Design and Evaluation of a One-Semester General Chemistry Course

Article pubs.acs.org/jchemeduc

Cite This: J. Chem. Educ. XXXX, XXX, XXX−XXX

Design and Evaluation of a One-Semester General Chemistry Course for Undergraduate Life Science Majors Carly Schnoebelen, Marcy H. Towns, Jean Chmielewski,* and Christine A. Hrycyna* Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States S Supporting Information *

ABSTRACT: The chemistry curriculum for undergraduate life science majors at Purdue University has been transformed to better meet the needs of this student population and prepare them for future success. The curriculum, called the 1-2-1 curriculum, includes four consecutive and integrated semesters of instruction in general chemistry, organic chemistry, and biochemistry, taken by students in their first two years. As part of this curriculum, a one-semester general chemistry course, General Chemistry with a Biological Focus (GCBF), was created and evaluated. The course covers all topics typically taught in general chemistry, but with a shift in emphasis toward topics relevant to chemistry in biological systems. Students who took this new course performed better in subsequent organic chemistry courses compared with their peers who took a traditional two-semester general chemistry course. KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Curriculum, Testing/Assessment, Bioorganic Chemistry, Nonmajor Courses

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INTRODUCTION How do we better meet the diverse needs of the students in our classes to prepare them for their futures? Particularly for large introductory classes that serve students with varying educational and career goals, this can be a difficult question to answer. In general chemistry, where the vast majority of students will not go on to become chemists, chemistry education researchers and practitioners have advocated for and enacted a variety of changes in curricula.1−7 One population that has received considerable attention is students in the biological and life sciences, including premedical students.8,9 These students require fundamental coursework in chemistry, typically encompassing general chemistry, organic chemistry, and, increasingly, biochemistry. Recent changes to the Medical College Admissions Test (MCAT) reflect an increased emphasis on the chemistry underlying biological systems.10 While national documents emphasize the need for curriculum reform to meet these changing goals, they do not specify how this is to be accomplished or prescribe any particular curricular approach, leaving these decisions to departments and individual faculty members.11,12 An analysis of exams created and distributed by the American Chemical Society (ACS) over the past 20 years found that many topics relevant to chemistry in biological systems are not often assessed or taught in general chemistry, which suggests a missed opportunity to help students build connections between chemistry and biology.13 Initially at Purdue University and then in partnership with the National Experiment in Undergraduate Science Education (NEXUS) Project sponsored by the Howard Hughes Medical Institute (HHMI), we have transformed the chemistry curriculum for undergraduate life science majors.14 In the new curriculum, students enroll in an integrated sequential © XXXX American Chemical Society and Division of Chemical Education, Inc.

four-semester biologically relevant course series composed of one semester of general chemistry, two semesters of organic chemistry, and one semester of biochemistry in their first two years of study. This curriculum, called the 1-2-1 curriculum, is shown in Table 1. As the first part of this transformation, a rigorous one-semester general chemistry course, titled General Chemistry with a Biological Focus (GCBF), was created and evaluated.

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CURRICULUM CHANGE AND MOTIVATION Prior to creation of the 1-2-1 curriculum, students majoring in biology and other life sciences, along with a variety of other science and engineering majors, enrolled in a two-semester general chemistry sequence that covered traditional topics. These courses were followed by two semesters of organic chemistry that were usually not aligned nor informed by the content in the general chemistry courses. In this endeavor, we collaborated to create the 1-2-1 sequence to better meet the specific needs of life science students. Guided by Scientific Foundations for Future Physicians,9 MR5,10 and Vision and Change,8 we developed learning goals to prepare students for upper-level coursework in biology and biochemistry, undergraduate research, and professional school entrance exams such as the MCAT. In order to achieve the desired course integration, improved content alignment among general chemistry, organic chemistry, and biochemistry was sought. The learning objectives for biochemistry and organic chemistry were threaded through and connected to the learning objectives in general chemistry, which resulted in a lens through which the Received: November 13, 2017 Revised: March 9, 2018

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DOI: 10.1021/acs.jchemed.7b00869 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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Table 1. Comparison of Previous and Revised 1-2-1 Curriculum by Semester and Year Previous Curriculum

Revised Curriculum (1-2-1)

