In the Classroom edited by
View from My Classroom
David L. Byrum Flowing Wells High School Tuscon, AZ 85705-3099
Nomenclature Made Practical: Student Discovery of the Nomenclature Rules
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Michael C. Wirtz,* Joan Kaufmann, and Gary Hawley Science Department, Concord Academy, Concord, MA 01742; *
[email protected] The chemical nomenclature of inorganic compounds is typically introduced early in many introductory chemistry courses at both the university and secondary school levels. A brief survey of several popular general chemistry textbooks reveals that this subject is often covered in the first few chapters (1–10).1 From the perspective of the student chemical nomenclature is a series of complex rules and situations involving unfamiliar concepts, such as transition-metal oxidation states and polyatomic ions. When the focus of our general chemistry curriculum shifted to emphasize studentled discovery experiences over pure content (i.e., sacrificing content for more laboratory work and student-led group work), nomenclature became an unwieldy beast with no logical home, frequently derailing student interest in chemistry right from the beginning of the course. This problem led us to create the following series of nomenclature activities that better suited the demands of our curriculum and the needs and interests of our students. Many articles in this Journal have been devoted to the topic of nomenclature. These articles present notable ideas on using computers to reinforce nomenclature rules (11, 12), games and activities designed to make learning nomenclature fun for students (13, 14), and systems to guide students through nomenclature (15). One extensive series of articles was devoted exclusively to nomenclature and its development (16–32). Herein we present a creative and practical method to teach chemical nomenclature to students in an introductory chemistry course utilizing the discovery-learning model. Inorganic compounds are grouped into four categories: binary ionic compounds of the main-group elements, binary ionic compounds containing variably charged cations, ionic compounds containing polyatomic ions, and binary compounds of the nonmetals. The formal introduction of each category of compounds is handled as a separate activity and is interspersed throughout the first semester to provide context and to avoid confronting the student with all of the nomenclature rules at once. Through these discrete and manageable units, the student discovers the patterns of the nomenclature rules by examining a series of named inorganic compounds and the corresponding chemical formulas. It should be noted that this method is not the only experience students have with the naming of compounds; these activities are used to introduce the rules to students. Their understanding and proficiency with the rules is then emphasized through discussions of their findings as well as a series of traditional practice problems.
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The Activities
Activity One: Binary Ionic Compounds Composed of Main-Group Elements The first activity pertains to the nomenclature rules for binary ionic compounds containing only main-group elements. Before activity one is used, students must be familiar with several basic concepts beginning with the differences between metals, metalloids, and nonmetals. The characteristics of these classes of elements are discussed and their locations on the periodic table of elements are noted. Terms such as atoms, protons, neutrons, electrons, nucleus, and compounds are a part of the working vocabulary of the course prior to this activity, with many students having some sense of these concepts in previous science experiences. After formally introducing these concepts, it is then possible to introduce ions as charged chemical species. Monatomic cations and anions are discussed and then related to the previously established classes of elements, the metals and the nonmetals. A discussion of polyatomic ions is delayed until later in the course. The students are then introduced to ionic compounds as a class of compounds composed of metallic cations and nonmetallic anions. The periodic table is referenced again while examining the trends in the charges of ions of the main-group elements.2 It is imperative that students understand that compounds do not carry any charge and that the ratio of cations to anions must provide a neutral chemical species. Once the student is comfortable with the previous ideas, the stage is set to use activity one. In activity one, the student is provided the following series of binary ionic compounds as both a formula unit and in written form using the Stock nomenclature system: sodium bromide, aluminum phosphide, calcium fluoride, potassium oxide, and magnesium nitride. With only the correct name and formula unit at their disposal, as well as the explicit instruction not to use outside resources (the Internet or the textbook), students are asked to record their observations about the written form and chemical formula. These observations are then converted in to a working set of rules by which this type of compound can be named or converted into formula units. Included in activity one is the opportunity to practice naming compounds and to write chemical formulas once the rules have been determined. Because activity one limits itself to binary compounds of the main-group elements, students need only to recognize the following patterns: the cation precedes the anion, the
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name of the metal remains unchanged while the name of the nonmetal has assumed an -ide ending, and the chemical formula is charge neutral. Some students may be savvy enough to recognize what rules were not used based on previous experiences, specifically the exclusion of prefixes such as those used in the naming of molecules. The observations and rules that the students create are shared aloud and the problems are reviewed before the activity is complete. Activity one, as with all the activities, works well as an in-class exercise completed in pairs or small groups and is easily completed in less than forty minutes. Once students are familiar with the expectations of the nomenclature activities, subsequent activities can be used as an out-of-class assignment.
