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Keywords:

  • conceptual change;
  • misconceptions;
  • cognitive science;
  • evaluation and theory

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

The connection between the molecular-level structure of a substance and its macroscopic properties is a fundamental concept in chemistry. Students in college-level general and organic chemistry courses were interviewed to investigate how they used structure–property relationships to predict properties such as melting and boiling points. Although student difficulties in this area are well documented, they are usually classified as individual misconceptions. However our studies showed that student problems appear to arise from a complex interplay of problems involving a number of different sources: (1) models of phases/phase change, (2) use of representations, (3) language and terminology, and (4) use of heuristics in student reasoning. No two students used the same sets of ideas to perform the task at hand, and while we did see some recurrences of a single idea or heuristic, the ways that students combined them were different. We believe that, at least for high-level complex tasks such as determining structure–property relationships, student understanding is best understood as a set of loosely connected ideas, skills, and heuristics that are not well integrated. These are not single “misconceptions” that can be reconstructed in isolation. What is clear is that students who have done everything we ask of them, and who have earned high grades in chemistry courses are unable to address a core concept in chemistry. Typical assessments often mask the difficulties that students have with core concepts, since many students may correctly answer a question using heuristics, but have faulty reasoning. We recommend that instruction should include a scaffolded progression of ideas, and opportunities to construct and connect their understanding that will allow students to construct a more coherent framework from which to make predictions about the behavior of matter.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

The relationship between the molecular-level structure of a substance and its properties is a core concept of chemistry and a vital skill for understanding a subject like organic chemistry. The foundational idea that the arrangement of atoms and electrons in a substance directly affects the macroscopic, observable properties of that substance is powerful and can provide students with a scaffold on which to build their understanding of a wide range of chemical phenomena. One of the major goals of effective chemistry instruction, therefore, must be to help students learn the knowledge and skills that will allow them to make the connection between molecular-level structure and macroscopic behaviors in a meaningful way. Without a robust understanding of the underlying ideas that allow the structure–property connection, there is no organizing framework for most of chemistry and students, out of necessity, resort to memorization, and generation of heuristics. Nowhere is this more true than in organic chemistry where literally hundreds of seemingly different reactions and interactions can be introduced within one course. If students are unable to use structural cues to determine how and why molecules interact, we cannot be surprised when organic chemistry is thought to be all about memorization.

Unfortunately, the road from structure to properties (and back) requires a long chain of inferences and the application of sets of rules that may appear to be unconnected to the goal at hand. We have previously reported that students have great difficulty with many of the tasks required along the road from structure to properties, including drawing structures themselves and using structures to predict both physical and chemical properties (Cooper, Grove, Underwood, & Klymkowsky, 2010; Cooper, Underwood, & Hilley, 2012; Cooper, Underwood, Hilley, & Klymkowsky, 2012).

Our goal in the work discussed here was to delve more deeply into the ways in which college students use the molecular-level structure of a substance to predict its macroscopic properties. Before we can begin to address the difficulties that students clearly have, it is important to identify how these problems arise so that more effective curricula and pedagogical approaches may be developed.

Background—Misconceptions, Conceptual Change, and Dual Processing

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

Misconceptions

Most educators would agree that the development of conceptual understanding is a major, yet somewhat elusive, goal of all science education. As the NRC committee on Discipline Based Science Education reports, “it is important to begin by identifying what students know, how their ideas align with normative scientific and engineering explanations and practices (i.e., expert knowledge), and how to change those ideas that are not aligned” (Singer, Nielsen, & Schweingruber, 2012). Indeed conceptual understanding and identifying “misconceptions”1 (sometimes known as alternate conceptions, or naïve ideas) that would hinder student understanding of chemical concepts is a major, active research area in chemistry education. While much of the work on conceptual understanding focuses on younger children (Barke, Hazari, & Yitbarek, 2009; Kind, 2004), it is clear that college students also have a wide range of misconceptions (Bodner, 1991; Duis, 2011; Horton, 2007; Nakhleh, 1991; Nicoll, 2001; Ozmen, 2004; Taber, 2009a). Indeed, over 120 papers on conceptual understanding in chemistry have been published in the last decade (Singer, Nielsen, & Schweingruber, 2012).

In this research, we investigate college students' understanding about how structure affects physical properties. While this is a core concept of chemistry, it has not been the focus of many studies. For example, Smith and Nakhleh (2011) report that many college chemistry students retain the well-documented (Othman, Treagust, & Chandrasegaran, 2008; Pierri, Karatrantou, & Panagiotakopoulos, 2008) misconception that when a substance is melted, covalent bonds are broken (rather than intermolecular forces being overcome). The focus of their study was not the structure of the compounds but rather the process of melting or dissolution. To date, in fact, there has been little research about the origin of such ideas or how students' understanding of structure impacts their models of phases or phase changes.

While there are hundreds of different ideas that have been categorized as misconceptions, their origin and extent differ widely. Chi (2008) has proposed a tripartite classification of incorrect student beliefs, ranging from the level of a single idea to ideas that are robust, pervasive, and stem from multiple sources. Perhaps what is most relevant to chemistry instruction is that the deep underlying ideas of chemistry, upon which the rest of the subject is scaffolded, are rarely based on a single concept, idea, representation, or definition. Even a seemingly simple task requires students to organize and synthesize a huge amount of information. For example, the “misconceptions” that sodium chloride exists as molecules (Taber, 2008) and that bond breaking releases energy (Boo, 1998; Cooper & Klymkowsky, 2013) are widely prevalent, but the sources of confusion are complex. A correct explanation of why sodium chloride does not form molecules or why bond breaking is endothermic, is complex and would require an understanding of a range of ideas and a great deal of cognitive effort. Similarly, the focus of this article, structure–property relationships, requires students to concatenate a sequence of inferences and apply several sets of rules before they can provide a meaningful prediction about structure–property relationships.

Conceptual Change

While a misconception at the level of a single fact may be addressed by revising or rebuilding the idea itself; overcoming flawed mental models involves conceptual change. Mental models are students' internal representations of phenomena and, while they need not be accurate, they must be functional and modifiable. The effectiveness and detail of the user's mental models may be restricted by their previous experiences with a similar task, technical background, and how they think about the system (Genter, 1989; Johnson-Laird, 1983; Justi & Gilbert, 2003). Constructing appropriate mental models is particularly important in chemistry since much of chemistry deals with scales that are not visible.

