We investigated students' knowledge constructions of basic quantum chemistry concepts, namely atomic orbitals, the Schrödinger equation, molecular orbitals, hybridization, and chemical bonding. Ausubel's theory of meaningful learning provided the theoretical framework and phenomenography the method of analysis. The semistructured interview with 19 second-year chemistry students supplied the data. We identified four levels of explanations in the students' answers. In addition, the scientific knowledge claims reflected three main levels of models. By combining levels of explanations with levels of models, we derived four categories. Two of the categories are shades of variation in the rote-learning part of a continuum, while the other two categories are in the meaningful-learning part. All students possessed alternative conceptions some of which occurred within certain categories, while others spanned more categories. The insistence on the deterministic models of the atom, the misinterpretation of models, and the poor understanding of the current quantum concepts are main problems in the learning of the basic quantum chemistry concepts. ß

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A major driving force in the current effort to reform science education is the conviction that it is vital for our students to develop their higher-order cognitive skills capacity in order to function effectively in our modem, complex science and technology-based society. In line with this rationale, this study focuses on the use of examinations for studying student performance in chemistry examination on items that require higher-order cognitive skills (HOCS) or lower-order cognitive skills (LOCS). This usage of examinations is explored and demonstrated via "post-factum" data analysis of two case studies: the General Examination (in chemistry) and the Panhellenic Chemistry Competition administered nationally in Greece for secondary-school graduates in 1991. The main findings were: (a) students performed considerably lower on questions requiring HOCS than on those requiring LOCS; (b) performance on questions requiring HOCS may not correlate with that on questions requiring LOCS for which affective factors, LOt:S-orientation in teaching and the extent of prior examination preparation may be responsible; and (c) examinations that contain items of both types can be effectively used to identify HOCS-and LOCS-students within various contexts of chemistry teaching. Based on the above and previous related studies, the fostering of students' HOCS by appropriate teaching and assessment strategies is advocated.The acquisition of higher-order cognitive skills (HOCS) by our students, beyond the so far dominating lower-order cognitive skills (LOCS), is a major instructional goal in contemporary science teaching. The HOCS capabilities such as question asking (ZoUer, 1987), problem solving, decision making, and critical thinking-all of which require evaluative thinking (ZoUer, 1993)-are considered by many to be the most important learning outcomes to which good teaching should aim (Lehman,

Students start the undergraduate quantum chemistry course with incomplete knowledge and many conceptual difficulties about quantum-chemical concepts. This work investigated the impact an undergraduate quantum chemistry course has on students' knowledge and understanding of atomic orbitals, molecular orbitals and related concepts. A "post-factum" analysis of examination data from this course reveals that students: do not have a clear understanding of the concepts of atomic and molecular orbitals as well as of Slater determinants; have difficulty in understanding the conceptual similarity between real and complex mathematical forms of atomic orbitals; confuse the various atomic orbital representations; and, do not realise the approximate nature of atomic orbitals for many-electron atoms. Difficulties with other related concepts are revealed also. Some promising strategies for instruction and suggestions for secondary and general chemistry curricula are discussed.Teaching quantum-chemical theories of atomic and molecular structure in general chemistry or introductory inorganic chemistry courses is now a well established tradition in first-year chemistry and other science departments. Besides, atomic and molecular orbitals are part of the upper secondary curriculum in many countries. There is, however, an increasing number of educators who are against the use of the orbital and related quantum chemical concepts in basic chemistry courses

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