Difficulties Teaching Abstract Concepts in Secondary Chemistry Classroom
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Loraine P. Snead
Difficulties Teaching Abstract Concepts in Secondary Chemistry Classroom
Abstract Examining research surrounding the difficulties teaching abstract chemistry concepts to students in secondary school classrooms, suggests that the lack of comprehension and emerging misconceptions warrants new research. While the abstract concepts in chemistry are many, two are discussed in this paper: chemical bonding and atomic orbitals. Piaget (1958) introduces four stages of cognitive growth which determine the reasoning and mental development skills of which a child or adolescent is capable. While a large portion of development and capability is linked to gene inheritance, many secondary-school-aged children have not yet reached the capacity to understand abstract concepts without a concrete basis. Most researchers agree on the issues that abstraction presents, however, they differ on the most appropriate way to stimulate this development. Duschl and Hamilton (2011) introduce three frameworks, or learning progressions, which define how material is presented in an educational context. These learning progressions can be used to understand how students’ comprehension develop over time, and can help instructors create appropriate educational instruction and curricula for the classroom. In the face of critique on teaching abstract concepts in introductory science classes, Tsarpalis (1997) of the University of Ioannina in Greece, presents several convincing arguments about the origin of students’ misconceptions. He suggests that many students enter higher-level education with an incomplete or incorrect knowledge of chemistry concepts. In a five-year study, he provided different groups of students with a conventional lecture-based curriculum, and in each trial, the students performed poorly, likely due, he said, to incomplete secondary education (Tsarpalis, 1997). As a pre-requisite secondary course for students desiring a future in the sciences, the question is whether to teach the students adequate and correct theory in secondary school in order for them to be better prepared in college, or to forego teaching them abstract concepts at all. Sanchez Gomez et al. (2003), argue that current scientists are limited by their lack of understanding abstract knowledge, especially in the area of quantum mechanics. He goes on to infer that it is important that students learn quantum principles as soon as possible (Sanchez Gomez, 2003). Many other scientists mentioned in this review suggest that conceptual (as opposed to mathematical) approaches are necessary to teach students correct interpretations of quantum theories, an example of which is chemical bonding. While a large part of cognitive development and capability is linked to genes and maturity, many students can be taught abstract thinking through learning progressions using concrete and practical links. The link or model that is used should be based on helping students visualize and form conceptual image of the abstraction. Spectroscopy is an excellent tool to use to complete the understanding of chemical bonding and atomic orbitals. This review summarizes the research that supports the potential benefits of using spectroscopy to teach secondary school students chemical bonding is needed.
Introduction This paper briefly examines research surrounding the difficulties teaching abstract chemistry concepts in secondary classrooms and suggest that research into using spectroscopy to teach these concepts is one solution. The difficulties may be based on a lack of physical concrete visuals and/or appropriate pedagogical methods. Recent research in the area of visual thinking holds promise for helping students “see” the “unseen” (Barry, 1997) Concepts such as chemical bonding and electron arrangement L.Snead that have their underpinnings in quantum chemistry can be taught through spectroscopy. First, in order to address the abstract thinking issue, it is important to understand the cognitive research surrounding it. Jean Piaget, well-known child psychologist, postulates that there are four stages of cognitive growth: sensory-motor intelligence (from birth to age two), preoperational thought (from age two until eight), concrete-operations (from age eight to twelve) and formal reasoning, which begin during adolescence (Inhelder and Piaget, 1958). Piaget labeled the final stage of intellectual growth from concrete to abstract thinking the “formal operational stage” (Inhelder and Piaget, 1958). It is believed that only two-thirds of adults ever reach this state of abstract thinking. Moreover, this formal operational thought, or the ability to generate creative solutions for abstract issues, may not appear until age twenty or thirty (Healy, 2004). How, then, are instructors expected to teach undergraduate and secondary age students abstract science concepts? A large part of intellectual growth stems from inherited traits, but can this specific type of intellect be taught if the inherited links are weak or delayed in development? The future of science, indeed the future of our society, is contingent upon more students developing these capabilities earlier in their developmental cognitive abilities (National Commission on Excellence in Education, 1983). Americans can appreciate the urgency of this matter by examining the comparative international indicators of complex learning and applied knowledge published by the Organization for Economic Co-operation and Development (OECD) PISA program. The 2006 Program for International Student Assessment (PISA) focused on science literacy including an evaluation of students’ ability to interpret data, critique scientific evidence, and apply knowledge of scientific concepts to current topics such as DNA fingerprinting and biodiversity (Songer et al., 2009). On the 2006 test, 15- year old Americans performed poorly overall, ranking 29th out of 57 countries. Finland, Hong Kong, and Canada ranked first, second and third respectively. The major questions that guide this study, relate to how abstract thinking is defined in the scientific world, especially on the topics addressed in most high school chemistry classes. Why is abstract thinking important in understanding chemistry? Is abstract thinking developmental and if so, are high school students psychologically ready to think this way? Can a more practical and visual technique such as spectroscopy be used to teach conceptual quantum chemical principles in high school classrooms?