While much has been written about teaching for conceptual change, there are, in fact, no evidence-based, well-tested theories of conceptual change that are widely accepted (diSessa, 2006). Most researchers agree that students bring a collection of assumptions, ideas, and skills with them. The researchers differ, however, in that some interpret student ideas about concepts as fairly coherent (if naïve or mistaken) explanatory frameworks (Chi, 2008; Vosniadou, Vamvakoussi, & Skopeliti, 2008), while others support an approach in which students construct loosely woven explanations of phenomena from smaller fragments (diSessa, 2008; Hammer, 1996). As diSessa (2006) has pointed out, these different theories may necessitate quite different instructional approaches to enact conceptual change.

If students have a somewhat coherent (but incorrect) theory about a particular concept then it should be possible to establish conditions in which they can “reconstruct” that theory through dialog and appropriate instruction (Posner, Strike, Hewson, & Gertzog, 1982). In contrast, if students possess “knowledge in pieces” and construct explanations that are loosely woven, highly contextualized, and often composed “on the fly”, then different instructional strategies may be needed. For example, Linn (2006) has proposed scaffolded knowledge integration frameworks that may promote more robust and coherent models.

Another possible approach to the development of coherent conceptual development involves learning progressions (Corcoran, Mosher, & Rogat, 2009; Jin & Anderson, 2012; Johnson & Tymms, 2011; Neumann, Viering, Boone, & Fischer, 2013; Schwarz et al., 2009; Wilson, 2009) that explicitly develop difficult ideas in a way that allows students to integrate the fragments and ideas into a coherent whole are also proposed as a way to help students develop more robust and self-consistent conceptual frameworks. It may be the case that both approaches are valid in different situations. In either case, it is important to ascertain the knowledge and assumptions (both explicit and implicit) that students bring with them before any attempt to develop instructional materials designed to improve student understanding. With these ideas in mind, our initial goals were to elicit student ideas about the connection between structure and function, to investigate the origins of these ideas and to see how coherent they were. However, as the interviews progressed, we realized that another factor was emerging: instead of using the methods that they had been taught, to elicit structure–property connections, many students were using self-generated (personal) shortcuts or heuristics.

Heuristics and Dual Processing

Most of the earlier research and proponents of both approaches for promoting conceptual change have been focused on systems with macroscopically observable behavior that are often encountered in physics and physical science instruction or macroscopic biological systems. However, in subjects like chemistry that encompass not only the macroscopic level but also the molecular-level, there is an additional level of abstraction since students are unable to directly observe phenomena and therefore must rely on increasingly complex representational systems to understand concepts, models, and ideas. Because of this abstraction, molecular-level understanding must depend on the representational system used and the students' ability to use it. The difficulty in navigating between molecular, symbolic, and macroscopic domains has long been understood (Johnstone, 1982), but it is exacerbated as the representational systems that must be used to encode information increase in complexity.

Experienced chemists can look at a chemical structure and determine the shape, areas of high or low electron density, types of intermolecular forces (IMFs), acidic hydrogens, and reactive centers almost automatically. But beginning students, ideally, must go though a long sequence: (1) construct an appropriate structure that contains enough information to make further inferences (typically taught using a set of rules) showing where all the bonds and non-bonding electrons are located, (2) translate the two-dimensional structure to a three-dimensional structure (using another set of rules), (3) use knowledge of relative electronegativities of atoms to predict bond polarities, (4) use the three-dimensional structure and bond polarity information to make inferences about the overall polarity of the molecule, (5) use this information to determine the types of IMFs that cause interactions between molecules, and (6) use all this information to predict how molecules will interact (Cooper, Underwood, & Hilley, 2012). So, while the concept that the molecular-level structure can be used to predict properties is central, its application is complex and difficult and we should not be surprised when students struggle, even after several years of college chemistry courses.

In fact, instructors have implemented a range of heuristics that are taught to students to help them construct molecular representations and use them to predict properties. For example, the “octet rule” allows students to construct Lewis structures without having to consider how or why the representation should look this way. “Like dissolves like” allows prediction of what substances will be soluble in a given solvent. Such heuristics allow rapid decisions and predictions to be made without considering the ideas that allowed their development. While they are useful “rules of thumb”, it is important to remember that they are not explanations for a particular phenomenon or concept.

There are only a few studies that have investigated the use and development of such heuristics in chemistry. Taber, for example, has reported on the problems arising from the use of the “octet” rule (Taber, 2009a, 2009b). In addition to heuristics that are explicitly taught in classroom contexts (instructionally derived), it has been shown that students also develop their own heuristics to help them simplify the reasoning that must be used to answer complex questions (Gilhooly, 2004; Roberts, Gilmore, & Wood, 1997). Maeyer and Talanquer (2010) have reported on students' use of heuristics during ranking tasks such as those found on typical general chemistry examinations. Students' thinking was categorized as one of four heuristics: recognition, representativeness, one reason decision-making, or arbitrary trend. These researchers did not explicitly ask students to use the structure of the substance to make predictions and rankings, but rather asked them to discuss the criteria they used to make their decisions. In no case did the students' rankings rise above 20% correct, which may be attributed, in part, to the complexity of the task.

The extensive use of such heuristics has been explained by dual process theories of human cognition, which have been developed in a number of disciplines (Evans, 2003). For example, Stanovich and West (2000) introduced the idea of System 1 and System 2 types of thinking, where System 1 thinking is rapid, automated, and requires less cognitive effort; it is the “default mode” for most processes. System 1 thinking is the source of the well-documented literature on cognitive biases and simple errors (Gilovich, Griffin, & Kahneman, 2002). Most people use System 1 the majority of the time: it allows for the performance of multiple tasks simultaneously, and does not require a great deal of cognitive effort. On the other hand, System 2 thinking is sequential, deeper, and requires effort and attention, resulting in the thinker bearing down on the idea at hand and concentrating hard. One of the difficulties in learning science (or learning anything) is that it is almost always necessary to use System 2 thinking processes and to consciously over-ride System 1.

The use of heuristics or shortcuts allows us to use System 1, the default mode, when considering complex problems, and the heuristics we teach are designed to do just this. It is not surprising, therefore, in situations where an extensive chain of inference is required, such as relating molecular structure to properties, that students may also develop their own heuristics to answer questions rather than rely on their knowledge of scientific principles. While the use of heuristics becomes ever more necessary as the chemistry becomes more complex, and experienced chemists automatically default to them to lessen the cognitive load of a particular task, it is important to remember that they are not explanations. For example, the “octet rule” is very helpful when determining how to draw correct structures, however, it tells us nothing about the reasons for bond formation. Similarly “like dissolves like” is a useful shortcut, but provides no insight into the molecular level processes, energy and entropy changes that are associated with the formation of a solution.

