VSEPR-Plus: Correct Molecular and Electronic ... - ACS Publications

Article Cite This: J. Chem. Educ. 2019, 96, 75−81

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VSEPR-Plus: Correct Molecular and Electronic Structures Can Lead to Better Student Conceptual Models Brian J. Esselman* and Stephen B. Block Department of Chemistry, University of WisconsinMadison, 1101 University Avenue, Madison, Wisconsin 53706, United States

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S Supporting Information *

ABSTRACT: The VSEPR model has well-established limitations in its ability to represent accurate molecular and electronic geometries of simple molecules, which can create a significant need for students to relearn structure and bonding concepts in organic chemistry. We present an alternate method for describing molecular geometries and electronic structures to students that is far more consistent with experimental observations than VSEPR. Our alternate method of teaching structures extends VSEPR to account for conjugation to adjacent π-systems and the experimentally observed nature of lone pairs, which is supported by computational chemistry via WebMO’s HTML-export feature. If implemented, it allows students to reconcile hybridization, valence bond theory, molecular orbital theory, and resonance structures into a single coherent picture of electronic structure and bonding for organic molecules. KEYWORDS: First-Year Undergraduate/General, Second-Year Undergraduate, Curriculum, Organic Chemistry, Misconceptions/Discrepant Events, Computational Chemistry, Covalent Bonding, Molecular Modeling, VSEPR Theory

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chemistry, and higher-level chemistry curricula, in part due to its attractive simplicity. Unfortunately, despite the apparent simplicity, VSEPR limits students’ ability to easily rationalize the reactivity and structure of simple compounds important to general and organic chemistry without the need to unlearn misconceptions. Even with these previous publications, the educational community has not uniformly moved away from embracing the VSEPR model. Indeed, a quick survey of general chemistry textbooks20−30 and organic chemistry textbooks18,31−37 confirms that most still fully employ the VSEPR model to predict a tetrahedral electron-domain geometry for water without discussing its limitations. At least one general chemistry28 and one organic chemistry textbook35 introduce the incorrect electron-domain geometry in water but then attempt to clarify the nonequivalence of the lone pairs in a later section. Unfortunately, neither textbook’s discussion of the correct electronic structure (experimentally determined and computationally estimated) is connected to a new figure or is treated substantially, so it is unlikely that students will update their knowledge and remove their misconception. Loudon’s Organic

good scientific model, and thus a good model for science students to learn, explains the available scientific data and allows the scientist (or student) to extrapolate to related cases and examine those cases by experimentation and observation. Valence shell electron pair repulsion (VSEPR) has long served as the go-to model for students to understand the molecular and electronic structures of simple molecules.1−3 Well before its adoption into the undergraduate curriculum, the photoelectron measurements of many small molecules provided experimental data that VSEPR was unable to rationalize4−7 and are described in several previous works in the chemical education literature.8−18 Shown in Figure 1 are several known examples (not an all-inclusive list) that highlight the shortcomings of the VSEPR model. VSEPR fails to correctly describe the electron-geometry of water (explored further below);9−13,15,17 the electron and molecular geometry of aldehydes, ketones, and carboxylic acid derivatives;4,9,15,16 the structure of metal complexes;14 the molecular geometry of thiols, disulfides, and peroxides;9,13,18 and the molecular and electron-geometry of organic halides.13,16,19 While VSEPR may often predict the correct molecular geometry, it does not always do so and it predicts the geometry from an overly simplistic basis, focusing solely on steric repulsion and ignoring orbital mixing, π-conjugation, dipole−dipole interactions, and hydrogen-bonding. VSEPR persists in high school, general © 2018 American Chemical Society and Division of Chemical Education, Inc.

Received: May 1, 2018 Revised: October 21, 2018 Published: November 13, 2018 75

DOI: 10.1021/acs.jchemed.8b00316 J. Chem. Educ. 2019, 96, 75−81

Journal of Chemical Education

Article

Figure 1. Several of the known cases where VSEPR predicts the incorrect molecular or electron-domain geometry.

