in a chemical bond. Students do not recognize why bond formation is accompanied by a release of energy, and some students assume that bond breaking releases energy.2,4,6,9 The literature shows that students, even after a semester of chemistry (or more), believe that the formation of a chemical bond is accompanied by absorption of energy and that when a chemical bond is “broken” energy is released.2,7,9 An objective of this study is to assess the effectiveness of the described pedagogical approach, which emphasizes the electrostatic interactions between atoms and the resulting change in potential energy of the interacting atoms.

Table 5. Average Scores of Students’ Responses for Question 6 in Table 1 from the Postenergetic Survey Average Scores for Student Responses to Questions, with Maximum Score Possible

Parameter

Q 6a, Max 1

Q 6b, Max 5

0.7

3.3

Postenergetic survey (N = 38)

lists the average scores for question 6 from the postenergetics survey, and Table 6 (N = 38) lists the average scores for Table 6. Average Scores of Students’ Responses for Question 7 in Table 1 from the Final Exam Parameters

Final exam (N = 38)

Average Scores for Student Responses to Question, with Maximum Score Possible Q 7a, Max 1

Q 7b, Max 5

Q 7c, Max 1

Q 7d, Max 5

0.9

4.3

0.8

4.2

Does Emphasizing the Significance of Electrostatic Interactions Help Students Recognize Why Atoms Form Chemical Bonds?

The preactivity data in Table 2 reveal students’ understanding of chemical bonding as they enter the course, before any class discussions on the chemical bond. As has been discussed above, students were not given feedback on their responses to the preactivity survey. The postactivity data are drawn from students’ responses to questions included in the homework activity “Why do atoms form chemical bonds?”. This assignment focused on the following key concepts: (i) atoms interact through electrostatic interactions as a result of the fact that atoms are made up of charged particles; (ii) a “chemical bond” is a result of attractive interactions between the oppositely charged protons and electrons of the interacting atoms; (iii) attraction lowers the potential energy of the atoms; (iv) the chemical bond between two atoms is defined by the minimum potential energy point where attraction and repulsion are balanced; and (v) the minimum potential energy point defines the bond energy and bond length. All of these concepts are related to questions 1−3 in Table 1. A statistical analysis of the scores of students’ responses collected from the preactivity and postactivity surveys reveals that the postactivity scores for questions 1−3 (parts a and b)

question 7 from the final exam. The data in Tables 2−6 are drawn from the same group of students who completed all parts: the preactivity survey, the homework assignment from which the postactivity data were collected, the pre- and post energetics surveys, and the final exam. A Wilcoxon signed rank test was performed for the data collected at the different points described above with the z- and p-value indicating the degree of statistical significance of the data. An estimate of the effect size, r, for a Wilcoxon-signed rank test was also determined, where r = 0.1 indicates a “small” effect, r = 0.3 a “medium” effect, and r = 0.5 a “large” effect.20 Results of this statistical analysis are included in Tables 2−6. Since the responses to some of the questions (2a, 3a, 4a, and 4c) were binary (absorb or release energy) a McNemar’s test was also performed. The results of the analysis supported the conclusions of the Wilcoxon signed test for these questions. Comparison of the preactivity and postactivity data for questions 2a and 3a revealed a statistically significant difference between these data sets (p < 0.0001 with χ2 = 19.0 for 2a and χ2 E