Purpose and Significance of the Study

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

In this study, we interviewed students from general and organic chemistry. We specifically asked how they would use the molecular-level structure to determine physical properties such as melting and boiling point. Our focus was on organic chemistry students since a robust understanding of the principles of organic chemistry is predicated on the idea that students can predict how a substance will behave from an inspection of its molecular structure. We included general chemistry students because it is in general chemistry where these skills are first developed, and we wanted to see how (whether) these skills change over time.

Our goals were to better understand the process by which students determined properties such as relative melting or boiling points from a structure and what factors they took into consideration (i.e., molecular geometry or polarity). While other studies have looked at student reasoning about relative phase change temperatures or solubilities (Maeyer & Talanquer, 2010; Smith & Nakhleh, 2011), none have explicitly probed students' understanding of how and why the structure determines these properties. Therefore, we decided to use simple structures so that we did not overwhelm the students. For example, while some common substances like fats and sugars may be familiar to students, their structures may be too complex for a novice to analyze. We believe this study is important because it probes a fundamental construct of chemistry that all students should have mastered by the time they finish general chemistry. In most general chemistry courses (and certainly the courses that these students were enrolled in) the topics covered by our interviews make up about 25% (5 chapters out of 20 chapters that are taught), and approximately 50% of the material in a first semester general chemistry course. Indeed, by the time students reach organic chemistry, most instructors spend little time on the development of these skills because they are such an integral part of the prior knowledge that is expected. While most organic chemistry textbooks do briefly review structure-property relationships in the first chapter, the majority of the course is taken up with more advanced concepts that build on these ideas. For example, how molecules interact to produce new products, how changes in molecular structure and interactions are related to energy changes, and how the three-dimensional structure can be represented and understood in two-dimensional drawings. All of these ideas and skills are predicated upon the kind of understanding that we were probing in this study.

This study is part of a larger series of studies in which we have used a variety of methods to investigate student understanding of molecular structure and properties. In our earlier studies, we investigated whether students were able to draw and use chemical structures to make predictions about properties (Cooper, Grove, Underwood, & Klymkowsky, 2010; Cooper, Underwood, & Hilley, 2012; Cooper, Underwood, Hilley, & Klymkowsky, 2012). The study on which we report here aims to elucidate why students have such trouble with this concept. Using a basic, qualitative research design, a semi-structured interview protocol was implemented to further investigate students' ideas about structure–property relationships. Taken together, these studies consist of a mixed-methods sequential explanatory study (Creswell & Plano Clark, 2007).

Our study focused on two research questions:

  1. RQ 1: Do students use molecular-level structures to make predictions about the macroscopic properties of a substance, and if so how?
  2. RQ 2: How do students enrolled in general and organic chemistry use representations of chemical structures to make predictions about macroscopic properties of substances?

Methods

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

Setting and Participants

This study was conducted at a public southeastern research university of about 20,000 students. At this university, general chemistry and organic chemistry are taught in lecture sections of between 100 and 150 students. Approximately 1,500 students enroll in general chemistry per semester and 600 in organic chemistry. Participants were volunteers who were solicited by email from second-semester general chemistry students (GC2, N = 7), first-semester organic chemistry students (OC1, N = 5), and second-semester organic chemistry students (OC2, N = 5). In order to participate, students must have completed at least one semester of general chemistry; this was to prevent undue confusion for students who had not yet been exposed to topics relevant to understanding the relationship of structure and property such as polarity and intermolecular forces. All of these students signed informed consent forms.

Of the 17 participants, 5 were male and 12 were female; 11 participants pursued biology-related majors, 3 were chemistry majors, and 3 were engineering majors. All participants received either an A or a B in prior chemistry coursework. All of the students were enrolled in either chemistry courses that either “covered” the material (general chemistry) or depended on students knowing these ideas (organic chemistry). The students came from different courses taught by different instructors, using different pedagogies. In general, most students in these courses completed on-line homework assessments and in class written quizzes where they would write or draw a response, often after group discussion. In general chemistry, all the course examinations were multiple choice, but in organic chemistry typically about half the examination was composed of student constructed responses. All students in these courses took final examinations in the form of American Chemical Society normalized examinations (American Chemical Society, 2013) and, on average, scored above the national norm. It is important to state here that these are students who have done everything that is asked of them, and who appear to have a firm command of the material when traditional assessments are used. What follows is in no way intended to imply that the problems we uncover lie with the students. As we will discuss later, we believe it is the structure of the curriculum and the accompanying assessments that do not provide an appropriate learning environment in which students can be expected to develop these complex ideas.

Interview Protocol

The semi-structured interview protocol began by asking students what kinds of tests they might use in a chemistry laboratory to identify a substance. This was to help students recall chemical and physical properties with which they might be familiar. If students did not spontaneously respond with melting point or boiling point tests, the interviewer suggested that such properties were measurable in the laboratory. Students were then asked specifically, in reference to water, ammonia, and ethane, about the types of properties the compound might exhibit. These were compounds that were (or should have been) familiar to the students. The interviewee was then asked to construct a Lewis structure or other structural representation for these compounds and asked how they might use that structure to help them explain the properties (particularly melting point or boiling point) of that compound.

The second portion of the interview was designed to reflect the types of questions the students would typically experience in their chemistry course. Students were given several pairs of compounds and asked to pick, for each pair, the compound that would have the higher boiling point and explain why. Table 1 lists each of the pairs given and the reason why they were chosen. The table also includes reasoning that we would expect a student to use when explaining why one compound would have a higher boiling point than the other. The compounds chosen for discussion were simple structures containing no more than two carbon atoms. It should be noted that if students had difficulty constructing any of these structures throughout the protocol, the interviewer would provide the student with structural cues such as clarifying dimethyl ether as CH3OCH3.

Table 1. Pairs of compounds presented to students, the reasons for choosing this comparison, and the expected student reasoning
Pairs of CompoundsReason for Our ChoiceExpected Student Reasoning
CH3CH3 and CH3CH2OHDifferent molecular weights, different types of IMFsEthanol has a higher boiling/melting point because it has stronger intermolecular forces (specifically hydrogen bonding and dipole-dipole), which require more energy to overcome during a phase change
CH3OH and CH3CH2OHDifferent molecular weights, same types of IMFsEthanol has a higher boiling/melting point because it has stronger London dispersion forces, which require more energy to overcome during a phase change
CH3CH2OH and CH3OCH3Structural isomers, same molecular weights, different types of IMFsEthanol has a higher boiling/melting point because it has stronger intermolecular forces (specifically hydrogen bonding), which require more energy to overcome during a phase change

Data Collection

A post-doctoral researcher conducted the first five interviews and was then joined by a graduate student. After co-conducting four interviews, the remaining eight interviews were conducted by the graduate student (the second author on this article). The length of the interviews varied from 30 to 60 min depending on the amount of information that the students provided. For the interviews, audio and student-constructed representations were collected using a LiveScribe pen, which can replay both the audio and student drawings in real-time (Linenberger & Bretz, 2012). Audio was also recorded using a digital voice recorder.