Chemistry avoids the VSEPR treatment of water altogether, though it utilizes the p-orbital lone pairs on divalent O atoms later in the textbook without specifically confronting the misconception. It is clear, however, that student misconceptions are often far too entrenched in students’ minds to correct the issue with a simple passage or avoidance.38,39 In addition to its simplicity, perhaps one of the reasons VSEPR persists in the curriculum is that many educators, aware of its flaws, are biased by their own experiences. The individuals who write the textbooks and teach the college courses are, by and large, far more intellectually flexible than their novice students. Furthermore, college-level instructors had success as students by adeptly correcting misconceptions to be successful in their own academic careers. This makes instructors inherently less acutely aware of the challenge many students experience when grappling with new concepts in conflict with previously held knowledge. The teaching of VSEPR is about to face its toughest pedagogical test yet and its incorporation in the curriculum will need to be modified. The ever-decreasing cost of computational power and the generation of student-friendly, low-cost (or free) computational software40−43 places the chemical education community on a trajectory in which computational chemistry will become commonplace in the inorganic, organic, general, and high school chemistry curricula. The chemical education literature features an increasing number of computational chemistry implementations at these levels.10,12,14,44−46 Given the power of computational chemistry to provide students with an understanding that more accurately depicts the experimentally determined geometry and function of molecules, this trend is unlikely to reverse. One day soon, if it has not happened already, a high school student will view a computationally generated depiction of the lone pairs on the oxygen atom in water (Figure 2), ethanol, or diethyl ether and ask their teacher, “Why are the lone pairs not the same? Why is the computer giving me the wrong answer? Why is the O atom not in a tetrahedral geometry?” The high school teacher will likely respond with, “I don’t know why the calculation is getting the wrong lone pairs. Don’t worry about it.” The chemical education community should see this as problematic

Figure 2. VSEPR-predicted equivalent O atom lone pairs and NBOpredicted (B3LYP/6-31G(d)) O atom lone pairs in water.

from both a pedagogical and a scientific perspective. The student has learned an incorrect model that will have to be altered to be able to explain all of the chemical reactivity that the student will encounter in the journey through the chemistry curriculum. This incorrect picture of the lone pairs will persist and will be very difficult to replace with a correct understanding of electron-domain geometry. Second, from a scientific perspective, the VSEPR model is often introduced in the curriculum as fact, rather than as a limited model that does not account for known experimental outcomes and observations. As scientists, we are bound to continually search for models that explain the available data and reject models that cannot account for the known data. We should not intentionally provide our students with a flawed model presented as incontrovertible fact. The time has arrived to embrace a better way of introducing molecular and electronic structures to students; we need a paradigm shift. Other than institutional memory and inertia, the three driving forces that seem to entrench VSEPR in the curriculum are its perceived accuracy, a lack of a viable 76



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locations and hybridizations of the lone pair orbitals, however, require computational chemistry and a molecular orbital (MO) or a natural bond orbital (NBO) calculation. We use B3LYP calculations with students due to their established use in modern research, their ability to predict the electronic structure of molecules with reasonable accuracy, their computational efficiency, and their easy accessibility for students via WebMO. We have found the use of MO or NBO computational outputs in WebMO to be quite convenient while not requiring a significant amount of prior student knowledge about MO or NBO. The focus on the requirement of a p-orbital (or p-rich orbital) to exist at an atom for π-conjugation requires a change to the VSEPR-predicted lone pair locations for many atoms (e.g., ester O atoms, Figure 1). This increased focus allows the instructor to address a common misconception that hybridization changes from one resonance form to another, a student misconception that often persists into organic chemistry. (In fact, for the past several years, our incoming chemistry graduate students have revealed during a TA training activity that some of them have the misconception that the N atom in formamide changes hybridization from sp3 to sp2 in the various resonance structures. The activity is provided in the Supporting Information). If students know that a p-orbital (or a p-rich orbital) is required for π-conjugation, it naturally discourages this misconception of changing hybridization because the students would be less likely to assign a hybridization of sp3 to the N atom using a singly bonded resonance structure of formamide. After the validity of the computational results is established for students, it is possible to convincingly approach the VSEPR flaw that they often find most surprising: the p-rich nature of at least one lone pair in any heteroatom with two or more lone pairs. While it is challenging for students who first learned VSEPR to incorporate this new understanding of p-orbitals, the ability to correctly rationalize the π-conjugation of heteroatoms depends on the correct hybridization of their lone pairs. To support student acceptance of p-orbital lone pairs on heteroatoms, we provide several examples of WebMO outputs of NBO calculations showing the lone pairs of oxygen, sulfur, bromine, and chlorine. Simply seeing the lone pairs of water (Figure 2) makes it impossible to reconcile the tetrahedral electron geometry predicted by VSEPR. At this point, the support of computational chemistry is critical. Students need evidence to counter their preconception, and the necessary photoelectron spectroscopy is beyond the grasp of students at this level. There are numerous benefits to students and their ability to predict chemical structures and reactivity throughout general and organic chemistry. Replacing a VSEPR-only model with a VSEPR-plus model leads to a more straightforward conceptual approach. Several previously described examples are highlighted here.4−18 In each of these cases, a correct understanding of atom and lone pair hybridizations makes understanding the chemical concept much more straightforward. In each case, the electron-geometry predicted by a VSEPR-only approach makes the chemical concept more intellectually awkward to understand. Figure 3 shows the B3LYP/6-31G(d) optimized geometry of formamide. It provides a simple example of the awkward need to reorganize the electron-domain geometry or rehybridize an N atom to rationalize its ability to conjugate to a π-bond. Many students, and some of our incoming graduate student teaching