Abstract and Concrete Thinking Most cognitive psychologists define abstract thinking as characterized by the ability to use concepts and to make and understand generalizations. According to experts from the Brain Injury Association of New York State, abstract thinking involves the ability to think about ideas that are removed from the facts of the “here and now” and from specific examples of the things or concepts being thought about (Ylvisaker et al., 2006). In essence, it is what the mind is able to form when stimulated in the absence of a concrete subject. The mid-1990s provide better insight on the history of abstract thinking in educational psychology. As previously mentioned, Piaget suggested that a child’s cognitive abilities or intellect proceed through four distinct stages: sensory-motor, pre- operational, concrete operational, and formal operational adolescence (Inhelder and Piaget, 1958). Piaget further noted that development precedes learning and that the developmental stages are discrete. His main views in cognitive intellect suggested that non-developmental stage learning could not take place unless the child was on the verge of moving to the next stage. Currently, however, critics argue that Piaget underestimated 2 L.Snead children’s abilities (Lawson, 1985). Children are more competent than Piaget thought and, more importantly, their skills develop individually on different tasks – the progress of one student cannot be used to track the development of another the same age. In addition, their formal educational experiences have changed, especially as teachers become better trained in using various researched methodologies to improve higher order thinking. Higher order thinking in this context is understood to be when students can take information and ideas from one context and infer their meaning and implications in another. The pedagogy used in the classroom can have a strong influence on the pace of development (Byrnes, 1988;Gelman, et al., 1983; Overton, 1984). Children in the pre- formal operational stage can form concepts that are independent of physical reality. As Gelman and Baillergeon assert, “the experimental evidence available today no longer supports the hypothesis of a major qualitative shift from preoperational to formal operational thought.” In other cognitive research, Pribyl (1995) documented that young children in groups of three to five year-olds are able to think in abstract terms, making sense of their world through creating intuitive models. These scientists concluded that young children are able to engage in experimentation to develop their ideas. There are many other views on the stimuli behind progressing through the four stages. While many think maturation is a pre-requisite for abstract thinking, there are many alternate beliefs. Some view an appropriately stimulating physical and social environment will provide the necessary neurological development (Lawson, 1985). Again, it is possible for the pedagogy used in the classroom to enable the transition from concrete to abstract thinking. The following example illustrates the difference between concrete and abstract thinking. A concrete thinking adolescent can recognize that the organization of an essay in English class needs a thesis statement and several points or arguments that support the thesis statement. An abstract thinker can recognize that this strategy in an English class essay is the same as using the idea of a thesis statement as the purpose and the arguments as evidence in a Chemistry class laboratory report. In a review of research on formal reasoning and science teaching, Lawson (1985) argues “biological maturation during late childhood or early adolescence may not play a significant role in the development of formal reasoning.” With respect to Piaget’s groundbreaking work in cognitive development, it must be noted that the aforementioned formal operational thinking does not necessarily occur in adolescence and as mentioned earlier, it may be that it doesn’t appear until well into adulthood. Research on science learning appears to be moving away from a focus on general principles of learning science to a focus on the psychological, social, and cultural factors that influence the development of domain specific science knowledge. According to Duschl and Hamilton (2011) there are three frameworks in the current research on the learning