• Bulletin of the Korean Chemical Society
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• v.33 no.7
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• pp.2341-2344
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• 2012

A molecular orbital study is presented of the magnetic coupling in the one-dimensional vanadium oxide $Ba_2V_3O_9$ with a bridge formed by two different types of $VO_4$ tetrahedra. The concept of complementary versus counter-complementary effect has been used to explain the structural origin of the magnetic behavior of the compound. Namely, the observed antiferromagnetic coupling is dominated by the orbital complementarity of the V(1) tetrahedra sharing only one oxygen corner with two adjacent $VO_6$ octahedra. The second type of V(2) tetrahedra does not provide a noticeable contribution to the magnetic coupling due to the orbital counter-complementarity of the bridging ligand.

• Journal of the Korean Chemical Society
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• v.51 no.5
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• pp.447-458
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• 2007

The purpose of this study was to explore high school teacher's and students' perceptions of learning difficulties of the ‘chemical bond' unit of the Chemistry II in the 7th national curriculum. The participants in this study were consisted of a teacher and his students(85) from the Chemistry II classrooms: they all answered to the questionnaire, and then some students and the teacher were interviewed individually. The results showed that there were big differences between the teacher's and his students' perceptions of 1) the most difficult unit for understanding; 2) concepts they learned; and 3) the most difficult concept for understanding in the classroom. Students thought that electro-negativity unit was the most difficult to understand while teacher thought molecular structure unit was the hardest unit to teach. And teacher taught all 32 subjects of chemical bond unit to students, but some students could not remember they learned all of them. Most difficult parts for students to understand were ‘Coulomb force' and ‘dipole moment', while the most difficult part for the teacher to teach was ‘the conceptual difference between atomic bond and intermolecular force'. The reasons caused the students' learning difficulties were analyzed and discussed based on the interview data, and then further study was presented.

• 한국정보디스플레이학회:학술대회논문집
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• 2003.07a
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• pp.1164-1167
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• 2003

Recently CRT is getting flatted, As change of CRT trend from normal type to Flat type, the material of Shadow Mask was also changed from AK(Aluminum Killed) to Invar(Fe-Ni alloy) materials Until now we have used just AK(Aluminum Killed) for normal type TV(not flat type), but main raw material of shadow mask component was changed. . However recently Invar(Fe-Ni alloy) materials, which has advantage of Low Thermal Expansion and High Strength, has been developed as well as applying in mass production as CRT's trend has become more flat and fine pitch. As main raw material of shadow mask component was changed, conditions of process were changed. One of them, the importance of pre-etching process (assistant process for developing & etching) is improved because there are so many particles in the pre-etching bath because of Ni compounds. Since the solubility of Ni in pre-etching solvent is very low related to Fe's, so the compounds of Ni happen to make particles.(the solubility of Fe is twenty times Ni's) that particles happen to make process troubles and NG productions so to clear the particles we had to established high cost filtering system, but it is useless. As time goes by the quantity of particles (Ni compounds) was increased because of the capability of filtering system was not enough, the particles was produced continuous in bath, and it make quality problems. Hence we tried to develop the new pre-etching solution to remove the particles (Ni compounds) and to cost down the filtering system's running cost. But in improving the solution we discovered the new pre-etching solution made the PR developing better. In former solution there were three kinds of chemistry (COOH)2 , H2O2 , H2S04 .first the function of (COOH)2 is drilling the surface of Invar, during this mechanism Ni compounds occurred. Second the function of H202 is removing the PR fringe (half UV exposure zone on PR(PVA)), Third the function of H2S04 is the catalysis of (COOH)2 In those, (COOH)2 was the main reason to make the Ni compounds. So to improve the solutions we had to change (COOH)2 to the other material. the chemistry we improved was a complex chemistry based on H2S04 . after using this chemistry the particles problem was disappeared and there was another advantage cut down the PR fringe. The New solution made the function of H202 better so the PR developing improved. To be direct the catalyst of the new solution helped the H202. anyway First thing after change the solution the quality of shadow Mask for flat color TV was improved & the yield also improved. But the more important thing is how to control the new solution. So we accepted the new concept which was the degree of freshness. The degree of freshness is based on non-reacted solution which was 100% ( the degree of freshness) and calculated the melted Ni quantity as time goes by. So we made the gauging liner plot. In conclusion, many companies tried to make fine pitched Shadow Mask ,generally to make quality jump up it needed a lot of cost & persons .in this case the shift of core material made it possible.

