Research: Science and Education edited by
Chemical Education Research
Diane M. Bunce
Ionization Energy: Implications of Preservice Teachers’ Conceptions
The Catholic University of America Washington, DC 20064
Melanie M. Cooper Clemson University Clemson, SC 29634
Kim Chwee Daniel Tan* Natural Sciences and Science Education, National Institute of Education, Singapore 637616; *
[email protected] Keith S. Taber Faculty of Education, University of Cambridge, Cambridge, CB2 8PQ, United Kingdom
The topic of ionization energy is introduced in the A-level (grades 11 and 12, ages 16–19 years) chemistry courses in countries such as Singapore and the United Kingdom. Understanding the concepts involved in ionization energy is important because these concepts are also found in other topics such as atomic structure, bonding, periodic trends, and energetics of reactions (1). These concepts, similar to many other concepts in chemistry, are difficult to understand as they are abstract, draw on a range of scientific models (2), and involve explanations of interactions between particles at the sub-microscopic level (3). These explanations draw upon factors such as the effects of nuclear charge, electron–nucleus separation, “shielding electrons” in shells “inside” the outer shell, electrons in the same shell, net charge on remainder of atom or ion as it is ionized, type of orbital occupied by the electron, and whether there is another electron in the same orbital (4). Students attempt to make sense of what they are being taught based on their prior knowledge (5) and if they cannot make any links to the new concepts taught, they may “bend” what is taught to fit somewhere, thus giving rise to alternative conceptions (6). Studies have shown that A-level students based their explanations of the magnitude of ionization energy on the octet rule, or full-shell framework, and “conservation of force” conception and did not or could not apply basic electrostatic principles that they learned in physics to explain the interactions between the nucleus and electrons in an atom (1, 7–10). The octet rule and full-shell framework considers the attainment of “full shells” or octets of electrons as a driving force for chemical change, and so students use these as explanatory principles suggesting that changes occur because atoms “want” to fill their shells or obtain a stable octet of electrons in the valence shell (7). In addition, many students also used the acquisition of full or half-filled subshells as explanatory principles in a similar way (10). The conservation of force conception considers the force attracting electrons to a nucleus to be a fixed quantity depending (only) upon nuclear charge and being distributed among the electrons present in an atom or ion. Here there is no effective differentiation between nuclear charge (constant for a particular nucleus) and the force acting on electrons owing to the nucleus (an interaction depending on separation as well as charge magnitude); the force from the nucleus is said to be “shared-out” among electrons (8). Students’ thinking often demonstrated relation-based reasoning (11) or heuristic reasoning (12), reducing a complex situation to a single linear cause-and-effect to explain the trend of ionization energies across period 3 elements (10).
Many common alternative conceptions are considered to have their origins outside the classroom (13). Since students only encounter the concepts involved in ionization in formal chemistry classes, it seems likely that alternative conceptions that develop here derive largely either from (i) interpreting teaching in terms of existing intuitive ideas (14–16) or (ii) in some cases from teaching that is based upon, or implies, misconceptions (17). So it is possible that teachers can also have similar alternative conceptions and may unwittingly transmit their alternative conceptions to their students and think that there is nothing wrong with their students’ understanding (18, 19). Indeed, studies have shown that preservice teachers have alternative conceptions similar to that of students (20), for example, in the areas of chemical equilibrium (21), redox reactions (22), and inorganic qualitative analysis (23). Thus, it is important to determine teachers’ understanding of difficult science concepts to help them address any difficulty or alternative conceptions that they may have as how they think will affect the way they teach these concepts to their students (24). Purpose This study sought to determine the extent of graduate preservice teachers’ understanding and alternative conceptions of the factors influencing ionization energy and of the trend of ionization energies across