Data Analysis

After the interviews were conducted, a post-doctoral researcher, an undergraduate research assistant, and a graduate student transcribed them verbatim. Using a qualitative approach based on grounded theory techniques, a graduate student, a post-doctoral researcher, and a faculty member analyzed the interview transcripts and LiveScribe data for emergent themes and commonalities using open coding (Corbin & Strauss, 1990). Initial codes were created and revised via constant comparison (Glaser & Strauss, 1965). Multiple revisions were required in order to address the complex nature of student knowledge of the structure–property relationship. After several iterations of coding, four over-arching themes were identified that encompassed the major issues experienced by students in their explanations of this relationship. Although these themes stemmed from widely differing sources, each was identified as contributing to student difficulties and emerged during the reasoning tasks. These themes are: (1) inappropriate models of phases/phase change, (2) representational difficulties, (3) language and terminology issues, and (4) use of heuristics in student reasoning (whether appropriate or not). Each of these themes in student difficulties consists of a number of subcategories that we collapsed together to produce the major concept.

Findings

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

Emergent Themes in Students' Difficulties in Reasoning Structure–Property Relationships

In response to our first research question (RQ 1), we present examples of each overarching theme that emerged from the interviews and then illustrate how these themes combined and were used by students to make predictions about melting and boiling points of various substances. Table 2 presents each student's pseudonym, their level of chemistry, and which of the four main over-arching themes were present for their reasoning.

Table 2. Students' pseudonyms, chemistry course, and themes that arose during their interview. A count is shown for a specific category if the student showed at least one instance of the code during their interview
PseudonymCoursePhase/Phase ChangeRepresentationsTerminologyHeuristics
PersonalInstructionalMore Means More
NoahGC2101111
BrittanyGC2101011
TinaGC2111110
SusanGC2001100
ErinGC2010010
LucyGC2011110
JustinGC2010101
RobinOC1010111
TedOC1001111
LilyOC1111111
MarshallOC1101101
VictoriaOC1001001
DaisyOC2101101
JoyOC2011111
JillOC2111101
JaneOC2101101
JoeOC2011011

Models of Phases or Phase Change

Eight of our interviewees did not possess a coherent model of the structure of solid, liquid, and gaseous simple molecular compounds, which typically emerged when students were asked to draw structures representing different phases.

Joe (OC2) struggled with drawing a molecular-level depiction of a solid. He seemed concerned about the idea that ethane might form a solid because, if ethane did form a solid, this would require the molecules to be bonded together rather than interacting. “I would say they, if you're saying there is a solid, I guess they would have to bond… because they're just so compact”. He attempted to draw his idea of what bonded ethane would look like in the solid phase, with molecules bonded together, as seen in Figure 1a.

image

Figure 1. (a): Joe's depiction of solid ethane, (b): Jill's depiction of solid ethane, and Brittany's representation of (c): water going from the solid phase to the liquid phase, and (d): water going from the liquid phase to the gaseous phase.

Download figure to PowerPoint

Similarly, Jill (OC2), experienced difficulties depicting solids and liquids on the molecular-level. Her representations of solids and liquids appear to show that they are covalently bonded in a network structure rather than held together via intermolecular forces. Jill was quite consistent with her depictions of solids as networks, as seen in Figure 1b with solid ethane, using the same idea for water, ammonia, and dimethyl ether.

While Jill and Joe experienced difficulties explaining their model of phases, Brittany (GC2) struggled to explain the process of a phase change. When asked explicitly to describe the process of ice melting on the molecular-level, she responded, “Hold on, I've never thought about all this stuff before”. Brittany stated that the “bonds” between the molecules would break, which would leave behind individual water molecules. “Umm I guess it's, I guess maybe the bonds are stronger in a solid and they're weaker in a liquid so it's like, so it's like move, like water like moves and ice doesn't. So it's like movable I guess. Malleable”.

It is well documented that students often confuse intermolecular forces with covalent bonds (Henderleiter, Smart, Anderson, & Elian, 2001; Othman et al., 2008; Taber, 2002), and it is entirely possible that Brittany was confused about the difference between intermolecular forces and covalent bonds, but her structural representations of water in the solid and liquid state still contain water molecules. As she discussed the transition to a gas, however, Brittany broke the covalent bonds within the water molecules; she drew structures for us that clarified what she meant, clearly showing interactions between molecules breaking from solid to liquid and H–O covalent bonds breaking from liquid to gas as seen in Figure 1c,d.

Each of these students struggled with their understanding of either phase or phase changes. They each provided different representations in an attempt to explain their model, but in doing so, they became aware that something was wrong. Their inability to construct appropriate representations and extract meaning from them severely hindered their understanding. If students cannot provide an appropriate representation for each phase, it is unlikely that they will be able to make predictions about relative phase change temperatures or the factors that affect phase changes.

Use of Representations

Nine participants experienced some form of representational difficulty during their interview, although not all were directly related to phase or phase changes. Looking back at Jill's network model of solid ethane in Figure 1b, it is understandable that she explained the process of boiling in terms of bond breaking since her representations made no reference to intermolecular forces. She indicated in her interview that, as a solid melted, some of the bonds were broken. Then, as the substance moved into the gas phase, the individual molecules separated. Her difficulty with this concept was apparent, since there were numerous false starts in her attempt to explain the bonds that break during the boiling process of dimethyl ether:

Like if you broke this (C–H bond in Figure 2a) you'd have two dimethyl ethers versus (Figure 2b) one dimethyl ether and one anhydrous, or one with a partial negative charge on each carbon. I don't know, I can't, I don't know which way is right on that. I suppose that I've never really thought about… this makes, this sounds better (pointing to Figure 2b).

image

Figure 2. (a and b): Jill's first and second attempts at depicting dimethyl ether transitioning from a solid to a liquid and (c) Lucy's representation of non-polar dimethyl ether.