alternative curricular approach, and a perceived lack of harm to students. We believe that more accurate alternatives exist that are beneficial to students and are now readily accessible due to advancements in computational chemistry. We present below a curricular approach to structure and bonding that goes beyond VSEPR and allows students to reconcile hybridization, valence bond theory, molecular orbital theory, and resonance structures into a single coherent picture of electronic structure and bonding for chemistry students.

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A VIABLE ALTERNATIVE While alternate approaches to teaching students about structure and bonding may have existed, the ready access to computational chemistry and the ability to provide students with computational outputs (at very low to no cost) that are consistent with experimental observations make an alternate approach much more attractive. VSEPR starts, and stops, the discussion of molecular geometry with electron−electron repulsion. Alternatively, a more accurate picture of bonding would result if the model of molecular structures were not limited to electron−electron repulsion, but if this were part of the discussion that included orbital mixing, π-conjugation, dipole−dipole interactions, and hydrogen-bonding. It is difficult for novice students to balance all of these factors to estimate electronic and molecular structures, hence the attraction of the simple VSEPR model. We have developed an alternate curricular approach for the introductory organic chemistry curriculum that seeks to move beyond the prior incomplete and incorrect knowledge with which students enter the course. We immediately demonstrate how a better understanding of bonding can empower them to understand the structures and reactivity that are important for a sound conceptual understanding of organic chemistry. The shift in instruction is 3-fold. First, students encounter computationally accurate molecular and electronic structures using WebMO43 and its HTML-export feature. Second, students are informed that atoms in π-conjugation must have a p-orbital (or p-rich orbital) aligned with the neighboring πsystem and see the resulting π-symmetry orbitals via WebMO. Third, students are instructed that any atom with two or more lone pairs will have at least one lone pair in a p-orbital, which is supported by computational data. Together, these adaptations build upon the VSEPR-predicted geometries and correct them to provide students with a better working knowledge of molecular geometries and structure. To be clear, this approach is a second-order perturbation of VSEPR thinking (VSEPRplus) and not a wholesale rejection of the entrenched model for a rigorous molecular orbital or valence bond theory approach to structures and bonding. Thus, perhaps this instructional model serves as a small step forward in chemical education that will lead to better student understanding of structures and bonding by the entire community. The availability of computationally accurate structures provides students with more confidence in the accuracy of any two-dimensional representation and in any inferences that they make on the basis of that image related to structure and reactivity. Students are not left to wonder if their drawings on paper or their construction of a physical model represent the molecule effectively; they can confirm or reject their structural prediction using these computational outputs. For those who prefer experimental structures, the molecular geometries of gas-phase structures determined by μ-wave spectroscopy or solid-phase X-ray crystal structures could be used. The 77



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UW-Madison Chemistry teaching assistant (TA) training. VSEPR is firmly entrenched for many new TAs, causing them to struggle to recognize that the hybridization and electrondomain geometry cannot change from one resonance form to another. Only the overapplication of VSEPR caused them to believe that the N atom would be trigonal pyramidal, and thus sp3 hybridized, in the first place. This misconception could be avoided by intentionally adding the consideration of πconjugation as an important factor influencing the electrondomain geometry of an atom. The incorrect assumption that a divalent oxygen atom with two lone pairs has a tetrahedral electron-geometry is one of the more problematic assumptions of VSEPR with respect to its impact on the understanding of organic molecules. While it has already been pointed out that this is incorrect even for nonconjugated O atoms, such as in water, ethanol, and diethyl ether, it is problematic for conjugated systems. Due to the prominence of water in every VSEPR discussion, students have a very difficult time viewing a divalent O atom in any electrongeometry other than tetrahedral. Commonly, students struggle to rationalize the reactivity of carboxylic acid derivatives, the electron-donating effect of alkoxy (−OR) substituents, and the aromaticity of furan in large part because they do not properly consider the nature (orientation, hybridization) of the lone pairs on the O atom (Figure 4). In order to rationalize the electrophilicity of carboxylic acids, esters, and their derivatives or the electron-donation of the −OR group, π-conjugation of the system must be understood. Unlike the electron-domain geometry of an N atom that could be roughly tetrahedral (VSEPR-predicted), trigonal planar (with the ability to πconjugate), or somewhere in between (where sterics and conjugation compete), the electron-domain geometry of an O atom is not so ambiguous. It is made to seem ambiguous only due to an application of VSEPR. With two lone pairs, an O atom will naturally have a p-orbital lone pair (Figure 2). Thus, no change of the O atom is required for it to conjugate with