different elements in the periodic table at the A-level. A two-tier multiple choice diagnostic instrument, the Ionization Energy Diagnostic Instrument (IEDI) (10) was used in the study. Instrument Two-tier multiple-choice tests use questions that have two parts. Generally the first part tests knowledge and the second part underlying understanding (25, 26). A question is only considered correctly answered when the correct responses are chosen for both the “what” and “why” aspects. For example, in the IEDI, the first question requires respondents to both select the option that an electron removed from an atom would recombine with it and to select the option explaining this in terms of the attraction of opposite charges. This type of instrument is developed through a process that starts from a comparison of curriculum knowledge and free responses provided by students in interviews to suggest potential foci for questions and then refines test questions found to have
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 5 May 2009 • Journal of Chemical Education
623
Research: Science and Education Table 1. Preservice Teachers’ and A-Level Students’ Performance on the IEDI Test Statistic No. of participants No. of questions Mean (standard deviation) Median Mode Minimum–Maximum
Preservice Teachers
A-Level Students
237
979
10
10
3.59 (2.37)
2.91 (1.91)
3.00
3.00
3
2
0–9
0–9
diagnostic value (25). The development and validation of the IEDI has been previously reported (27). The IEDI has previously been used to investigate students’ understanding of the ionization energy topic in Singapore (10) and in a cross-national study involving students from four continents (28). The complete IEDI as well as the learning outcomes related to A-level students’ understanding of ionization energy are available in the online material and in JCE QBank. Method and Procedures The IEDI was administered to 237 graduate preservice chemistry teachers who enrolled in a chemistry pedagogy course over the period 2003 to 2006 in a teacher education institution in Singapore. All preservice teachers who took part in the study have elected chemistry as their first (main) teaching subject. It is only such preservice teachers who can be assigned to A-level institutions to teach A-level chemistry. The majority of these graduates had degrees in chemistry, while the rest had degrees in biochemistry, materials science, materials engineering, or chemical engineering. The participants were asked to read up on the topic of ionization energy as taught at A-level a few days prior to the test. During the test, they were instructed to answer the questions in the IEDI without any discussion. There was no time restriction for the test, and on the average, the preservice teachers took 20–30 minutes to complete the IEDI. The participants’ answer sheets were marked using an optical mark reader, and their results were analyzed using SPSS Release 14 (29); the focus was on descriptive statistics. As is the usual procedure for two-tier multiple choice tests, each question was considered to be correctly answered only if a participant correctly responded to both parts of the question (30, 31). Results Some test statistics from the IEDI test are given in Table 1. The results of A-level students’ performance on the IEDI from a previous study (10) were included as a comparison. Overall, the preservice teachers did not fare very well on the IEDI with 66% of them getting four or fewer questions correct out of 10. That is, two-thirds of these graduate trainees were only able to correctly answer a minority of the questions relating to an area of chemistry they would be expected to teach.
624
Table 2. Percentage of Preservice Chemistry Teachers Selecting Each Response Combination for Each Question in the IEDI (n = 237) Reason Option
Question
Content Option
(1)
(2)
(3)
(4)
(5)
1
A B C
5.5 0.4 0
43.9 3.0 0
0.8 40.1 0.4
– – –
– – –
50.2 43.5 0.4
2
A B C
7.6 29.1 0.8
0 0.4 0
54.0 3.0 0
– – –
– – –
61.6 32.5 0.8
3
A B C
27.4 4.2 0.4
0.4 1.7 0
0 1.7 0.4
0.8 55.7 0
– – –
28.7 63.3 0.8
4
A B C D
27.0 0 3.8 0
18.6 0 0 0
41.4 0 0 0
0.8 0.4 0 0
– – – –
87.8 0.4 3.8 0
5
A B C
1.7 19.0 0
0.8 11.8 0
0.8 48.5 0
7.6 2.5 0
2.1 0 0
13.1 81.9 0
6
A B C
18.1 0 0.4
50.6 3.0 0
1.3 6.3 0
7.2 0.4 0
1.3 3.0 0
78.5 12.7 0.4
7
A B C
0.8 0.8 0
0.8 8.9 0
12.2 3.0 0
11.4 5.1 0
1.7 46.8 0
27.0 64.6 0
8
A B C
0.8 2.5 0
5.5 37.1 0
2.1 0.8 0
2.5 36.3 0
– – –
11.0 76.8 0
9
A B C
1.7 1.3 0
1.7 0 0
41.4 2.5 0.4
0.8 5.5 0.4
33.8 0.8 0
79.3 10.1 0.8
10
A B C
15.2 5.5 0
2.1 0.8 0
2.1 48.9 0
9.7 4.6 0
– – –
29.1 59.9 0
Total
Note: Figure in bold indicates the correct answer. Figure in italics indicate a major alternative conception (>10%).