of science: theory and research on core knowledge, learning progressions, and domain-specific and domain-general learning frameworks. Duschl and Hamilton also noted that these frameworks overlap: learning progressions (LPs) are embedded into the domain-specific and the core knowledge frameworks. Learning progressions can be seen as tracking the progress of how students’ understandings of and abilities to use core ideas grow and become more sophisticated over time. A key component of learning progressions is also embedded in the notion of instruction-assisted development like that described in the learning pathway on matter and the atomic molecular theory (Smith et al. 1985). Assisted development can be utilized when learning is stalled, because of the need for abstract reasoning even in elementary age children. Here, thoughtful and informed 3 L.Snead curriculum designs and effective remediation on the part of teachers can move learners forward. (Leher et al. 2008; Metz, 2008). Recently, Duschl and Hamilton (2011) stated that there are several areas of science learning that haven’t been researched fully and need more investigation. The future research on science learning and teaching needs to focus more on learning in context. Research is needed on developmental trajectories/progressions that examine learning and reasoning. Also, research is needed to develop a better understanding of whether (and how) instruction should change with children’s development. In addition, their findings conclude that research on new curriculum materials is a critical area. Teaching abstract concepts to concrete thinkers can theoretically be accelerated, but only through purposeful planned interactions between the concrete thinker and a more mature and well-trained adult. High school science teachers can teach students abstract chemistry, such as quantum mechanics, using a combination of learning methods and in many cases using visual and spatial representations (Schwartz et al., 2006).
Common orbital concept in high school textbooks In most high school chemistry textbooks, the concept of orbitals is taught as a precursor, or as a necessary mean to an end. The end being that “the atoms of each element have a unique arrangement of electrons” (Buthelezi et al., 2008). The usual treatise by the authors in efforts to arrive at the electron configuration of atoms starts with Light and Quantized Energy and then Quantum Theory and the Atom. Buthelezi et al. (2008) depict an atomic orbital as a “density map” representing the probability of finding an electron in a region around the nucleus, similar to Figure 1.
Figure 1. Electron cloud model depicts a density map of electrons in an atom. (Time Line, http://hi.fi.tripod.com/timeline/timeline.htm)
There is also a short discussion about Schrödinger’s wave equation in the same textbook sections (Buthelezi et al., 2008). In summary, the treatise states that the equation treats the hydrogen atom’s electron as a wave, but the equation is too complex to be considered in the text.
Alternative Conceptions (misconceptions) in Chemistry
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According to a research review provided by Tsaparlis (1997) students start undergraduate quantum chemistry courses with either incomplete knowledge or alternative conceptions (misconceptions) about quantum-chemical concepts. He attributed these conceptual difficulties to ill-informed secondary teachers, poorly written textbooks and ineffective teaching pedagogy. Tsaparlis suggests that because of the misconceptions that undergraduate students bring to college, lecturers are against the use of certain concepts being taught in high school, based on the limited explanations and predictions found in high school chemistry textbooks. He concludes that the imprecise and elementary pictorial coverage of quantum concepts is the primary cause of students’ misconceptions. This is not a solitary view, even to the extent of critics commenting that atomic orbitals should not be taught at all, because orbitals simply don’t exist. One scientist speaks for many critical perspectives, arguing that there is no “right” way or best way to depict orbitals, that orbitals are constructs, and at best unproven theory (Ogilvie, 1990). This belief, among many other statements made by Ogilvie was strongly criticized by Linus Pauling (Pauling, 1992). While Pauling agreed