Figure 3. Important resonance structures of formamide with its NBOpredicted O atom lone pairs, N atom lone pair, and resulting π1 molecular orbital. The N atom does not adopt a trigonal pyramidal geometry as predicted by VSEPR, but instead has a nearly trigonal planar geometry.

assistants, struggle with a misconception of the changing hybridization from sp3 to sp2 for the nitrogen atom in formamide, which could be avoided simply by teaching that the N atom in formamide will adopt a near planar geometry to allow for π-conjugation. The Supporting Information includes an example quiz question addressing this misconception with organic chemistry students and an example exercise used in the

Figure 4. Examples of O atom p-orbital conjugation with the π-systems of formic acid, anisole, and furan. 78



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the adjacent π-bond, and the conjugation is not strange, but an obvious result of the alignment of the p-orbital lone pair. An understanding of the electron-donating ability of the O atom to aromatic systems like anisole and furan is critical for understanding aromaticity, electrophilic aromatic substitutions (EAS), and NMR chemical shifts. The resonance structures, shown in Figure 4 for formic acid, anisole, and furan, are commonly shown in organic textbooks to explain the electrondonating ability of the O atom. The resonance structures of these oxygen-containing compounds require a p-orbital or prich orbital on the O atom to allow it to interact with the adjacent π-systems. Students who have a deeply embedded image of tetrahedral-oriented lone pairs from VSEPR struggle to understand the overlap of the O atom orbital with the πsystem and must rely on a rehybridization of the O atom lone pair. Possibly most powerful in the VSEPR-plus approach is the easier identification of furan as an aromatic molecule. Students often initially struggle to identify the aromaticity of furan using the Hückel 4n + 2 π-electron rule. Entrenched beliefs of VSEPR-style lone pairs make it difficult to determine if the conjugated π-electron count should be four, six, or eight. As stated previously, students can build a work-around in their thought process to rehybridize the O atom and move one of the lone pairs into a p-orbital. But, once again, the analysis is more straightforward if the students begin from the knowledge that the divalent O atom has a p-orbital lone pair. This principle can be quite easily extrapolated to other atoms with two or more lone pairs, and the exact same analysis could be made for the sulfur analogues, thioanisole, or thiophene. For aryl halides, it is a challenge to rationalize the EAS chemistry and the NMR chemical shifts of the 1H atoms attached to an aromatic ring without an understanding of the electron-withdrawing impact of the halogen’s connection to a carbon atom and the electron-donating impact of the halogen p-orbital. Once again, starting from a VSEPR perspective, students are forced to rehybridize their VSEPR-rationalized orbitals on the substituent halogen atoms. Whereas with a correct understanding that the halogen substituent has at least one p-orbital lone pair, the electron-donating impact of the lone pair on the conjugated system is a natural outcome.

empirical observation or computational support to provide evidence for the lone pair hybridizations. This document provides a viable alternative to instructors who wish to teach a more correct model of bonding and structure that will serve students more effectively in organic chemistry. Additionally, a recommended problem set and answer key used in conjunction with this handout are provided in the Supporting Information, along with two example quizzes demonstrating how structure and bonding could be assessed in the introductory organic chemistry course.