The percentage of the preservice teachers selecting each response combination for each question in the IEDI is presented in Table 2. The results for a question did not add up to 100% where there were preservice teachers who did not select a response to both parts of the question, selected an answer combination that was beyond the options given in the question (for example, choosing option “C5” when there are only two options, A and B, in the first-tier or four options, 1 to 4, in the second-tier), or selected more than one answer combination. Incorrect response combinations were considered significant if they were selected by at least 10% of the preservice teacher sample (32). Table 3 summarizes the significant common alternative conceptions under the headings of “Octet Rule Framework”, “Stable Fully Filled or Half-Filled Subshells”, “Conservation of Force Thinking”, and “Relation-Based Reasoning”. Cross-tabulations of the preservice teachers’ options related to the alternative conceptions are given in Table 4.
Journal of Chemical Education • Vol. 86 No. 5 May 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
Research: Science and Education Table 3. Alternative Conceptions Indicated by Common Response Combinations Selected by Preservice Teachers and A-Level Students Choice Combination
Alternative Conception
Preservice A-Level Teacher Students (%, n = 237) (%, n = 979)
Octet Rule Framework The sodium ion will not recombine with an electron to reform the sodium atom, as its stable octet configuration would be disrupted.
Q1 (A2)
44
44
The Na(g) atom is a less stable system than the Na+(g) and a free electron because the Na+(g) has a stable octet configuration.
Q3 (B4)
56
64
The second ionization energy of sodium is higher than its first because the stable octet would be disrupted.
Q4 (A1)
27
16
The first ionization energy of sodium is less than that of magnesium because sodium will achieve a stable octet configuration if an electron is removed.
Q5 (B2)
12
9
The first ionization energy of sodium is less than that of magnesium because magnesium has a fully filled 3s subshell.
Q5 (B1)
19
13
The first ionization energy of magnesium is greater than that of aluminium because removal of an electron will disrupt the stable completely-filled 3s orbital of magnesium.
Q6 (A1)
18
6
The first ionization energy of silicon is less than that of phosphorus because the 3p subshell of phosphorus is half-filled.
Q8 (B2)
37
25
The first ionization energy of phosphorus is greater than that of sulfur because the 3p subshell of phosphorus is half-filled, hence it is stable.
Q9 (A3)
41
20
Q10 (A1)
15
7
When an electron is removed from the sodium atom, the attraction of the nucleus for the “lost” electron will be redistributed among the remaining electrons in the sodium ion.
Q2 (A3)
54
50
The second ionization energy of sodium is greater than its first ionization energy because the same number of protons in the Na+ ion attracts one less electron, so the attraction for the remaining electrons is stronger.
Q4 (A2)
19
18
The first ionization energy of magnesium is greater than that of aluminium because the 3p electron of aluminium is further from the nucleus compared to the 3s electrons of magnesium.
Q6 (A2)
51
48
The first ionization energy of sodium is greater than that of aluminium because the 3p electron of aluminium is further away from the nucleus compared to the 3s electron of sodium.
Q7 (A4)
11
21
The first ionization energy of sodium is greater than that of aluminium because the 3p electron of aluminium experiences greater shielding from the nucleus compared to the 3s electron of sodium.