Activity Two: Binary Ionic Compounds Containing Variably Charged Cations Activity two teaches students the Stock nomenclature system for binary ionic compounds where the metal cation has more than a single possible charge. The concept of variability in the charge of cations is introduced after using the periodic table of elements as a guide to writing the electron configurations of various elements and ions. By delaying the discussion of multiple oxidation states until the introduction of electron configurations, students more easily understand why these oxidation states arise and how they are represented in the names of ionic compounds. Students are told that most of the metals that are not in group I or group II will likely have more than one possible charge when found as a cation. The use of silver and zinc cations are avoided in this activity to help the students understand the general patterns, though they later learn that silver is always a +1 cation and zinc is always a +2 cation. In this activity a second set of compounds containing both binary ionic compounds with variably charged cations and binary ionic compounds of main-group elements is presented to the students. Both types of compounds are included to reinforce the concepts from activity one and to guide the student in discovering a new set of rules. This set includes iron(III) oxide, iron(II) chloride, lead(II) sulfide, aluminum phosphide, copper(II) fluoride, tin(IV) iodide, and potassium bromide. As with activity one, students again are instructed not to use any outside sources in completing the activity. The goal is for the student to recognize that Stock nomenclature rules for binary ionic compounds containing variably charged cations are similar to the rules for binary ionic compounds containing main-group elements. At the completion of activity two, students come to realize that both groups of compounds utilize the same basic nomenclature rules, with the exception that a Roman numeral must follow a cation that can possibly have more than one charge. It is helpful to discuss why the main-group elements do not require the Roman numeral while the transition metals do. Additional practice problems are provided at the end of the activity to allow students to practice using the nomenclature rules. As in activity one, the observations and rules are shared aloud and the solutions to the naming exercises are reviewed.
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Activity Three: Ionic Compounds Containing Polyatomic Ions All the material in our curriculum prior to the use of activity three is easily accessible without the concept of polyatomic ions; therefore, polyatomic ions enter the student vernacular during a unit on reaction types.3 By this time, students are quite familiar with binary ionic compounds and the expectations of the nomenclature activities. A brief discussion of polyatomic ions and a list of common polyatomic ions precede this activity. The activity, itself, has the same structure as the previous two activities (i.e., determination of the rules and practice exercises). The list of compounds for this activity includes ammonium sulfide, cobalt(II) sulfate, iron(III) hydroxide, calcium phosphate, and ammonium nitrate. In activity three, the previous discovery that the cation precedes the anion is emphasized, demonstrating that not all cations are metals such as in the case of the ammonium salts. Once again concepts from previous activities are reinforced as new concepts are introduced; the usage of Roman numerals as introduced in activity two is again seen in the cobalt(II) sulfate example. The ammonium nitrate example leads students to discover that common elements are not “grouped up” in ionic compounds unless they are in a polyatomic ion. For example, students often ask why ammonium nitrate is written as NH4NO3 and not N2H4O3. This presents an opportunity to teach students that polyatomic ions are chemical species that remain together as a unit regardless of the respective partner cation or anion. This is a characteristic of compounds containing polyatomic ions that proves to be especially important in the context of writing and balancing double replacement reactions with compounds. As with previous activities, additional practice problems are provided, the observations and rules are shared aloud, and the solutions to the naming exercises are reviewed.
Activity Four: Nomenclature of Binary Compounds of the Nonmetals Binary compounds of the nonmetals are the final group of compounds covered and are introduced in activity four. As such, the nomenclature rules of this class are woven in to a unit that includes the covalent bond, Lewis structures, and model building. Activity four is appropriate at this point in the curriculum because students are working with many of these compounds in a different context. Students are familiar with the concept of a molecular compound as a chemical combination of two nonmetals owing to encounters in other units; however this is the first formal presentation of the nomenclature rules for molecular compounds.4 A series of nitrogencontaining compounds consisting of nitrogen trifluoride, nitrogen monoxide, nitrogen dioxide, dinitrogen monoxide, and dinitrogen tetroxide comprise the group of compounds used to discover the nomenclature rules of molecular compounds. Already familiar with the -ide ending of binary ionic compounds, the student should observe its continued usage in molecular compounds. The use of prefixes is readily apparent to most students, though many fail to recognize the absence of the mono- prefix from the first element in a
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molecular compound. As with previous activities, additional practice problems are provided, the observations and rules are shared aloud, and the solutions to the naming exercises are reviewed.