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ASSESSMENT OF STUDENT LEARNING To assess the ability of students to correctly predict the electronic structure of small organic molecules, several questions were embedded in a quiz that occurred in the final week of a summer (8-week) course of introductory organic chemistry (85 students). The full quiz and answer key are available in the Supporting Information. Students were asked to identify the hybridization of each lone pair in 4nitropyridine and furan, determine the number of electrons in cyclic π-conjugation, and state whether or not the molecule contains an aromatic ring. This rudimentary assessment (results in Table 1) of the student learning revealed that Table 1. End-of-Semester Ability of Students To Correctly Assign Lone Pair Hybridizations and Analyze π-Systems

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INTRODUCTORY READING AND WEBMO HANDOUT To allow instructors to adopt a VSEPR-plus model of bonding and structure, we provide a supplement to the typical introduction of electronic and molecular structures in Organic Chemistry. This document, entitled “Introductory Organic ChemistryStructure and Bonding Primer”, in the Supporting Information, has been utilized with over 1800 students at the University of WisconsinMadison. While written to be used with Loudon’s Organic Chemistry sixth edition, the supplemental handout can easily be modified for use with any organic textbook. The handout provides a coherent picture of bonding and structure and openly acknowledges the limitations of Lewis Structures and VSEPR. We focus on electron-repulsion, π-conjugation, and orbital hybridization as the most important factors determining molecular shapes. Each of the issues raised within this article with the VSEPR-only approach are addressed. In order to support the statement that atoms with two or more lone pairs have at least one lone pair in a p-orbital, we use embedded MO and NBO computational output files from WebMO. This addition is critical for students at the organic chemistry or general chemistry level; they need some

a

N = 85 students. bOnly electrons within the ring were included in the π-electron count.

most of the students were able to correctly assign the hybridization of all three lone pairs. This assessment occurred well removed from the start of the term when the structure and bonding handout was first implemented. The students, however, received instruction throughout the term that was consistent with that handout. Furthermore, this quiz was taken after instruction on aromaticity in which the correct hybridization of lone pairs is critical and was reinforced for students. Rather than a rigorous exploration of students’ ability to correctly conceptualize lone pair orbitals using bonding concepts that extend beyond VSEPR, we believe it provides a proof-of-concept that students can rationalize lone pairs correctly if given correct instruction. Further educational research on this topic should investigate optimizing the method of introducing correct bonding concepts to students 79