Q7 (A3)
12
24
Stable Fully Filled or Half-Filled Subshells
The first ionization energy of silicon is greater than that of sulfur because sulfur will have its 3p orbitals half-filled if an electron is removed. Conservation of Force Thinking
Relation-Based Reasoning
Table 4. Cross-Tabulations of Options Indicating Similar Alternative Conceptions Alternative Conception Octet rule framework
Options Cross-Tabulated
Preservice Teacher (%, n = 237)
Q1 (A2) & Q3 (B4) Q1 (A2), Q3 (B4) & Q4 (A1)
33 9
Stable fully filled subshells – magnesium as the common atom in the questions
Q5 (B1), Q6 (A1)
7
Stable half-filled subshells – phosphorus as the common atom in the questions
Q8 (B2) & Q9 (A3)
27
Conservation of force thinking
Q2 (A3) & Q4 (A2)
16
Relation-based reasoning – the more electrons an atom has, the further away are the valence electrons from the nucleus
Q6 (A2) & Q7 (A4)
8
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 5 May 2009 • Journal of Chemical Education
625
Research: Science and Education
Octet Rule Framework
Conservation of Force Thinking
A number of popular response combinations suggest that preservice teachers consider the attainment of a stable octet or noble gas configuration as an appropriate explanation for the phenomena. Many of the preservice teachers (44%) selected the response combination (Q1, A2) that the sodium ion would not recombine with an electron to reform the sodium atom, and that this was because the sodium ion had already achieved a noble gas configuration, so gaining an electron would cause the ion to lose its stability. A majority (56%) of the preservice teachers selected the response combination (Q3, B4) that a “sodium ion and a free electron” system was more stable than the sodium atom, and this was because the outermost shell of the ion had achieved a stable octet or noble gas configuration. Just over a quarter (27%) used the same rationale (Q4, A1) to explain why the second ionization energy of sodium was greater than its first ionization energy. Cross-tabulation of the response combinations (Table 4) indicated that 33% of the preservice teachers chose the stable octet or noble gas configuration response combination in questions 1 and 3. However, only 9% of the preservice teachers consistently chose the stable octet or noble gas configuration in questions 1, 3, and 4. As the diagnostic instrument only allows one response combination per question, where a respondent holds several alternative conceptions that are reflected in response options for a single question, their response will only reflect the conception that seemed most salient or relevant (see the Discussion section). About 12% of the preservice teachers selected a response option in Q5 (B2) that indirectly applied the octet rule framework to explain why the first ionization energy of sodium was less than that of magnesium: the sodium atom would achieve a stable octet configuration if an electron was removed, so it was easy to remove the electron.
A majority of the preservice teachers (54%) selected a response to question 2 (A3) based on the alternative conception of nuclear attraction being redistributed among the remaining 10 electrons when an atom of sodium loses an electron because the number of protons was the same but there was one less electron to attract. About 19% of the respondents selected the response using this same “conservation of force” thinking in question 4 (A2) to justify why the second ionization energy of sodium was greater than its first ionization energy: the same number of protons in the Na+ ion attracted one less electron, so the attraction for the remaining electrons was stronger. Cross-tabulation showed that 16% of the preservice teachers consistently chose the “conservation of force” option in questions 2 and 4.
Stable Fully Filled or Half-Filled Subshells Preservice teachers commonly selected response combinations to five of the questions that used the perceived stability of full or half-filled subshells as an explanation for the trend of ionization energies across several elements in period 3. Just under a fifth of respondents (19%, 18%) selected responses on questions 5 (B1) and 6 (A1), respectively, that used the notion of full subshells to justify judgments of relative magnitude of first ionization energies (that of sodium being less than that of magnesium and that of magnesium being greater than that of aluminum). However, only 7% of the preservice teachers consistently chose the “stable full subshell” option in both questions. For questions 8 and 9, 37% and 41%, respectively, of the respondents selected the option offering the notion of half-filled subshells to explain why the first ionization energy of phosphorus was greater than that of silicon (Q8, B2) and sulfur (Q9, A3). Cross-tabulation showed that 27% of the preservice teachers consistently chose the “stable half-filled subshell” option in questions 8 and 9. On question 10, a smaller proportion (15%) selected the response option that offered this principle as an explanation for the first ionization energy of silicon being greater than that of sulfur (response combination A1).