Year

Fall

Spring

Fall

Spring

Freshman Sophomore Junior (or later)

General Chemistry I Organic Chemistry I Biochemistry

General Chemistry II Organic Chemistry II

General Chemistry with a Biological Focus Organic Chemistry II with a Biological Focus

Organic Chemistry I with a Biological Focus Biochemistry: A Molecular Approach

include electromagnetic radiation, quantum theory, ionic solids (crystal structures), nuclear chemistry, calorimetry, nomenclature, electrolytic cells, and quantitative treatment of colligative properties. Overall the focus of GCBF is shifted more toward the second half of a traditional two-semester general chemistry sequence, with most topics typically taught in the first semester being covered in the first third of the class. The focus is also more on building a qualitative understanding, supported by quantitative problem solving, in contrast to traditional general chemistry’s heavy emphasis on quantitative problem solving.17,18 In general chemistry, the goal is for students to build foundational knowledge of the chemistry in biological contexts and to begin making connections between biology and chemistry content. To accomplish this goal, students are introduced to chemistry concepts, which are then contextualized using a variety of biological examples. In a more traditional approach, students initially learn chemistry fundamentals and then wait until a later biochemistry course to apply concepts to biological systems. The general pattern followed in instruction is to present a chemistry topic and then show how it can be applied to a biological context to illustrate how the underlying principles are the same. The beginning of the course introduces students to chemistry fundamentals from an atoms-first perspective, including atomic structure, periodic trends, and bonding. This format lays the foundation for discussing molecular structure and how Lewis structures can be used to predict physical and chemical properties of substances on the basis of an understanding of molecular geometry, hybridization, and intermolecular forces.19 The focus is on carbon-based molecules that students will see the following semester in organic chemistry as well as compounds containing phosphorus and sulfur that play important roles in biochemistry, such as ATP. To illustrate how the structure−property relationships apply to biological systems, students are shown the structures and interactions of large biological molecules such as DNA and proteins. In particular, the peptide bond is presented as an example of how electron delocalization impacts molecular geometry that gives rise to higher-order protein structure. The next section of the course is devoted to the study of chemical reactions and kinetics. Students are introduced to collision theory and mathematical models for the kinetics of gas-phase reactions and reactions in solution. Immediately following, enzyme kinetics is discussed, including the Michaelis−Menten model and the effects of different types of inhibitors on kinetic parameters. Enzyme kinetics is not typically part of a traditional general chemistry course, but it represents an important application to biological systems. We want students to appreciate how enzymes work as catalysts to speed up and control reactions in biological systems on the basis of the same underlying principles that govern the kinetics of all chemical reactions. The discussion of chemical kinetics also includes a brief introduction to nuclear reactions, with a

content of general chemistry was structured and presented to students. This curricular transformation involved the creation of a one-semester general chemistry course emphasizing topics relevant to the chemistry education of life science students, the details of which will be described later. In addition, the entire curriculum was infused with relevant biological examples to tie the chemistry content to the contexts in which students are likely to apply their knowledge. The overarching goal of the 12-1 curriculum is for students to apply their knowledge of chemistry to understanding biological systems at the molecular level, a focus that begins in general chemistry and is carried through organic chemistry and biochemistry. Practical considerations also served as an impetus for the design of the new curriculum. Approximately 60−70% of the students who complete the 1-2-1 curriculum indicate that they are pursuing a preprofessional track, including medical school, dental school, and veterinary school. Since most premedical students take the MCAT in their junior year, there was motivation for students to complete their chemistry coursework, including biochemistry, in their sophomore year. Previously, life science students took a biochemistry course later in their junior or senior year, if at all. This curricular transformation also creates more opportunities for students to take advanced courses for which biochemistry is a prerequisite and engage in undergraduate research earlier in their college careers.