that orbitals should not be taught in introductory chemistry courses he maintained that they could be represented through quantum mechanical expressions. There have been several other theorists expounding against teaching orbitals and related quantum mechanical concepts in introductory courses (Bent, 1984; Berry, 1996; Gillespie, 1991; Hawkes, 1992). They believe that these concepts are highly abstract and beyond the understanding of most students. Tsaparlis defends this belief, and supports it by tracking undergraduate students in a required fourth semester quantum chemistry course of the four-year chemistry degree program at the University of Ioannina (Greece). Tsaparlis taught the course in a traditional university lecture-based class. He administered a cumulative final exam to the students in the form of mostly free-response questions with a limited number of multiple- choice questions. All of the questions on the exam were deemed typical and suitable for an undergraduate quantum chemistry course by several professors at the University. The results of 506 students’ assessments show that only 41.9% of the students passed with at least a 45.0% minimum grade. According to Tsaparlis their lack of success points to “misconceptions, errors, and lack of knowledge that may prevail among future secondary school chemistry teachers”. He further asserts that these deeply held misconceptions couldn’t be easily corrected by later and more advanced instruction. One revealing misconception came from a question about atomic-orbital shapes. The question referred to four representations of atomic orbitals from Tsaparlis’ paper, shown below in Figure 2. The actual question is written below the figures, asking: what does each of the figures represent for a hydrogen-like pz orbital? Less than half of the students answered correctly. Tsaparlis was particularly disappointed that one of the statistically lowest performance (N=52, M=29.4% with SD=36.5%) was for descriptions of (a) and (d). He attributes the incorrect descriptions of Figure 2a to students’ holding on to previously learned instruction that the pz orbital has the shape of a “figure-eight.” Tsaparlis uses the data accumulated from this study to further substantiate his claim that incomplete and/or incorrect previous instruction may develop misconceptions that are very hard to correct by later, advanced instruction. Figure 2(a) is a cross-section of the graph of (, ) for the pz atomic orbital, not the shape of a pz orbital.
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Figure 2. The actual question about atomic-orbital shapes in two examinations: What does each one of the representations, (a), (b) and (c) represent for a hydrogenic pz orbital? What does (d) represent for the 2py orbital? (Tsaparlis, 1997)
More recently, Talanquer, associate chemistry professor at the University of Arizona reasoned that it is “common sense” that interferes with students’ scientific learning. He lists the numerous misconceptions students bring to chemistry courses, including the mole concept, changes of state, chemical reactions and, atomic and molecular structure (Talanquer, 2002). Talanquer develops “eight patterns of reasoning”, one of which suggests that there is a one-to-one correlation between models or images that represent abstract concepts to the concrete model or image. Bliss supports Talanquer,
6 L.Snead through a twenty-year study on reasoning and thinking in adolescents in the United Kingdom. The study aimed to determine how students reason in the everyday physical world (Bliss, 2008). Initially, her research was concerned with the difficulties students experienced in reasoning about concepts involving force and motion. The results showed that the students were using everyday knowledge to explain and reason about these physical areas. It was clear that instead of the students using concepts and ideas that they learned in school to reason about force and motion, they consistently fell back on their “common sense.” learned from the physical world. Bliss further proposed that an important part of human reasoning uses concrete physical schemes to explain the physical world. It appears, then, that Talanquer’s characterization has merit. Following his logic, it is possible that common sense is what causes students to misunderstand the various abstract chemistry concepts such as chemical bonding.