626
Relation-Based Reasoning A number of the common incorrect response combinations reflect reasoning based on factors that are in principle relevant, but that ignore the dominant relevant factor. About half (51%), and a tenth (11%), of the preservice teachers in the sample selected response combinations arguing that the first ionization energies of magnesium and sodium, respectively, were greater than that of aluminum because the 3p electron of aluminum was further away from the nucleus than the 3s electron(s) of magnesium (Q6, A2) and sodium (Q7, A4), respectively: responses inconsistent with the decrease in atomic radii across a period (which depends upon increasing nuclear charge as well as the increasing number of electrons in a shell). Cross-tabulation indicated that 8% of the preservice teachers were consistent in their choice of the option. About 12% of the preservice teachers selected the option (A3) in question 7 that sodium had a higher first ionization energy than aluminum because the 3p electron of aluminum experienced greater shielding than the 3s electron of sodium. Although the “reason” is, in itself, correct, the first ionization energy of sodium is actually lower than that of aluminum because the increase in nuclear charge of aluminum compared to sodium is a more significant factor. Discussion Understanding patterns in ionization energy is part of the curriculum in high school level courses such as the A-level course, and in tertiary chemistry, but this topic has been found to be problematic for many learners (1, 8). A full understanding of this topic requires knowledge of, and an ability to apply and coordinate, a range of concepts and principles: nuclear charge, the distance of an electron to be removed from the atomic nucleus, the quantity of shielding of that electron from the nuclear charge by the inner shell electrons, and the type of orbital that the electron occupies. Previous research developed a two-tier multiple-choice instrument to explore student understanding of the topic of ionization energies (27). When the instrument was used to survey A-level students in Singapore it was found that they demonstrated a variety of common alternative conceptions of the topic (4). Students at this level were found to often draw upon apparently intuitive ideas about the desirability of full shells or other particular
Journal of Chemical Education • Vol. 86 No. 5 May 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
Research: Science and Education
configurations and the sharing-out of nuclear force, rather than the basic electrostatic principles that represent target knowledge in the curriculum (15, 16). It was also found that where predictions about the relative magnitude of ionization energy needed to coordinate several competing factors, many students would commonly select responses that ignored the dominant factor. Comparing Preservice Teachers to A-Level Students Compared to the A-level students, the graduate preservice teachers who completed the test instrument in this study would be expected to have undertaken further relevant learning during their degrees and to be more familiar with, as well as more experienced in applying, the relevant concepts and principles. They would also explore some relevant topics in greater detail, for example learning about the penetration of outer shell electrons and the quantum-mechanical basis of electron spin. This might lead to the expectation that graduate preservice teachers would score higher on the IEDI and that alternative conceptions would be less common among this population. The mean score among the sample of preservice teachers was higher than among the sample of A-level students (Table 1), although the difference was modest. The proportion of A-level students selecting the response options that we have identified as indicating common alternative conceptions among the preservice teachers are shown in Table 3. Some statements reflecting alternative conceptions are chosen by a smaller proportion of the preservice teachers than the A-level students. However, in other cases such options are as, or indeed more, popular with the preservice teachers. In some cases the popularity of particular incorrect response combinations is very similar at the two educational levels, whereas in other cases the differences are more pronounced. Further research to explore and explain these patterns may prove informative, especially where response combinations indicating alternative conceptions are more popular among the graduate preservice teachers. The significance of the present study, however, is that while there are differences between the response profiles of two samples, there is evidence that alternative conceptions previously found among A-level students are also commonly held by preservice teachers. A high proportion of preservice chemistry teachers, similar to the A-level students, consider the imperative to obtain a full shell (or other configurations judged stable) and the sharing-out of nuclear attraction as perfectly viable explanatory principles that they include among their “tool-box” of chemical concepts (33) and from which they are quite prepared to select when they seem to be the most salient choice in some chemical context to be explained. The results are broadly consistent with that of previous research that teachers have a somewhat better understanding of chemistry concepts than students but some teachers may still have inadequate understanding of the concepts that they teach (20) or are going to teach, in the case of the preservice teachers. Consistency of Responses The response patterns of individuals are complex, so that a preservice teacher basing a response to one question on a particular alternative conception does not necessarily select