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GENERAL CHEMISTRY WITH A BIOLOGICAL FOCUS (GCBF) The overarching goal of the curriculum is for students to apply their chemistry knowledge to understand biological systems at the molecular level. The new one-semester general chemistry course, GCBF, was designed specifically for life science majors and emphasizes fundamental principles of chemistry relevant to organic chemistry and biochemistry. The course focuses on building deep understanding of core concepts while still covering all of the topics that are traditionally part of general chemistry.15,16 GCBF is a five-credit course, while each semester of the two-semester sequence is four credits, in order to provide sufficient class time to cover all of the topics. An overview of the topics covered in the course can be found in the Supporting Information. Although all of the topics traditionally covered in general chemistry are included in GCBF, certain topics are emphasized while others are de-emphasized depending on their relevance to chemistry in biological systems. Topics that receive increased attention in GCBF relative to the traditional general chemistry curriculum are resonance structures, intermolecular forces with emphasis on hydrogen-bonding interactions, organic functional groups, acid−base equilibrium, buffers, thermodynamics of living systems, and electrochemistry in the context of catabolic reactions and the electron transport chain. These topics are emphasized because of their importance to organic chemistry and biochemistry.9,17 Topics that receive less attention compared with a traditional general chemistry curriculum B

DOI: 10.1021/acs.jchemed.7b00869 J. Chem. Educ. XXXX, XXX, XXX−XXX

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edge.23,24 At present, the evaluation of the curriculum focuses primarily on the lecture portion of the course.

focus on applications to nuclear medicine, such as positron emission tomography (PET) imaging. The last part of the course is devoted to thermodynamics and equilibrium in the context of acid−base and oxidation− reduction reactions. Equilibrium is studied first from both a qualitative and quantitative perspective. Concepts of equilibrium are then applied to acid−base reactions. There is a particular emphasis on understanding and using Ka and pKa values to predict and rationalize relative acid strength, as is commonly done in organic chemistry and biochemistry. Students are also introduced to the arrow-pushing formalism used by organic chemists to represent electron flow in the context of Lewis acid−base theory, which is typically not included in general chemistry, as evidenced by the anchoring concepts content map (ACCM) for general chemistry.20,21 Buffers are also discussed extensively as an application of acid− base equilibrium that is especially important to biological systems. Phosphate and carbonic acid buffer systems are presented as examples of physiological buffers that control the body’s environment on the basis of the same principles underlying chemical equilibrium in all systems. Thermodynamics begins with a brief introduction to enthalpy and entropy, which builds to a discussion of Gibbs free energy, the driver of reactions in biological systems. Examples such as ATP coupling illustrate strategies used by cells to make nonspontaneous reactions occur. Thermodynamics is then applied to oxidation−reduction reactions, which are an important part of cellular metabolism. Students are introduced to redox chemistry and determination of oxidation numbers as a tool to track the flow of electrons in a system. The focus is on organic compounds rather than metals and metabolic reactions rather than batteries and electrolytic cells. As a final application of chemistry in a biological context, the electron transport chain and membrane potentials are discussed to illustrate principles of thermodynamics in redox reactions. In this one-semester general chemistry course, students attend three one-hour lectures per week, in contrast to two one-hour lectures per week in the two-semester course. Students also attend a required one-hour recitation section and three-hour laboratory section each week, which are also part of the traditional course. The course is offered every fall semester and was taught by the same professor (one of us, C.A.H.) from 2010 to 2016 during the initial development and refinement of the course. It is now taught by a variety of professors in the biochemistry division of the Chemistry Department. The textbook Chemistry: Atoms First22 is used along with the accompanying online homework system. The integrated laboratory portion of the course involves several contextualized experiments with biological applications. For example, one of the laboratories has students prepare a buffer to simulate buffer systems found in the human body and determine how to restore the buffer to physiological pH after it has been perturbed. Students also do an enzyme kinetics experiment, which is a unique feature of the curriculum since students typically do not encounter this until a later biochemistry course. A schedule of laboratory experiments can be found in the Supporting Information. In addition to introducing students to laboratory techniques in chemistry, the intention of the laboratories is to reinforce and further illustrate applications of chemistry concepts to biological systems. We realize, however, that current evidence from the literature suggests that traditionally structured laboratory experiences may be ineffective at promoting chemistry content knowl-

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STUDENT POPULATION The majority of students who enroll in GCBF are freshmen in their first semester of undergraduate study. Students are required to have taken at least one year of high school chemistry and math up through precalculus (or SAT Math 650 or ACT Math 29) to enroll in the course. Enrollment has increased each year since the course was first offered in Fall 2010, and in Fall 2013 biology majors began taking the course, as shown in Table 2. It should be noted that the numbers in Table 2. Enrollment in GCBF by Major, Fall 2013−Fall 2016 Semester Fall Fall Fall Fall