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are statistically different from the preactivity scores (see Table 2), with r values between 0.46 and 0.61 (r > 0.5 indicates a “large” effect).20 The data show that 100% of the students (N = 38) correctly identified that formation of a chemical bond is accompanied by a release of energy, and 90% of the students recognized that breaking a chemical bond requires absorption of energy (questions 2a and 3a). This is an increase over the preactivity survey where 40% of the students correctly identified that formation of a chemical bond releases energy, and 30% of the students correctly identified that bond breaking requires absorption of energy. Analysis of scores for the questions that asked students to explain the basis of their understanding (1b, 2b, 3b) reveal that the postactivity scores are statistically greater (with r > 0.5) compared to the preactivity scores. By looking at the responses in the preactivity score, common explanations for the question “why do atoms form chemical bonds” included “complete the valence shell” (45%) and “become stable” (29%) without explaining what this means and why bonding may result in increased “stability”. In the postactivity responses, the number of students stating that atoms bond to “complete the valence shell” drops to 3%. Instead, the postactivity answers emphasized the significance of the electrostatic interactions between electrons and protons and the influence of potential energy as a result of these interactions. For example, 74% of the students discuss the significance of electrostatic interactions between the electrons and protons in chemical bonding, compared to 5% of responses in the presurvey. The significance of attractive interactions on lowering of the potential energy is referenced by 76% of the students. The shift away from statements such as “completing the valence shell” to statements that reflect the significance of electrostatic interactions and potential energy in chemical bonding suggests a more refined understanding of why atoms form chemical bonds. This is also reflected in the fact that the majority of students correctly identified that forming a chemical bond is accompanied by a release of potential energy and breaking a bond requires absorption of energy. It must be acknowledged that this is a homework assignment, and students could be reflecting what was said in class. At the very least, however, these data suggest a shift in students’ language of why atoms form chemical bonds and recognition of the influence of electrostatic interactions and potential energy in the stability of the bonded atoms compared to the unbound atoms. The next step in this study was to assess students’ ability to draw from this understanding and apply this to the energetics accompanying chemical reactions.

and 6 require an application of this understanding to specific chemical reactions. Since these questions have not been discussed in class, nor is feedback on their answers provided to students’, analyses of students’ responses to these questions allows an assessment of whether students are able to apply their understanding of the energetics of chemical bonding to these chemical reactions. Questions 7a−d asked during the final exam require students to explain why bond formation is exothermic and bond breakage is endothermic. The data in Table 3 for questions 4a, 4b, and 4d indicate that the postenergetics scores for all these questions are statistically different from the pre-energetics scores (with r values indicating a “medium” effect (r = 0.3 medium effect).20 For question 4c, the pre- and postenergetics scores are not statistically different. The data indicate that in the pre-energetics survey the majority of students (70%) correctly identified that energy is released as product molecules form. Analysis of responses to question 4d, which asked students to explain why, reveals that for the preenergetics survey students are unable to accurately articulate why (average score 2.1/5), whereas after the class discussions, the postenergetics scores reveal a clearer understanding of why (average postenergetics score 3.3/5). Questions 5a and 5b require students to apply their understanding to a specific chemical reaction. The pre- and postenergetic scores for question 5a are not statistically different; however, for question 5b, the scores are different. In other words, students were able to correctly identify that the H−Cl bond is stronger than the Cl−Cl bond. An analysis of students’ responses to question 5b, which asks students to explain the basis of the understanding to 5a, reveals that some students drew from earlier discussions on the effect of atomic radius on the strength of the covalent bond. However, for 5b, the maximum points of 5 were assigned to those responses that related the bond strength of reactants and products to the net release of energy accompanying the reaction, and hence lower average scores in the pre-energetics survey compared to the postenergetics survey. Question 6 was asked in the postenergetic survey. This question was drawn from a published study that developed a chemical concepts inventory to assess students’ understanding of concepts prior to and after completing a semester of general chemistry.7 In this published study, 28% (N = 923) of the students identified the correct answer at the start of the semester, and at the end of the semester 30% of students identified the correct answer.7 The data in Table 5 show that the average score for questions 6a was 0.7 (Max = 1) and 6b was 3.1 (Max = 5), which indicated that 70% of the students correctly identified that the formation of the hydrogen−oxygen bond is responsible for the heat release accompanying this chemical reaction. As with question 5, question 6 required students to apply their understanding of energetics to a specific chemical reaction. Looking at the postenergetics scores for questions 5 and 6 suggests that students are able to relate their understanding of the energetics of bond formation and dissociation to identify correctly the net energy change accompanying chemical reactions and explain why. Questions 5a and 5b are repeated in the final exam, and the data in Table 4 show that students have retained their understanding. In addition, questions 7a−d were part of the final exam. The data in Table 6 show that 90% of the students correctly identify that bond formation releases energy and that bond breaking requires energy. Scores for questions asking

Are Students Able To Apply Their Understanding of Electrostatic Interactions in Chemical Bonding To Identify Energy Changes Accompanying a Chemical Reaction?