the response based on the same rationale for other questions. So although a response based on the imperative to obtain full shells or the sharing-out of nuclear force may seem the best explanation in one particular question context, the parallel response may not be chosen if on another question some other option offers more salience. This lack of consistency in students’ responses deserves some further comment. In an earlier study, when U.K. secondary and college students completed the Truth about Ionic Bonding diagnostic instrument it was found that some questions based on a “molecular” framework for understanding ionic bonding were commonly considered true. Most respondents agreed that sodium and chlorine could only form one bond; that a bond was the transfer of electrons; that a diagram of a cross-section through an ionic NaCl lattice showed molecules; and that each molecule comprised a single sodium ion and a single chloride ion. Despite this, contradictory statements supporting the conventional electrostatic understanding of ionic bonding were also selected by a majority of respondents (34). Some students agreed with premises based on two competing ways of understanding ionic bonding: the common alternative conceptual framework and the electrostatic model set out in the curriculum. They had acquired both ways of thinking and tended to agree with statements that made sense in terms of one of the available conceptual frameworks. A similar effect seems to be in operation in our present study. A rationale that seems to a preservice teacher to be the most relevant or convincing for one question, may not be the favored candidate for responding to another question. So while many of the preservice teachers (44%) demonstrated the full-shells explanatory principle in responding to question 1 and most (56%) used this rationale in question 3, many fewer, just over a quarter (27%), used the same rationale in question 4 and only about an eighth (12%) selected the related response option in question 5. Similarly, the proportion of preservice teachers selecting responses based on the conservation of force conception was very different in questions 2 (54%) and 4 (19%). While the vast majority of those using this rationale in question 4 had used it in question 2, clearly most of those selecting this rationale on the earlier question found another response option more convincing for question 4. Indeed, cross-tabulation of related response combinations showed that if there was no other compelling distractor in the questions, the preservice teachers were more likely to chose response combinations indicating the same alternative conceptions in different questions: 76% of the preservice teachers who chose the stable octet or noble gas configuration response combination in question 1 (A2) chose a similar combination in question 3 (B4), and 74% of the preservice teachers who chose the stable half-filled subshells response combination in question 8 (B2) chose a similar combination in question 9 (A3). It is tempting to interpret such inconsistency in responses as indicating a lack of commitment to the ideas being used, perhaps implying that the alternative conceptions demonstrated are rather labile and could be readily displaced. Yet these conceptions seem to be applied by preservice teachers in Singapore to a similar extent to that found in A-level stu-
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 5 May 2009 • Journal of Chemical Education
627
Research: Science and Education
dents (10), despite the years of degree-level study. Rather the structure of a multiple-choice instrument constrains students to select the most appealing response option and that may mean choosing between several apparently valid rationales. So in question 4, for example, selecting a response based on the full-shell explanatory principle excludes the response based on conservation of force, and vice versa. Indeed, this type of selection among viable alternatives is hardly to be criticized. Questions 5–10 are all based on comparisons where a range of potentially relevant factors have to be considered and the most pertinent selected for a particular case. To a respondent holding alternative conceptions completing the IEDI, deciding whether disrupting a full shell or the effect of sharing-out nuclear force among fewer electrons is the more significant factor in question 4 may not seem so different from deciding whether increasing electronic repulsion or increasing nuclear charge is more significant in question 5. Recommendations for Teacher Education The present study found that among preservice science teachers preparing to specialize in high school chemistry teaching in Singapore, understanding of the topic of ionization energy was one area where subject-matter knowledge was commonly inadequate. In this study, the preservice teachers in Singapore demonstrated alternative conceptions very similar to those found among Singapore A-level students (10). As the same alternative conceptions have also been found to be prevalent among students in United Kingdom, New Zealand, China, Spain, and the United States (28), it seems highly likely that candidates preparing for chemistry teaching in these and other countries may well have inadequate understanding of this topic, in common with the Singapore preservice teachers. We would suggest that preservice programs worldwide should audit this aspect of preservice teachers’ subject matter knowledge. The IEDI is a published tool that could be used in such subject matter knowledge auditing. Two-tier diagnostic instruments play a useful role in auditing preservice teachers’ subject-matter knowledge and incorporating curriculum content knowledge in a teacher preparation program. Diagnostic instruments such as the IEDI, the Qualitative Analysis Diagnostic Instrument (32), and the Chemical Bonding Diagnostic Instrument (35) have been administered, since 2001, to preservice chemistry teachers in the first author’s institution. After taking the tests, the preservice teachers would discuss their answers in small groups, present them to the rest of the class, and resolve any differences with their classmates. The feedback received has been that these sessions were valuable to the preservice teachers as the tests and the follow-up discussions clarified many things that they took for granted, or were not aware of, in the various topics. For ionization energy, the discussion focused on the “stability” of an octet, full subshell and half-filled subshells of electrons, basic electrostatic (Coulombic) principles, and the interactions of the range of relevant factors in determining the trend of ionization energies. The preservice teachers were challenged to explain why octets, full subshells or half-filled subshells of electrons conferred “stability” to ions and many of them would reply that they had learned this in school. They did not realize