Download figure to PowerPoint

Her first approach, Figure 2a, is consistent with the lattice form she drew for previous compounds in the interview. With this representation, she realizes that, by breaking bonds during the boiling phase change, she would have resulting dimethyl ether molecules missing hydrogens. In her second approach, Jill redraws her lattice structures, connecting dimethyl ethers with covalent bonds between the hydrogens. While this solves the problem of losing hydrogens in the boiling process, she voices concern that now each hydrogen would have two bonds and hydrogen “like it's only got the one electron, one you know so it can only technically bond to one thing”. It is important to note that she refers to the tendency for hydrogen to only form one bond as the rule of hydrogen bonding (a possible terminology issue). She understood that network structures did not make sense for her solids, but, as she stated, “umm I haven't really thought about that” despite the fact that she is in her fourth semester of college level chemistry.

A subtler problem emerged from Lucy (GC2), who knew that the strength of the IMFs determines boiling points. Her problem, however, originated with her difficulties in translating the two-dimensional Lewis structure into a three-dimensional shape. Since she drew dimethyl ether as linear (Figure 2c), she believed that it was non-polar because the bond polarities cancelled:

So if you were gonna kind of split this up, oxygen obviously has the slight negative charge and carbon's gonna have like a slight positive charge but if this is going this, umm opposite ways, it goes towards the negative and then if this is going (drawing) towards the negative then these two arrows cancel each other out.

In fact, only three of the students, all of whom were in general chemistry, used bond polarity vectors to determine molecular polarity and the resultant types of IMFs.

Language and Terminology

It has been well documented that students often struggle with the use of scientific language in their chemistry courses (Johnstone & Selepeng, 2001). Some of this difficulty stems from the use of words that have not only a specific meaning in chemistry, but also a more colloquial use. For example, students may say that a reaction has come to equilibrium but not understand that the process is still ongoing or that the use of the term volatile, commonly meaning explosive or unstable, is used in science to indicate a substance that is easily vaporized.

Most of the participants (14 out of 17) experienced some form of terminology and language problems. During our interviews, it became clear that many were confused about the meaning of words that describe interactions such as bonds, intramolecular forces, and intermolecular forces (such as hydrogen bonding, dipole–dipole, and London dispersion forces). Jane (OC2) was aware that these terms are easily confused:

Umm hydrogen bonding is between if, is it intermolecular force? I always get confused if it's inter or intra because they're two different things but it's between two molecules and it's umm, my professors always do like the little dotted line that shows like the attractions.

That is, Jane, while not sure of the name for intermolecular forces, did understand that these interactions are between two molecules.

Joy (OC2), on the other hand, illustrated hydrogen bonding as both within and between molecules while drawing her structure for ammonia.

Interviewer: Ok. So could you just show me how it hydrogen bonds?

Joy: Oh it's right there between the H and the N. Yeah. I don't know how I just…

Interviewer: So if you had another ammonia molecule could you draw another one for me?

Joy: (drawing additional ammonia with dashed line between the molecules)

Interviewer: Ok so umm what would this be? Like that, you just drew dotted?

Joy: Oh this is a hydrogen bond.

Interviewer: Ok. And you said that this (indicating the N–H bond) is also a hydrogen bond?

Joy: Yeah.

Her depiction of hydrogen bonding, seen in Figure 3, showed both an interaction between the nitrogen of one ammonia molecule and the hydrogen of another as well as the N–H bond within one molecule (indicated by positive and negative charges). Joy's confusion about the term hydrogen bonding is understandable, since, typically, the term bond is used between two atoms in a molecule. At the same time, she also remembered hydrogen bonding as existing between two molecules. To compromise these two ideas, she decided that it could be both.

image

Figure 3. Joy's depiction of hydrogen bonding in ammonia, both within a molecule and between two molecules.

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Unfortunately, the idea that intermolecular forces are what most textbooks refer to as covalent bonds was quite pervasive. Ted (OC1) also struggled with this idea. At the beginning of his interview, Ted referred to hydrogen bonding as the bond between oxygen and hydrogen within the water molecule rather than an interaction between two water molecules. This became a significant terminology problem that followed him throughout his interview as seen when he later compared the relative boiling points of ethanol and ethane:

Umm well you know this one's (ethanol's) going to have the higher boiling point because it's got a strong, the hydrogen bond that's in it right here is going to be a lot stronger to break. So, I mean its going to be more difficult to break since it's a lot stronger bond so you automatically have higher, a higher boiling point than this (ethane).

After further questioning from the interviewer about what specifically breaks when a substance boils, Ted realized there was an inconsistency in his prior reasoning and the bonds within a molecule should not be breaking. He then proceeded to describe an attractive force present between the molecules, but, since he had already allocated the term hydrogen bonding to the O–H bond, he called this force a Van der Waals interaction:

I'm guessing there is not a bond between these two (ethanol's) but there is like a little bit of maybe, not even London dispersion, but there's like an attraction since this is a partial negative side of the polar and this is the partial positive… I don't even know why I am thinking like London dispersion cause that's like within the molecule I want to say or maybe it's, hold on, let me umm… Van der Waals interactions.

While Ted correctly identified that there are attractive forces between two ethanol molecules and had an understanding of the underlying concept of intermolecular forces, his difficulties with terminology created challenges for him in communicating this knowledge. Presumably, this terminology issue could also create problems in making sense of lectures, notes, and textbook content. It should be noted that he described hydrogen bonds and London dispersion forces as within—molecule interactions and Van der Waals forces as between—molecules interactions.

These examples of student difficulties related to representing and communicating phases and phase changes were not unique to the students discussed here. Sometimes the students' issues with phases occurred in combination with their difficulties in producing appropriate representations or terminology issues. Each of these problematic areas combined with others in slightly different ways, making each student's response unique.

Use of Heuristics in Student Reasoning

In the second half of the interviews, students were given the three prediction tasks shown in Table 1 and were asked to explain their reasoning. We anticipated that students would construct structures, use them to predict the types and strengths of intermolecular forces present, and then use this information to predict which compound would take more energy to separate the molecules, which they would relate to the boiling or melting point. What emerged for all students, on at least one occasion, was a heuristic that had either been instructionally derived or personal. Interestingly almost all of the heuristics used some version of what may be akin to diSessa and Hammer's “more means more” p-prim (diSessa, 1993; Hammer, 2000), that is, they almost all involved counting something, be it oxygens, carbons, hydrogens, bonds or intermolecular forces, and used these surface level characteristics to predict properties. While some of these heuristics lead to a correct prediction, many of them did not and several were complicated by problems with representations and language that we have already discussed.