Chemical Bonding Chemical bonding is commonly defined as a net attractive force that joins two or more atoms (Buthelezi et al., 2008). It is better described as an attraction that occurs when one or more electrons are simultaneously attracted to two nuclei. The subsequent compound made is stable when the total energy of the combination of atoms has lower energy than the separated atoms. This minimum energy exists at a specific equilibrium length, or inter-nuclear distance between the atoms and that distance is called the bond length. A bond (or attraction) between the atoms is not static, and is often introduced in the classroom in comparison to a spring that vibrates about its equilibrium position. The molecules are constantly vibrating, which involves a displacement of the atoms from their equilibrium positions (Engel, 2006). The bond energy is a direct measure of the strength of this bond. The value of bond energy of electrons in free atoms is calculated by wave functions (i.e., quantum mechanical methods), but it is difficult to determine the energy of bonds in molecules this way because the electrons and nucleus energy changes during hybridization (Korablev et al., 2006). The concept of chemical bonding is one of the most important topics in general chemistry because it is related to so many other fundamental concepts that make up the true nature of chemistry, for example, chemical reactions. The teaching and learning of chemical bonding should be at the forefront of any secondary and undergraduate general chemistry classroom. Chemical bonding is also one of the more abstract concepts that, if not taught carefully, can help to proliferate the deeply imbedded misconceptions of students. In fact, while researching this topic of teaching and learning chemical bonding, Nahum’s group at the Weizmann Institute of Science found that there are many different views among prominent scientists on the definition of chemical bonding and how it should be taught (Nahum et al., 2010). One view shared by most scientists, however, is that bonding is complex, and involves several factors. It is the very nature of a chemical bond, whether covalent, ionic, or hydrogen, that relates directly to atomic and molecular orbitals. Therefore, if chemical bonding is one of the more important concepts to learn, but one of the more difficult concepts to teach, then it begs the question: when and how should orbitals be taught? Should orbitals be taught in secondary chemistry classes? If the majority of secondary chemistry teachers use textbooks as the main (sometimes the only) source of information, chemistry teachers will become instructors in the history of scientific development and discovery, for better or worse (Chamizo, 2007). Realizing that there has been substantial debate on whether or not orbitals should be 7 L.Snead taught in high school, the assertion is obvious; if we continue to teach orbitals and chemical bonding as introduced by Pauling in 1922, these abstract and common-sense- reasoned concepts will have to be replaced later, or unlearned in college.
Quantum Mechanics According to Sanchez Gomez et al. (2003), if we are to thoroughly understand the structure of matter, given the current state of knowledge we will need to use quantum chemistry. Sanchez Gomez examined the future of learning chemistry and decided that the old models proposed by the important historical figures such as G.N Lewis and Linus Pauling, who introduced Lewis dot structures, Valence Shell Electron Pair Repulsion (VSEPR) theory, and atomic orbital hybridization rules, are declining in terms of their efficacy to explain current research. While quantum chemistry has been around for close to a century, Sanchez Gomez argues that it has certain limitations for chemists. Most would say that it is because chemists are concerned with physical reactions and making various iterations of experimental methods and procedures (Sanchez Gomez, et al., 2003). According to Sanchez Gomez, the true reason that chemists don’t embrace quantum mechanics more is that they only have a superficial knowledge of how quantum mechanics can be applied to chemistry problems. Moreover, using the old models to depict molecular structure has limitation. He further states that during the last twenty years advances in modern research fields such as the chemistry of plasmas and flames, higher atmosphere and interstellar space challenge the explanatory power of old models. There is reason to research new models to use when teaching molecular structure. There is plenty of research describing methods to teach quantum mechanics to undergraduate students and/or high school students (Deratzou et al., 2000; Fanaro, 2009; Gomez-Herrero, 1999; Thaller, 2006; Zollman, 2001). It appears that the more successful methods involve using some kind of visualization and that the emphasis is on conceptual knowledge as opposed to a mathematical approach (Fanaro, 2009; Neto et al. 2007; Robblee, 1999). Zollman (2001) concludes that a good interpretation of the basic concepts of quantum theory is what is important to learn in introductory chemistry classes. Deratzou (2006) reasoned that high school students learning about chemical bonding and molecular structure improved significantly through visualization and imagery. She concluded “students who learned the chemistry concepts more effectively were better at visualizing structures and using molecular models to enhance their knowledge”. She goes on to infer that visualization of molecular models provides a “scaffold” between abstract and practical knowledge. In addition, her results show that students who were not initially visual learners demonstrated spatial perception after being trained in visualization.