628
that these electronic configurations had no intrinsic stability (36). These were merely heuristics to help students draw the electronic configurations of ionic or covalent compounds or to remember the anomalies in the trends of ionization energies across periods 2 and 3. Discussions then proceeded to why the common ions encountered in secondary chemistry have only one specific charge, for example, why the sodium ion is singlycharged and not doubly-charged or triply-charged; the energy considerations involved in losing inner-shell electrons or adding electrons to an outer subshell are seldom discussed in school. To question the conservation-of-force thinking, basic electrostatic principles were introduced. (There were a number of preservice teachers who had not studied physics at the A-level and had not encountered them previously; others had forgotten them or did not relate these principles to ionization energy.) The importance of considering all relevant factors and how these factors may work in opposing directions were highlighted in the deliberations of the trends of ionization energies. It has to be noted that studies have shown that alternative conceptions can be very resistant to change, especially where these conceptions are intelligible, plausible, and fruitful (37) for their owners. It seems that the conceptions identified in the study have become familiar (“comfortable”) and “meaningful” ways of explaining chemical phenomena; they may even be taught by teachers, found in textbooks (10), and accepted in examinations. Thus, it may not be easy to create dissatisfaction with the alternative conceptions and motivate the preservice teachers to address them simply by confronting these conceptions (37, 38). Further research is needed to explore the best approaches to responding to these conceptions, and to guiding students (including preservice teachers) toward more scientifically acceptable models for understanding ionization energy. Conclusions This study showed that, in general, a significant number of preservice chemistry teachers did not adequately understand the factors influencing ionization energy and the trend of ionization energy across period 3. The prevalence of alternative conceptions among preservice teachers was similar to that previously found among high school students, despite additional years of undergraduate education (23). This reiterates the need to audit subject matter knowledge and not assume that a university degree assures adequate understanding of teaching topics (20). Diagnostic instruments, such as the IEDI, are useful tools for such auditing purposes. Teachers need to be aware of their own alternative conceptions and difficulties in the various topics in the curriculum, and these alternative conceptions and difficulties have to be addressed in teacher education programs (18, 39). Experiencing cognitive conflicts will also give teachers experience in working through “the process of conceptual change” so that they are better equipped to “be able to support their own students in doing so” (39). Hopefully, with this awareness, the transmission of alternative conceptions to future generations of students by teachers will be minimized; the number of students affected by teaching based upon poor subject-matter knowledge can be quite significant given the numbers taught over a teaching career (40).
Journal of Chemical Education • Vol. 86 No. 5 May 2009 • www.JCE.DivCHED.org • © Division of Chemical Education
Research: Science and Education
Literature Cited 1. Taber, K. S. Chem. Educ. Res. Pract. 2003, 4, 149–169. http:// www.uoi.gr/cerp/2003_May/pdf/05Taber.pdf (accessed Jan 2009). 2. Carr, M. Res. Sci. Educ. 1984, 14, 97–103. 3. Jensen, W. B. J. Chem. Educ. 1998, 75, 679–687. 4. Taber, K. S.; Tan, K. C. D. Int. J. Sci. Math. Educ. 2007, 5, 375–392. 5. Ausubel, D. P. The Acquisition and Retention of Knowledge: A Cognitive View; Kluwer Academic Publishers: Dordrecht, 2000. 6. Johnstone, A. H. Chem. Educ. Res. Pract. 2000, 1, 9–15. http:// www.uoi.gr/cerp/2000_January/pdf/056johnstonef.pdf (accessed Jan 2009). 7. Taber, K. S. Int. J. Sci. Educ. 1998, 20, 597–608. 8. Taber, K. S. Int. J. Sci. Educ. 1998, 20, 1001–1014. 9. Taber, K. S. Sch. Sci. Rev. 1999, 81 (295), 97–104. 10. Tan, K. C. D.; Taber, K. S.; Goh, N. K.; Chia, L. S. Chem. Educ. Res. Pract. 2005, 6, 180–197. http://www.rsc.org/images/Tanpaper_tcm18-41069.pdf (accessed Jan 2009). 11. Driver, R.; Leach, J.; Millar, R.; Scott, P. Young People’s Images of Science; Open University Press: Buckingham, 1996. 12. Talanquer, V. J. Chem. Educ. 2006, 83, 811–816. 13. Solomon, J. Getting to Know about Energy – in School and Society; Falmer Press: London, 1992. 14. Gilbert, J. K.; Osborne, R. J.; Fensham, P. J. Sci. Educ. 1982, 66, 623–633. 15. Taber, K. S. Int. J. Sci. Educ. 2008, 30, 1027–1053. 16. Taber, K . S. Int. J. Sci. Educ. 2008, DOI :10.1080/ 09500690701589404. 17. Taber, K. S. Sci. Educ. 2005, 89, 94–116. 18. Lenton, G.; Turner, L. Sch. Sci. Rev. 1999, 81 (295), 67–72. 19. Wandersee, J. H.; Mintzes, J. J.; Novak, J. D. Research on Alternative Conceptions in Science. In Handbook of Research on Science Teaching and Learning; Gabel, D. L., Ed.; Macmillan: New York, 1994; pp 177–210. 20. Abell, S. K. Research on Science Teacher Knowledge. In Handbook of Research on Science Education; Abell, S. K., Lederman, N. G., Eds.; Lawrence Erlbaum Associates: Mahwah, NJ, 2007; pp 1105–1149. 21. Quilez-Pardo, J.; Solaz-Portoles, J. J. J. Res. Sci. Teaching. 1995, 32, 939–957. 22. De Jong, O.; Acampo, J.; Verdonk, A. J. Res. Sci. Teaching. 1995, 32, 1097–1110. 23. Tan, K. C. D. Can. J. Sci. Math. Tech. Educ. 2005, 5, 7–20. 24. De Jong, O.; Veal, W. R.; Van Driel, J. H. Exploring Chemistry Teachers’ Knowledge Base. In Chemistry Education: Towards
25. 26.