Heuristics—Instructionally derived. Victoria (OC1) is an example of one student who used a heuristic that she had been taught for reasoning about the differences in boiling points of ethanol and dimethyl ether. She discussed how the presence of oxygen is important to compare the boiling points:

Yeah because they both have one oxygen in them… I was always taught that if there was an oxygen in there the boiling point is going to be higher… than if there wasn't an oxygen and if it was an alcohol it would be higher than ether because of the hydrogen bonding.

In this instance, Victoria relied on sets of heuristics to rationalize the difference in boiling points. While she arrived at a correct conclusion, she did not explain the differences in terms of intermolecular forces. Her reasoning is surface-level, as with many other students, in that it focused only on the elements and functional groups present, but it did bring her to the correct conclusion.

Heuristics—Personal. Interestingly, more students (N = 10) used a personal heuristic in comparison to an instructionally derived heuristic (N = 7). For example, Joy (OC2) developed a similar heuristic to Victoria that relied on the presence of oxygen in organic compounds to determine the relative boiling point. Unlike Victoria, however, Joy's version of this heuristic indicated a lower boiling point when oxygen is present. “I wanna say this one (ethanol) has an O, a hydroxyl group on it so I feel like it would boil quicker than the hydrocarbon”. While she never explained her reasoning for this relationship, she later changed her explanation (and her prediction) to include hydrogen bonding when asked to draw out the Lewis structure (including drawing out the O–H group) for ethanol. When questioned about why she changed her reasoning, she replied “Well I wasn't really thinking about it then. I just looked”. In this situation, Joy was even aware herself that she defaulted to a System 1 level thinking and that only after further prompting did she take it a step further to discuss hydrogen bonding.

A few students used a phenomenological approach, indicating that heavier molecules would have a higher boiling point because heavy molecules would be harder to get into the gas phase. Justin (GC2) invoked an instructionally derived “more means more” heuristic when he compared the boiling point of methanol and ethanol. “I think it's [ethanol] a bigger molecule so it, every property increases except for viscosity. That's what, that's what I memorized at least”. Robin (OC1), however, used a personal variant of this “more means more” reasoning: “So it's (methanol) a much smaller molecule first off and it's a lighter molecule… so it will be umm it will go to the gaseous state more readily so it will have a lower boiling point”. Robin's ideas may stem from an inappropriate application of gravitational effects, which are negligible at the molecular scale, or may simply be another p-prim—heavier things are hard to move (diSessa, Gillespie, & Esterly, 2004). Robin was incorrect in her predictions for ethanol and dimethyl ether, presumably because her heuristic was not useful for molecules with the same molecular weight.

In a number of cases, the representational or language issues that led to difficulties with student models of phases were also folded into the reasoning that students used to support their heuristics. For example, some explanations were predicated on a model in which covalent bonds must be broken to change phase. Joe (OC2) used a “more means more” heuristic to explain that the number of bonds within a molecule directly effected the boiling point: “This carbon (ethanol) is more substituted so I would say this carbon (methanol) has a lower boiling point… it has less bonds to break”. Here, Joe indicated that ethanol had more bonds, which he believed would be broken as the ethanol was vaporized. Thus, his understanding seemed to be that ethanol had a higher boiling point because more bonds require more energy to break.

Jane (OC2) also used a similar personal “more means more” heuristic to compare the boiling points of ammonia and water, but she used the number of hydrogen bonds as part of her reasoning. “Because it [ammonia] has more, more bonds… The nitrogen has attached to three hydrogens but the oxygen's only attached to two… More bonds means more intermolecular forces so it should be, it should have a higher melting point”. Jane (as discussed earlier) used the number of hydrogen bonds to predict that ammonia has a higher melting point than water. Her reasoning still involved breaking bonds during a phase change (which she called intermolecular forces).

Comparing General and Organic Chemistry Students' Reasoning of Structure–Property Relationships

In reference to our second research question (RQ 2), it is clear that organic students performed no better than general chemistry students on these tasks, as seen in Table 2, despite their extra semester or two of chemistry. While this may be understandable, since instruction in organic courses typically does not dwell on material that students have presumably mastered in earlier courses, it means that organic students do not have a stable foundation on which to build their new knowledge. The major difference we found between the general chemistry and organic chemistry students was that the organic chemistry students' explanations were often more convoluted because they brought extraneous information to their discussions. For example, while comparing the relative boiling points of methanol and ethanol, Jill (OC2) originally determined that ethanol had the higher boiling point but then changed her mind:

Jill: … I retract my previous statement. I think methanol maybe has a higher boiling point because this one's got more like steric hindrance like between the hydrogen bonds because the molecule's bigger so it's gonna be easier to break.

Interviewer: Ok. How would you break it? What do you mean when you say break?

Jill: Like when you add heat to it or something it's gonna split up the, like all the bonds like if you were you're in a liquid phase you've got all these bonds here that are kind of crammed together and if you heat it up it's gonna start splitting all these bonds apart. You're gonna lose, lose water I guess.

Jill stated that “steric hindrance”, depicted in Figure 4a, caused ethanol to be less stable than methanol. It is unclear whether she was confusing steric hindrance with steric strain, but she believed that when these substances boiled, bonds were broken. She again invoked steric hindrance to correctly predict that ethanol would have a higher boiling point than dimethyl ether:

‘Cause these bonds are gonna be stronger than a carbon, carbon like these two bonds (C–O and O–H bonds) are gonna be stronger than a carbon–hydrogen bond and then this one (dimethyl ether) has got uhh, even more steric hindrance than that one (ethanol) so these bonds are going to break easier.

image

Figure 4. a: Jill's representation of the steric strain in a molecule of ethanol and (b) Lily's depiction of hydrogen bonding between two water molecules indicated by the arrows showing an electron pair leaving and a hydrogen attaching.

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Jill offered up yet another organic chemistry idea to explain why ethanol would have a higher boiling point than ethane:

Because alcohols, the alcohol group is a poor leaving group so it's, the bond's not going to be broken as easily. You'd have to protonate it first and turn it into water and then make it a leaving group. I think… Like the carbon–oxygen bond would be umm more difficult to break than a carbon–hydrogen bond.

For her explanation, Jill continued to discuss the idea of bond breaking when ethanol and ethane underwent the boiling process. Instead of explaining in terms of steric hindrance, however, she used the idea that –OH (alcohol) groups are poor leaving groups and, as a result, would make the carbon–oxygen bond harder to break. Here we have a confluence of a problematic model of phase change involving bond breaking combined with extraneous knowledge and a lack of distinction between a chemical reaction and a phase change.