The data in Table 3 compare students’ scores from the preenergetics survey in week 10 to their scores from the postenergetics survey in week 11. Prior to the pre-energetics survey, terms such as “reactants” and “products” have not been discussed or that bond breaking and bond formation accompany a chemical reaction. Hence, the data collected in the presurvey reflect the students’ prior knowledge regarding these concepts and terms. Discussions on relevant concepts on chemical reactivity and energetics commenced after the preenergetics survey had been conducted. Questions 4−7 in Table 1 assess students’ understanding of the energetics associated with chemical reactions. Questions 5 F



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bond. To clarify this, the text for the first three selections for question 6a should be (i) breaking the covalent H−H bond, (ii) breaking the covalent OO bond, and (iii) forming the covalent H−O bond. Both these questions have been changed for data collected since this study.

students to explain why (Q7b 4.3/5; Q7d 4.2/5) indicate that they are able to relate the role of potential energy in bond formation and dissociation. Comparison of the students’ results described here with those from published studies supports the recommendations made in the literature for emphasizing the significance of electrostatic interactions in chemical bonding. For example, one study revealed that after a year of general chemistry (and some students had taken organic chemistry as well), 80% of the students believed that breaking bonds in reactant molecules in a combustion reaction was the reason for release of energy accompanying the reaction.8 Other studies came to similar conclusions, that the notion of breaking bonds releases energy is a persistent misconception even after completion of a general chemistry sequence.3,4,6,7,9 Much of this confusion was attributed to students not recognizing the significance of the electrostatic interactions between atoms that define the chemical bond.11,13,14,17 The data from this study suggest that emphasizing the significance of electrostatic interactions and the role of potential energy in the formation of a chemical bond help students appreciate why atoms form chemical bonds. Such an approach shifts students’ prior conceptions (e.g., “completing valence shells”) for why atoms bond. Further, in the three questions asked (questions 5, 6, and 7), students’ responses demonstrate that the majority of students understand the role of potential energy in chemical bonding and can explain why bond formation is exothermic and bond dissociation is endothermic. It must be acknowledged that this study had a small sample size (38 students), and the approach described here was intentional in emphasizing the significance of electrostatic interactions in chemical bonding and how this influences energetics of bonding and chemical reactivity. However, as discussed, this study shows a shift away from students’ prior high school conceptions of chemical bonding to a more accurate model. As the data suggest, this shift appears to be retained through the semester and allowed students to understand concepts that have been identified as challenging for students. This is seen through the two chemical systems presented in questions 5 and 6, and question 7, where the majority of the students were able to recognize bond formation as exothermic, bond dissociation as endothermic, and use this understanding to explain the net change in energy accompanying these chemical reactions.

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CONCLUSIONS The data presented in this paper support recommendations made in the literature that emphasizing the significance of electrostatic interactions between atoms and the energy changes as a result of these interactions helps students understand why atoms form chemical bonds. As a result, students recognize that energy is released when a chemical bond is formed and conversely that bond breaking requires absorption of energy. Students are then able to apply this understanding to explain why the net energy change accompanying a chemical reaction is determined by the difference between energy absorbed by the reactants to break chemical bonds and energy released when bonds are formed in product molecules.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.6b00409. Activity, answer key to activity, scoring rubric used for questions in Table 1 and responses for maximum score, and sample student responses for each question and each score used in the rubric (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Bhawani Venkataraman: 0000-0003-3755-9695 Notes

The author declares no competing financial interest.

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REFERENCES

(1) Peterson, R.; Treagust, D.; Garnett, P. Identification of Secondary Students’ Misconceptions of Covalent Bonding and Structure Concepts Using a Diagnostic Instrument. Res. Sci. Educ. 1986, 16, 40−48. (2) Boo, H. K. Students’ Understanding of Chemical Bonds and the Energetics of Chemical Reactions. J. Res. Sci. Teach. 1998, 35, 569− 581. (3) Coll, R. K.; Taylor, N. Alternative Conceptions of Chemical Bonding Held by Upper Secondary and Tertiary Students. Res. Sci. Technol. Educ. 2001, 19, 171−191. (4) Nicoll, G. A Report of Undergraduates’ Bonding Misconceptions. Int. J. Sci. Educ. 2001, 23, 707−730. (5) Coll, R. K.; Treagust, D. F. Exploring Tertiary Students’ Understanding of Covalent Bonding. Res. Sci. Technol. Educ. 2002, 20, 241−257. (6) Teichert, M. A.; Stacy, A. M. Promoting Understanding of Chemical Bonding and Spontaneity Through Student Explanation and Integration of Ideas. J. Res. Sci. Teach. 2002, 39, 464−496. (7) Mulford, D. R.; Robinson, W. R. An Inventory for Alternate Conceptions among First-Semester General Chemistry Students. J. Chem. Educ. 2002, 79, 739−744.