• Journal of the Korean Chemical Society
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• v.33 no.6
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• pp.588-595
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• 1989

Log K, ${\Delta}$H and ${\Delta}$S for the complexation of $La^{3+},\;Ce^{3+}$ and $Eu^{3+}$with various multidentate ligand containing crown ether, diaza crown ether and diamine ether have been determined in methanol and acetonitril solutions at $25^{\circ}C$ by solution calorimetric titration method. The greater stability constant of $La^{3+}$-15C5 than those of 18C6 diaza [2.2] in methanol are discussed in terms of the size of metal ion and the ligand cavity and of metal ion solvation. The stabilities of $Ce^{3+}$ and $La^{3+}$ ion complexes with a various multidentate ligand in acetonitril are in the order of (diamine ether)<18C6<15C5$Ce^{3+}$, $La^{3+}$ and $Eu^{3+}$-diaza [2.2] complexes in acetonitril are increased with the following order: $Eu^{3+}$ < $La^{3+}$ < $Ce^{3+}$, that is increasing order of the optimum size and of the charge density of metal ion.

• Journal of the Korean Chemical Society
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• v.43 no.5
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• pp.578-588
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• 1999

The purpose of this study is to develope the more effective chemistry teaching strategy through analyzing the demanded cognitive levels of contents in high school chemistry I textbooks and the cognitive levels of students who learn these textbooks. For this purpose, the levets of cognitive development stages of 821 second grade students of high schools in Seoul City were anaIyzed using the GALT short version test. The demanded cognitive levels of understanding the contents of chemistry I textbooks in high school were analyzed using the curriculum analysis taxonomy developed by CSMS (Concept in Secondaly Mathematics and Science) program of the Great Britain. The resuIts showed that the proportion of students in the concrete operational stage, the transition stage, and the formal operational stage was l0.7%, 43.0% and 46.3%, respectively. The demanded levels of textbook contents were mostly the early formal operational stages. The concepts demanded the level of the late formal operational stage were 'atomic and molecular weight', 'stoichiometry of chemical reaction', and 'periodic properties of elements'. The results will be helpful for teachers in knowing what concepts are difficult for students to understand and in planning strategies for teaching those concepts. To demonstrate the application of the results obtained in this study, an example of developing teaching strategy which includes the adjustment of cognitive level of contents was shown.

• Journal of the Korean Chemical Society
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• v.33 no.3
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• pp.287-294
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• 1989

The optimum condition for the separation of priority pollutant phenols using isocratic elution has been determined. The elution behavior of eleven phenols has been also studied to interpret the retention. The reversed phase liquid chromatographic methods were performed on a ${\mu}$-Bondapak $C_{18}$ column with methanol-water, acetonitrile-water, and THF water mixtures as mobile phases. The COF method, where Snyder's solvent triangle concept was combined with a mixture-design statistical technique, was used to optimize the strength and selectivity of solvents for the separation of phenols. The optimum solvent composition, which gives a complete separation of eleven phenols, was found to be $MeOH:ACN:H_2O$ = 7:40:53. The plots of ln k' vs. -${\Delta}H^{\circ}$ and ${\Sigma}{\pi}$ of phenols showed relatively good linearities. Effect of van der Waals volume, pi-energy and hydrogen bonding on the retention of phenols were investigated. The following equation with the correlation coefficient of 0.9927 for ACN-water solvent system was obtained; $log^{k'}=2.515{\times}10^{-2}VWV-1.301{\times}10^{-1}E-3.674{\times}10^{-1}$

• Journal of Science Education
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• v.45 no.1
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• pp.1-10
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• 2021