Although Jill clearly has many problems, Lily (OC1) was the only student interviewed who exhibited at least one instance of every theme outlined in Table 2. When asked about water and how two water molecules would interact:

It would… umm… so yeah… this being the oxygen being the partially negative and the hydrogen being the partially positive like this bond right here (electron pair bonded to the oxygen) is going to break so that this proton (hydrogen on the interacting water) can come in and so like they are going to bond like that.

It quickly became apparent that Lily saw hydrogen bonding as a reaction in which the electron pair on the oxygen would leave so that the hydrogen on another water could come in and form a hydrogen bond, as seen in Figure 4b. She had stated earlier in the interview that hydrogen bonding was a bond within the molecule so her confusion is understandable. Inspection of her drawing showed that Lily was using the arrow notation learned in organic chemistry to mean two different things (neither of which was correct). The top arrow showed the electron pair “leaving” and the bottom arrow showed the hydrogen moving to take its place. It was here that her confusion about the notation used in organic chemistry became apparent. This problem then led to her unique explanation of what happens to water as it changes phase from liquid to gas:

Interviewer: Why would it (water) have a high boiling point?

Lily: Because it takes a lot of energy to break the strong hydrogen bond hold.

Interviewer: So which, can you just point to on the paper which bond you would be breaking?

Lily: Umm you're going to be breaking the bond between these electron pairs so that they can go and that these protons can come in.

Daisy (OC2) used the concept of stability of different types of carbons for her reasoning that ethanol had a higher melting point than methanol: “there's two carbons here they help stabilize each other so it, and over-, and all it has, it's a more stable molecule versus the methanol”. When prompted by the interviewer to explain, Daisy elaborated: “Umm well you typically think of it as the more the carbons the more stable in a way”. It became clearer that she did not think the bonds were breaking, but that carbon–carbon bonds stabilized the molecule somehow, so that it took more energy to boil. She linked this stabilization to what she had learned about stabilization of carbocations in organic chemistry. “This is a primary carbon so it has at least one carbon attached to it. And I know that as you increase that like methyl, primary, secondary, tertiary your stability increases”.

Discussion

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

As Table 2 shows none of the students provided a completely coherent view of how to predict properties from structures. Interestingly though, most students were able to correctly predict which of each pair would have the highest melting or boiling point as shown in Table 3, even though they used some rather surprising reasoning strategies.

Table 3. Student predictions for highest boiling point in each comparison from the second half of the interview protocol
PseudonymEthanol vs EthaneEthanol vs. MethanolEthanol vs. Dimethyl ether
NoahEthanolSimilarEthanol
BrittanyEthanolEthanolEthanol
TinaEthanolNot sureDimethyl ether
SusanEthanolMethanol (but almost the same)Ethanol
ErinEthanolEthanol (but almost the same)Ethanol
LucyEthanolEthanolEthanol
JustinEthanolEthanolEthanol
RobinEthanolEthanolDimethyl ether
TedEthanolEthanolEthanol
LilyEthanolEthanolDimethyl ether
MarshallEthanolEthanolFirst dimethyl ether, then ethanol
VictoriaEthanolEthanolEthanol (but almost the same)
DaisyEthanolEthanolDimethyl ether
JoyFirst ethane, then ethanolEthanolDimethyl ether
JillEthanolFirst ethanol, then methanolEthanol
JaneEthanolEthanolDimethyl ether
JoeEthanolEthanolDimethyl ether

The only pair of compounds that more than two students predicted incorrectly was ethanol and dimethyl ether, presumably because the very common heuristic “more means more” was not applicable. Therefore, students were forced to move to explanations involving IMFs (typically hydrogen bonding) to provide a reason. When intermolecular forces were discussed, terms like hydrogen bonding and London dispersion forces were often used incorrectly (Figure 5). Even students who seemed to have a robust understanding of structure–property relationships had some discrepancies in their reasoning process. Erin (GC2, a bio engineering major) was one of the most articulate and accomplished students; she was able to correctly predict most of the properties of a compound by considering polarity and intermolecular forces. Interestingly, she used her prior knowledge in biology to reason through less familiar topics. For example, she provided a spontaneous (and quite sophisticated) discussion of London dispersion forces using a phospholipid bilayer as an example:

It's a phospholipid bilayer… So what happens with the tails is umm at certain points of time, which is not very often but it does occur, that uhh by chance the electrons line up on one side just because they're constantly moving around and then that creates a very slight negative charge and that influences this one. So then that causes the electrons to be repelled and it causes a slight positive charge and so you have these moments when umm they're attracted because of partial negative and partial positive. But they only occur a very few time periods.

image

Figure 5. Erin's depiction of London dispersion forces in the phospholipid bilayer.

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Even though Erin had a robust understanding of IMFs, she was not clear about the relationship between polarity and shape. Rather than the shape of the molecule influencing its polarity, she reasoned that the opposite is true. When discussing water's polarity and shape, she mentioned that “the shape is more characteristic of the fact that it's polar… it's because, that it's polar that it makes that shape (bent)”. This caused her problems when later reasoning about dimethyl ether since she thought it was non-polar, thus making it linear.

From our interviews, with students who have been successful in their chemistry courses, it is clear that most have significant issues that impede their understanding of the relationship between structure and properties and that the situation does not appear to improve for students who have taken organic chemistry. Despite being specifically asked how they determine the properties of a substance from its structure, few students were able to extend their ideas to predicting and almost invariably invoked a heuristic. It was striking that, even though some students used heuristics that appeared to be very similar on the surface (e.g., “more means more”), they came to quite different conclusions using the same ideas.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

What emerged from our interviews was a diverse tapestry of student thinking. Some students based their predictions on one overarching idea (“more means more”), some wove their model together from disparate facts and ideas, some students were hindered by their inability to construct and use structural representations, and some were hindered by language—either misremembered or misunderstood. Each student constructed a different set of explanations and even those who had one overarching theme used it differently to come to different conclusions.

The major findings of this study are:

  1. Each student individually constructed a different approach to the task posed. These approaches were hindered by other factors that interacted with each other in different ways.
  2. Even students who used what appeared to be a similar approach (e.g., “more means more”) came to different conclusions, using reasoning strategies and heuristics that emerged during the course of the interview.
  3. Students in organic chemistry seemed no more able to make the structure–property connection even though some students could answer questions correctly without consciously reasoning through the process.
  4. Organic students sometimes used their extra knowledge inappropriately, for example, citing “steric hindrance” as a cause of differences in phase change temperatures.