Future Work

This study provides the basis for more in depth analysis of students’ understanding of chemical bonding and transfer of this understanding to energetics accompanying chemical reactions. Future plans include the addition of different questions in the final exam instead of the ones used during the energetics survey to more clearly assess understanding and application of concepts. Further studies may also include interviews with students to elicit more details of their understanding. Such studies will help provide further validation of the effectiveness of emphasizing electrostatic interactions in bonding. Finally, an outcome of this study was the recognition that some questions in Table 1 need to be reworded for accuracy. Question 4c is more accurate if stated as “Is the formation of products accompanied by a release or absorption of energy?”. Question 6a, response (i) could be confused by a student as referencing hydrogen bonding rather than the covalent H−H G



Article

(8) Coll, R. K.; Treagust, D. F. Investigation of Secondary School, Undergraduate, and Graduate Learners’ Mental Models in Ionic Bonding. J. Res. Sci. Teach. 2003, 40, 464−486. (9) Galley, W. C. Exothermic Bond Breaking: A Persistent Misconception. J. Chem. Educ. 2004, 81, 523−525. (10) Unal, S.; Calik, M.; Ayas, A.; Coll, R. K. A Review of Chemical Bonding Studies: Needs, Aims, Methods of Exploring Students’ Conceptions, General Knowledge Claims, and Students’ Alternative Conceptions. Res. Sci. Technol. Educ. 2006, 24, 141−172. (11) Levy Nahum, T.; Mamlok-Naaman, R.; Hofstein, A.; Krajcik, J. Developing A New Teaching Approach for the Chemical Bonding Concept Aligned with Current Scientific and Pedagogical Knowledge. Sci. Educ. 2007, 91, 579−603. (12) Othman, J.; Treagust, D. F.; Chandrasegaran, A. L. An Investigation into the Relationship Between Students’ Conceptions of the Particulate Nature of Matter and Their Understanding of Chemical Bonding. Int. J. Sci. Educ. 2008, 30, 1531−1550. (13) Kronik, L.; Levy Nahum, T.; Mamlok-Naaman, R.; Hofstein, A. A New “Bottom-Up” Framework for Teaching Chemical Bonding. J. Chem. Educ. 2008, 85, 1680−1685. (14) Levy Nahum, T.; Mamlok-Naaman, R.; Hofstein, A.; Taber, K. S. Teaching and Learning the Concept of Chemical Bonding. Stud. Sci. Educ. 2010, 46, 179−207. (15) Luxford, C. J.; Bretz, S. L. Moving beyond Definitions: What Student-Generated Models Reveal about Their Understanding of Covalent Bonding and Ionic Bonding. Chem. Educ. Res. Pract. 2013, 14, 214−222. (16) Luxford, C. J.; Bretz, S. L. Development of the Bonding Representation To Identify Student Misconceptions about Covalent and Ionic Bonding Representations. J. Chem. Educ. 2014, 91, 312−320. (17) Becker, N. M.; Cooper, M. M. College Chemistry Students’ Understanding of Potential Energy in the Context of Atomic− Molecular Interactions. J. Res. Sci. Teach. 2014, 51, 789−808. (18) Schmidt, H.-J.; Kaufmann, B.; Treagust, D. F. Students’ Understanding of Boiling Points and Intermolecular Forces. Chem. Educ. Res. Pract. 2009, 10, 265−272. (19) Spartan Student ed. Spartan‘16; Wavefunction, Inc.: Irvine, CA., 2016. https://www.wavefun.com/ (accessed November 2016). (20) Pallant, J. SPSS Survival Guide, 4th ed.; Open University Press: Maidenhead, UK, 2010; pp 230−232.

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Emphasizing the Significance of Electrostatic Interactions in Chemical

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