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(4) Keller, P. R.; Taylor, J. W.; Grimm, F. A.; Carlson, T. A. Angleresolved photoelectron spectroscopy of formaldehyde and methanol. Chem. Phys. 1984, 90 (1), 147−153. (5) Hall, M. B. Stereochemical Activity of s Orbitals. Inorg. Chem. 1978, 17 (8), 2261−9. (6) Jorgensen, W. L.; Salem, L. The Organic Chemist’s Book of Orbitals; Academic Press: New York, 1973; p 305. (7) Turner, D. W.; Baker, C.; Baker, A. D.; Brundle, C. R. Molecular Photoelectron Spectroscopy; A Handbook of Helium 584 A Spectra; John Wiley & Sons: New York, 1970; p 386. (8) House, J. E. Orbital Hybridization and Repulsion in Structural Analogies and Fallacies. Chemical Educator 2018, 23, 82−86. (9) Clauss, A. D.; Nelsen, S. F.; Ayoub, M.; Moore, J. W.; Landis, C. R.; Weinhold, F. Rabbit-ears Hybrids, VSEPR Sterics, and Other Orbital Anachronisms. Chem. Educ. Res. Pract. 2014, 15 (4), 417− 434. (10) Esselman, B. J.; Hill, N. J. Integration of Computational Chemistry into the Undergraduate Organic Chemistry Laboratory Curriculum. J. Chem. Educ. 2016, 93 (5), 932−936. (11) Laing, M. No Rabbit Ears on Water. The Structure of the Water Molecule: What Should We Tell the Students? J. Chem. Educ. 1987, 64 (2), 124−128. (12) Clauss, A. D.; Nelsen, S. F. Integrating Computational Molecular Modeling into the Undergraduate Organic Chemistry Curriculum. J. Chem. Educ. 2009, 86 (8), 955−958. (13) Anslyn, E. V.; Dougherty, D. A. Modern Physical Organic Chemistry, 1st ed.; University Science Books: Sausalito, CA, 2004. (14) McNaught, I. J. Testing and Extending VSEPR with WebMO and MOPAC or GAMESS. J. Chem. Educ. 2011, 88 (4), 421−425. (15) Zdanovskaia, M. A.; Schwarz, C. E.; Habib, A. D.; Hill, N. J.; Esselman, B. J. Access to Computational Chemistry for Community Colleges via WebMO. J. Chem. Educ. 2018, DOI: 10.1021/ acs.jchemed.8b00310. (16) Esselman, B. J.; Hill, N. J. Integrating Computational Chemistry into an Organic Chemistry Laboratory Curriculum using WebMO. ACS Symp. Ser. 2018, manuscript in revision. (17) Donnelly, J.; Hernández, F. E. Trends in Bond Dissociation Energies for the Homolytic Cleavage of Successive Molecular Bonds. J. Chem. Educ. 2018, 95 (9), 1672−1678. (18) Loudon, M. G.; Parise, J. A. Organic Chemistry, 6th ed.; Roberts and Company Publishers: Greenwood Village, CO, 2016. (19) Demaison, J.; Breidung, J.; Thiel, W.; Papousek, D. The Equilibrium Structure of Methyl Fluoride. Struct. Chem. 1999, 10 (2), 129−133. (20) Brown, T. E.; LeMay, H. E.; Bursten, B. E.; Murphy, C.; Woodward, P.; Stoltzfus, M. E. Chemistry: The Central Science, 14th ed.; Pearson Education Limited: Harlow, United Kingdom, 2017. (21) Burdge, J.; Driessen, M. Introductory Chemistry: An Atoms First Approach, 1st ed.; McGraw-Hill: New York, NY, 2015. (22) Chang, R. Chemistry, 8th ed.; McGraw-Hill: New York, NY, 2005. (23) Ebbing, D. D.; Gammon, S. D. General Chemistry, 8th ed.; Houghton Mifflin Company: Boston, MA, 2008; pp 374−400. (24) Gilbert, T. R.; Kirss, R. V.; Foster, N.; Bretz, S. L.; Davies, G. Chemistry: The Science in Context, 5th ed.; W. W. Norton & Company: New York, NY, 2018. (25) Kotz, J. C.; Treichel, P. M.; Townsend, J. Chemistry and Chemical Reactivity, 7th ed.; Cengage, Inc.: Stamford, CT, 2008. (26) Moore, J. W.; Stanitski, C. L. Chemistry: The Molecular Science, 5th ed.; Cengage Learning: Stamford, CT, 2015. (27) Oxtoby, D. W.; Gillis, H. P.; Campion, A. Principles of Modern Chemistry, 7th ed.; Brooks/Cole: Belmont, CA, 2012. (28) Petrucci, R. H.; Herring, F. G.; Madura, J. D.; Bissonnette, C. General Chemistry: Principles and Modern Applications, 10th ed.; Pearson Canada: Toronto, Canada, 2011. (29) Silberberg, M. S. Chemistry: The Molecular Nature of Matter and Change; McGraw-Hill: New York, NY, 2009. (30) Zumdahl, S. S.; Zumdahl, S. A. Chemistry, 9th ed.; Brooks/ Cole: Belmont, CA, 2018.

that are consistent with known experimental and computational results.

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SUMMARY AND CONCLUSION While the initial adoption of VSEPR seemed reasonable, as it provided instructors with a simple way to have students predict and rationalize molecular shapes, it was well-known at the time that VSEPR’s accuracy was limited even with simple molecules and functional groups. Its incorporation into the curriculum was based upon its simplicity, but without a full appreciation for how it would limit the understanding and rationalization of chemical reactivity. As scientists and scientific educators, we must be willing to discard old models based upon misconceptions and misunderstandings when a new, more accurate model becomes available and accessible to students. With the rise of computational chemistry in the undergraduate curriculum, the time has come for us to teach a better model of structure and bonding that will allow students to better rationalize chemical phenomena.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available on the ACS Publications website at DOI: 10.1021/acs.jchemed.8b00316. Structure and bonding handout (PDF) Sample quizzes and answer keys (PDF) Sample structure and bonding problem set with answer key (PDF) TA training resonance structure activity (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Brian J. Esselman: 0000-0002-9385-8078 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge the National Science Foundation for support of shared departmental computing resources (NSF-CHE-0840494). All jobs were run on the Sunbird computer cluster at UW-Madison. We thank Allen Clauss, Steve Nelsen, Mohamed Ayoub, John Moore, Clark Landis, and Frank Weinhold for their previous work and guidance. We thank Alan Silver for his technical assistance posting WebMOexported files to a website and Jim Maynard’s photographical assistance. B.J.E. thanks Robert McMahon for teaching him the correct hybridization of the O-atoms in water and formaldehyde. We thank the other instructors, particularly Jia Zhou and Aubrey Ellison, and students at the University of Wisconsin who have assisted and supported in this endeavor.

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REFERENCES

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