What seems clear is that, as we move forward, simply categorizing “misconceptions” is not enough. The ideas and reasoning that students constructed were a result of the interactions between their understanding of what words mean, what structures mean, their models of how phase changes occur, and their willingness and ability to delve deeply into the underlying concepts. As Kahneman (2011) has written, “the automatic operations of System 1 generate surprisingly complex patterns of ideas, but only the slower System 2 can construct thoughts in an orderly series of steps”. Much of what the students had to say was not self-consistent and a number of students, on reflection or in response to a later prompt, changed their answer to a more scientifically reasonable one (see Table 3). Most students seemed to be relying on System I type thinking, rather than going back to first principles.

What became clear was that there was no single approach to solving this task and that the problems that arose in the students’ explanations combined in different ways to produce varied results. Some students (especially those who used personal heuristics) appeared to use reasoning that they could apply fairly consistently (if not correctly), but students who used a similar overarching heuristic often came to different conclusions. It may be that a few of these students' reasoning strategies might more closely align with the “theory” school of conceptual change. While their reasoning might be consistent, it was often based on a flawed model of phase change or an inability to decode the meaning of structural representations and technical terms. However, we believe that most students' ideas were fragmented and inconsistent; students often changed their responses during the course of the interview in a process more reflective of the conceptual change theories of diSessa (2008) where students' responses are constructed on the fly from a loosely woven tapestry of facts, skills, and concepts. What seems apparent from our findings is that, even after two years of chemistry courses, we have failed to help students make the crucial link between molecular-level structure and properties.

Questions and Implications for Teaching

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

This study seems to imply that students can take, and do well in, a “rigorous” set of chemistry courses without a thorough understanding of a core chemistry concept. All of these students made good grades and yet many reported that they had never thought about the questions asked in our interviews. That is, students appear to be quite accomplished and yet can harbor a range of problematic ideas that do not emerge under “normal conditions”. It should be reiterated here that all the students in this study had already been taught this information and passed examinations, including those developed by the chemistry community (ACS examinations) that are designed to encompass what students should know at the end of a given course. This problem brings up two major questions:

When are heuristics “good enough”? By necessity, the use of reasoning shortcuts increases as students move through the curriculum. Clearly students in organic chemistry cannot be expected to laboriously draw out each molecule and go through the long, drawn-out process of determining the three-dimensional structure, polarity, and types of IMFs for each question they are asked. Eventually, students must be able to “chunk” this material to avoid working memory overload, since they are also learning new material. However, if the answer to a question is “the boiling point is higher because of hydrogen bonding”, we must be certain that students mean hydrogen bonding between molecules, rather than within molecules. That is, reasoning shortcuts or heuristics must be based on a firm foundation, otherwise what appear to be reasonable answers to questions may hide fundamental problems.

What can be done to improve student understanding in chemistry so that when students do use shortcuts, they are appropriate and useful? Our findings make it clear that there is something wrong with our conventional approach to the development of these complex ideas. Each student constructed a unique approach to predicting structure–property relationships that emerged from the interaction of the factors discussed above. Although we found misconceptions that had previously been well-documented, the ways in which these ideas played out in the context of the question prompts were different and it is clear that addressing each problematic area separately will not be helpful for students in developing coherent conceptual frameworks. Our findings suggest that a scaffolded approach to the development of structure–property relationships, the development of progressions in which students are explicitly asked to connect their prior knowledge to new knowledge, and the explanation of how that knowledge will be used may help. For example, we have shown that students in a course designed in this way (Cooper & Klymkowsky, 2012) have an improved understanding of structure–property relationships (Cooper, Underwood, Hilley, & Klymkowsky, 2012) and further studies are being conducted to assess how long these improvements are retained.

What is also clear is that, as students go through organic chemistry, they tend to lose sight of the underlying principles that determine how substances interact. That is, while they have more content knowledge than students in general chemistry, they may be no more able to apply basic principles and, in some cases, the extra knowledge may actually impede their understanding. In addition to reconsidering how structure–property relationships are taught in general chemistry, we also recommend that the teaching of organic chemistry begin with a thorough, lengthy review of structure, interactions, and properties. While most organic texts begin this way, in our experience many instructors assume that an understanding of intermolecular forces and (for example) simple acid–base chemistry are prior knowledge and all that is needed is a brief reminder. Unfortunately, this is not the case. In general, students do not begin organic chemistry with a robust understanding of these ideas and therefore are doomed to “play catch-up”. Some students never do catch up and though they may emerge from the course with a database of memorized reactions, they are telling the truth when they inform the next generation of students that organic chemistry is all memorization. For them it can be no other way, since they do not have the tools to understand in a more meaningful way.

We also recommend that instructors return to these principles early and often, reinforcing the underlying concepts rather than expecting students to memorize large databases of reactions. Organic chemistry is a terminal course in chemistry for many students and is the last time many students will have the opportunity to develop important and worthwhile skills. Students must be asked to construct and explain their answers, so that their thinking can me made clearer, both to themselves and to their instructors. It is well documented, for example, that socially mediated learning provides opportunities for students to explain and construct understanding (Singer, Nielsen, & Schweingruber, 2012). Other approaches may involve explanatory writing (Greenbowe, Rudd, & Hand, 2007; Vázquez et al., 2012) and drawing to learn (Ainsworth, Prain, & Tytler, 2011), and the use of modeling and construction of models of appropriate systems (Schwarz et al., 2009). If students are never required to articulate their ideas, it is unlikely that they will have the opportunity to reconstruct them.

Limitations of this Study

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

In this study, we interviewed 17 students and each student provided us with a different combination of models, heuristics, and understanding of the meaning of both words and structures to answer our questions and construct explanations. We do not believe that we have uncovered every potential problem for students or described every student model, but we do think that we have presented a rich picture of the nature of the problem that faces us. We contend that it is not possible, nor is it necessary, to predict all the ways that students use their understandings to construct explanations for these phenomena. What is important is that instructors are aware of the extent of the problem and redesign both curricula and formative assessments to help students explicitly develop and connect these core ideas.

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information
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Note
  1. 1

    We will use misconceptions here because that is the term most prevalent in the chemistry education literature.

Supporting Information

  1. Top of page
  2. Abstract
  3. Introduction
  4. Background—Misconceptions, Conceptual Change, and Dual Processing
  5. Purpose and Significance of the Study
  6. Methods
  7. Findings
  8. Discussion
  9. Conclusions
  10. Questions and Implications for Teaching
  11. Limitations of this Study
  12. References
  13. Supporting Information

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