27.
28. 29. 30. 31. 32. 33. 34. 35. 36. 37. 38. 39.
40.
Research-Based Practice; Gilbert, J. K., De Jong, O., Justi, R., Treagust, D. F., Van Driel, J. H., Eds.; Kluwer Academic Publishers: Dordrecht, 2002; pp 369–390. Treagust, D. F. Int. J. Sci. Educ. 1988, 10, 159–169. Treagust, D. F. Diagnostic Assessment of Students’ Science Knowledge. In Learning Science in the Schools: Research Reforming Practice; Glynn, S. M., Duit, R., Eds.; Lawrence Erlbaum Associates: Mahwah, NJ, 1995; pp 327–346. Tan, K. C. D.; Goh, N. K.; Chia, L. S.; Taber, K. S. Development of a Two-Tier Multiple Choice Diagnostic Instrument To Determine A-Level Students’ Understanding of Ionization Energy; National Institute of Education: Singapore, 2005. Tan, K. C. D.; Taber, K. S; Liu, X.; Coll, R. K.; Lorenzo, M.; Li, J.; Goh, N. K.; Chia, L. S. Int. J. Sci. Educ. 2008, 30, 265–285. SPSS for Windows, Release 14.0.0; SPSS Inc.: Chicago, Il, 2005 Peterson, R. F.; Treagust, D. F. J. Chem. Educ. 1989, 66, 459– 460. Peterson, R. F.; Treagust, D. F.; Garnett, P. J. Res. Sci. Teaching 1989, 26, 301–314. Tan, K. C. D.; Goh, N. K.; Chia, L. S.; Treagust, D. F. J. Res. Sci. Teaching 2002, 39, 283–301. Taber, K. S. Sch. Sci. Rev. 1995, 76 (276), 91–95. Taber, K. S. Sch. Sci. Rev. 1997, 78 (285), 85–95. Tan, K. C. D.; Treagust, D. F. Sch. Sci. Rev. 1999, 81 (294), 75–83. Cann, P. J. Chem. Educ. 2000, 77, 1056–1061. Posner, G. J.; Strike, K. A.; Hewson, P. W.; Gertzog, W. A. Sci. Educ. 1982, 66, 211–227. Pintrich, P. J.; Marx, R. W.; Boyle, R. A. Rev. Educ. Res. 1993, 63, 167–200. Russell, T.; Martin, A. K. Learning To Teach Science. In Handbook of Research on Science Education; Abell, S. K., Lederman, N. G., Eds.; Lawrence Erlbaum Associates: Mahwah, NJ, 2007; pp 1151–1178. Valanides, N. Chem. Educ. Res. Pract. 2000, 1, 249–262. http:// www.uoi.gr/cerp/2000_May/pdf/33-06valanides.pdf (accessed Jan 2009).
Supporting JCE Online Material http://www.jce.divched.org/Journal/Issues/2009/May/abs623.html Abstract and keywords Full text (PDF) Links to cited URLs and JCE articles Supplement Complete IEDI and learning outcomes
© Division of Chemical Education • www.JCE.DivCHED.org • Vol. 86 No. 5 May 2009 • Journal of Chemical Education
629