Spectroscopy Whereas quantum mechanics is a theoretical subject, its applications can be seen in a more experimental and visual subject, namely spectroscopy. Spectroscopy is associated with the absorption, emission, or scattering of electromagnetic radiation by atoms or molecules. In absorption spectroscopy, a molecule absorbs the energy of incident radiation and undergoes a transition from a state of lower energy to a state of higher energy. An emission spectrum is produced when radiation is emitted from a higher to a lower energy state. In both techniques, the change in the energy, E whether
8 L.Snead absorbed or emitted is proportional to h (h= Planck’s constant and = frequency). The energy of a molecule can change as a result of molecular rotations and vibrations and can be imaged on a graph called a spectrum. Hollas (2004) in Modern Spectroscopy describes the basic molecular spectroscopic techniques as rotational, vibrational, and electronic. Since the various forms of spectroscopy are among the most powerful tools that chemists use to determine atomic and molecular characteristics, it can be used to teach bonding and atomic orbitals. Vibrational spectra are ordinarily measured by two different techniques: infrared (IR) and Raman spectroscopy. The transitions between the set of energy levels associated with molecular vibrations can give rise to absorptions in the IR part of the electromagnetic spectrum. Changes in vibrational energy are accompanied by simultaneous changes in rotational energy, but rotational energies are much smaller (Atkins et al., 2002). Two features of vibrational spectroscopy that enable it to be useful in discussions of bonding are 1) vibrational frequency of a molecule differs depending on the identity of the atoms and 2) a particular vibrational mode in a molecule has only one major characteristic frequency of any appreciable intensity (Engel, 2005). These properties generate characteristic frequencies or what is commonly known as group frequencies in IR spectroscopy. Therefore, the energy of a molecular vibration depends on the internuclear distance of the atoms that constitute a chemical bond (Campaan et al., 1994). In rotational spectroscopy there are sets of energy levels associated with the overall rotation of molecules; transitions between these levels give rise to spectra that typically appear in the microwave section of the electromagnetic spectrum. In order to predict which energy states are allowed, there are selection rules. Selection rules express the allowed transitions in terms of quantum numbers (not discussed in this review). There are also “gross selection rules” which specifies the general features a molecule must have if it is to undergo a change in energy states. An example of a gross selection rule used in when studying rotational spectroscopy is that in order for there to be transitions between the rotational energy states, the molecule must contain a permanent dipole moment (Atkins et al. 2002). Last, electronic spectroscopy involves energy that causes electrons to transition from one level to another while simultaneously promoting both vibrational and rotational transitions. If the analyte is a liquid, the absorption bands are too broad to decipher vibrational and rotational information (Harris et al., 1989). However, at low temperatures and in the gas phase vibrational structure can be resolved. The energy transitions are induced by visible and ultraviolet radiation. Electronic spectra are sometimes used in high school classrooms to show that the emission spectra of certain elements consist of several individual lines of color corresponding to visible radiation frequencies (Buthelezi et al., 2008). Figure 3 below, shows a potential energy curve of electronic, vibrations and rotations of a diatomic molecule. The electronic transitions are the vertical lines; vibrational transitions occur between different vibrational levels of the same electronic state; rotational transitions occur between rotational levels of the same vibrational state.
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Figure 3: Potential curve of electronic, vibrational and rotational transitions as a function of internuclear separation. (http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html)
Conclusion To improve understanding of abstract chemistry concepts, such as chemical bonding, new models that are both practical and concrete, should be researched. The key bonding concepts, such as orbitals, electron repulsions, internuclear attractions, and Coulomb’s Law, are all non-tangible (nor visual) theories, and therefore difficult for students to fully understand. As Sánchez Gómez et al., (2003) discussed, the most advanced models available to chemists for understanding the structure of matter are derived from quantum chemistry. Because spectroscopy is considered to be an application of quantum chemistry, it may provide the needed “link” from concrete to abstract thinking. Raman spectroscopy is one example of a tool that illustrates the rotational energies of simple gases, like O2 and N2 in the ground state. These Raman spectra can be used to teach how molecular internuclear distances within gas molecules change depending on atom identity (Campaan et al., 1994). The visual changes in the frequencies of the different molecules can be observed readily on the spectra, giving students a concrete and visual representation of a chemical bond. Future research on the application of abstract chemistry concepts will help to shape the methodology used to teach secondary school students abstract concepts. As such, it is imperative that more research is conducted in order to improve methods of chemistry instruction, especially at the secondary level.
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