In this study, we analyzed the relationship between the physical science domain of TIMSS 2019 and the Korean science curriculum. Twelve subjects are presented in the physical science domain of the TIMSS 2019 4th grade evaluation framework. Research group consisting of elementary and middle school teachers and science education experts, a total of 12, participated to analyze in which grade these subjects were included in the Korea 2009 revised and 2015 revised science curriculum. As a results of analyzing whether the achievement standards of the TIMSS 2019 evaluation framework and Korean science curriculum are consistent, the subjects pertinent to chemistry like 'chemical changes in everyday life,' 'heat transfer,' and 'electricity and simple electrical circuits' appeared not covered at all until the 4th grade curriculum in Korea. Given that the TIMSS 2019 evaluation framework is an international achievement standard, we are proposing to improve the Korean curriculum as follows: first, for the development of the next science curriculum, there is a need for science curriculum organized from the 1st grade of elementary school to connect the content and scope of chemistry in elementary, middle, and high schools as a whole including the Nuri curriculum. Second, as an alternative to the problem of suitability of learning volume and level of learning, it is possible to think of a method to readjust the grade of dealing with related concepts by lowering the difficulty or simplifying the concept. Third, it is necessary to discuss about introducing essential concepts and standard terms into Korea science curriculum according to international trends.

• Journal of the Korean Chemical Society
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• v.66 no.3
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• pp.228-242
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• 2022

In this study, the educational effect was investigated by providing a teaching program so that pre-service chemistry teachers could apply model ignorance education to teacher training practice. The teaching program was constructed in consideration of the sensemaking concept proposed in the study of Odden & Russ and the process of teacher sensemaking proposed by Asli et al. The subjects of this study were 23 pre-service teachers in the 4th year of chemistry education department at a teacher training university in the central region of Korea. In order to form a sensemaking for the model's ignorance education, the teaching program consisted of four stages; the initial idea generation stage, cognition of model's ignorance stage in a inconsistent situation, the lesson strategy construction stage for model ignorance education, and lesson plan & practice stage during teacher training practice. In the first stage of this program, pre-service teachers' initial ideas about the Arrhenius model and Bronsted-Lowry model of acid-base reaction, and the electron transfer model of the oxidation-reduction reaction were investigated. In the second stage, inconsistant situation that cannot be explained by the knowledge of model was presented to recognize the ignorance of the model. The third stage was to develop the teaching ability of model's ignorance through textbook analysis and lesson strategy composition activities. As a final stage, during the teacher training practice, the pre-service teachers were asked to plan and practice the implementation of the model's ignorance education. Through the teaching program to form a sensemaking for ignorance education of the models, pre-service teachers had come to recognize the ignorance of the model, acquired ability to organize and execute lesson strategies reflecting model ignorance, and acquired recognition of the educational value and necessity of teaching the ignorance of models.

• Journal of The Korean Association For Science Education
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• v.26 no.2
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• pp.246-257
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• 2006

TIMSS (Trends in International Mathematics and Science Study) aims to produce reliable and internationally comparable indicators of student achievement. The TIMSS science achievement scale summarizes student performance on test items designed to measure a wide range of student knowledge and proficiency. This study analyzed Korean middle school students' science achievement at the advanced and high international benchmarks of the four benchmark levels of the benchmarks classified in TIMSS 2003 in light of science content areas (physics, chemistry, biology, earth science, and environmental science) and item characteristics. The average percent correct on items at the advanced benchmark by Korean students was highest in physics followed by earth science, biology, chemistry, and environmental science, whereas internationally the order was earth science, chemistry, biology, physics and lastly environmental science. Korean students performed relatively better in physics yet somewhat worse in chemistry than other top-performing countries. According to item analysis, Korean students reaching the advanced international benchmark understood some fundamentals of scientific investigation, but demonstrated weakness in written explanations of scientific principles, abstract science concept comprehension, and application of scientific concepts to solve quantitative problems. In addition, Korean students reaching the high international benchmark demonstrated relative weak conceptual understanding of ecology compared with other countries.

• Journal of the Korean Chemical Society
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• v.60 no.5
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• pp.362-373
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• 2016

In this study, ionic compound in the science textbooks developed under the 2009 revised national curriculum were analyzed in terms of the scientific concept and model description and the student understanding through the questionnaires. Analysis of textbooks was performed for science2 of middle school and chemistry I & II of high school. Questionnaire was carried out with 194 students including middle school 2nd grade and high school 1st-3rd grade. The results are as follows: First, as a result of analysis of textbooks, scientific concepts and models used to explain the ionic compound showed differences depending on the types of textbooks. In addition, scientific models were provided with or without explanation for the scientific concepts. Second, analysis of the questionnaire showed that students didn’t properly understood scientific concepts and models in the ion formation, stoichiometric ratio between ions.