2013 2014 2015 2016

Total Enrollment, N 323 320 463 519

Biology Majors, N (%) 35 61 171 229

(11) (19) (37) (44)

Prepharmacy Majors, N (%) 269 247 292 273

(83) (77) (63) (53)

Other Majors, N (%) 19 19 5 17

(6) (6) (1) (3)

Table 2 represent students who completed the course and do not include students who dropped before the end of the semester. The number of biology majors increased dramatically from 2014 to 2015, when GCBF officially became the required general chemistry course for students in the biology majors. In the evaluation, data are presented from the Fall 2015 cohort of biology majors. GCBF also enrolls a large number of prepharmacy majors, who then complete the remainder of their chemistry coursework separately in the College of Pharmacy.

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EVALUATION OF THE CURRICULUM To evaluate the impact of the new general chemistry curriculum, we tracked the performance of students in the Fall 2015 cohort. This cohort was followed because it was the first year in which a substantial number of biology majors took GCBF and progressed through the entire 1-2-1 curriculum. Of the biology majors who completed GCBF in Fall 2015, 92% earned an A, B, or C in the course, and the majority of these students enrolled in Organic Chemistry I, the next course in the 1-2-1 sequence, in the subsequent semester, Spring 2016. Student performance data, including course grades and exam scores, were collected from Organic Chemistry I and II in Spring 2016 and Fall 2016, respectively, for students who took the one-semester GCBF course in Fall 2015 as well as students who took the traditional two-semester general chemistry course in either Fall 2014 and Spring 2015 or Spring 2015 and Fall 2015. One of the goals of the new curriculum is to better prepare students for learning organic chemistry, and these measures should reflect achievement of that goal. From a constructivist perspective, learning is influenced strongly by a student’s prior knowledge, so it follows that student learning in organic chemistry would be influenced by previous learning in general chemistry.25 This view of teaching as “preparation for future learning” has been advocated by scholars in education.26 The assumption that underlies this curriculum redesign, and its evaluation, is that students who are better prepared by learning relevant prior knowledge in general chemistry will display increased learning, as reflected by better performance on exams, in organic chemistry. Improved student performance in organic C

DOI: 10.1021/acs.jchemed.7b00869 J. Chem. Educ. XXXX, XXX, XXX−XXX

Journal of Chemical Education

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midterm exams and a final exam accounted for 80% of students’ grades, with an additional 20% from homework assignments. Each student’s lowest exam grade was dropped from the overall grade. Extra credit was given at the instructor’s discretion; grades in the course were not curved. Letter grades were assigned according to a standard grading scale based on the total number of points the student earned in the course, as shown in Table 4.

chemistry has been demonstrated as evidence for the success of other reforms targeting general chemistry.27,28 The same professor (one of us, J.C.) teaches both Organic Chemistry I and II. Both semesters also include a recommended one-hour recitation section taught by graduate teaching assistants and undergraduate teaching interns. Organic chemistry laboratory is a separate course that may be taken concurrently, depending on the requirements of a student’s major. All midterm exams given in both semesters were written by the instructor and comprised short-answer questions. The final exam was cumulative for the entire semester and included approximately 25% multiple-choice questions while the rest of the questions were short-answer. Exams were graded by graduate teaching assistants according to rubrics created by the instructor. The distributions of class standings and academic majors for the two groups of students in Organic Chemistry I are shown in Table 3. Students in these groups had similar backgrounds; one

Table 4. Letter Grade Assignment in Organic Chemistry I and II

Table 3. Student Class Standing and Major College in Organic Chemistry I, Spring 2016

Class standing

Major college

Freshman Sophomore Junior Senior Science Agriculture Health and Human Sciences Pharmacy Engineering Other

GCBF Students (n = 138)

Traditional GC Students (n = 166)

88 11 1 0 85 7 3

11 71 15 3 34 19 35

3 1 1

1 9 2

Points (Total out of 500)

A B C D F

450+ 400−449 350−399 300−349