Board of Trustees, Jake Dresden, Sandy Stott, Patty Hager, and Brian Giannino-Racine for their support of our summer work from which much of these activities originated. Jotham W. Coe and Max Hall are thanked for their helpful editing, comments, and encouragement.
Conclusion W
The approach outlined in this article towards the introduction and teaching of chemical nomenclature and the Stock nomenclature system has worked well in our curriculum. This method allows the presentation of chemical nomenclature to fit our departmental philosophy of supporting student discovery in the classroom and laboratory. Students are not relegated to memorizing a series of rules, but rather are engaged as learners in deducing these rules for themselves. These activities can be easily adapted to the curriculum at other institutions as well. By segmenting the compound types, the activities can be appropriately placed at any point within a curriculum. An instructor has the flexibility to use the activities in an order that suits his or her course, provided the students understand the specific pieces of background information outlined previously. Once the expectations surrounding these activities are understood by the student, these activities work well as assignments to be completed outside of class time or as exercises for pairs of students to complete during class time. The latter approach allows the instructor to circulate through the classroom and provide feedback to students on their efforts. In either setting, the activities promote student independence and deductive reasoning as a problem-solving skill. At this point, we have chosen not to expand this approach to the nomenclature of acids owing to the needs of our curriculum.5 However, this could be easily accomplished by using the series of acids containing chlorine: hydrochloric acid, hypochlorous acid, chlorous acid, chloric acid, and perchloric acid. Student reaction to this method has generally been positive. Prior to the introduction of this method, nomenclature was frequently listed on course evaluations as the least interesting topic of the year. Since its introduction a few years ago, chemical nomenclature appears less frequently as the least interesting topic on evaluations, though students who view nomenclature as an exercise in memorization still balk at it in any form. More importantly, students seem to take hold of the concepts faster and retain the ideas longer. Nomenclature taught using this method does not require more teaching time and can even save time if the latter activities are used as out-of-class assignments. It is estimated that when nomenclature was taught as a series of rules early in the course and without significant context, students did not understand the material as well nor retain it as long. Anecdotal evidence to support this statement is provided by the noticeable ease with which students internalize a new set of nomenclature rules and improved nomenclature quiz averages. Acknowledgments The authors wish to thank our students for their willingness to try these activities and the Concord Academy
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Supplemental Material
Instructions for the students for the four activities are available in this issue of JCE Online. Notes 1. The textbook that we use to support our general chemistry curriculum, Malone’s Basic Concepts of Chemistry, 7th ed., does not introduce nomenclature until chapter four. Two of the textbooks surveyed seemingly recognize the difficulty students have in learning nomenclature and offer solutions. Burns delays the nomenclature discussion completely until chapter six of his book, while Whitten et al. introduce a few compounds in the second chapter but delay a full discussion of nomenclature until the fourth chapter. 2. At this point in the course, no formal explanation is provided as to why these ions have a particular charge. That discussion is reserved for later in the course after a study of periodic trends, valence electrons, and electron configurations. 3. Prior to the introduction of polyatomic ions, units on measurement, classification of matter, atomic structure, and energy have been covered. The material in these units works well without the need for polyatomic ions. Students are aware that such species exist; however no time has been devoted to covering the material in any meaningful way. 4. Molecular compounds are formally introduced as chemical species during the unit on reaction types, mostly in conjunction with combination reactions. Students learn to balance equations earlier in the year. However, many of the examples used to balance equations involve binary ionic compounds, which by that point, students are able to name. 5. Prioritizing student experience and discovery over pure content in our curriculum means that certain topics, such as the nomenclature of acids, are not covered as extensively as in previous years. Because we limit the examples of acids used in the course, students become familiar with the nomenclature of particular acids but do not spend time learning these rules, instead devoting time and energy to other discovery experiences.
Literature Cited 1. Brady, J. E.; Russell, J. W.; Holum, J. R. Chemistry: Matter and Its Changes, 3rd ed.; Wiley: New York, 2000; pp 81–87. 2. Brown, T. L.; Lemay, E. H.; Bursten, B. E.; Burdge, J. R. Chemistry: The Central Science, 9th ed.; Prentice Hall: Upper Saddle River, NJ, 2003; pp 56–62. 3. Burns, R. A. Fundamentals of Chemistry, 4th ed.; Prentice Hall: Upper Saddle River, NJ, 2003; pp 159–165. 4. Chang, R. Chemistry, 7th ed.; McGraw–Hill: New York, 2002; pp 53–61. 5. Hill, J. W.; Petrucci, R. H. General Chemistry: An Integrated Approach, 3rd ed.; Prentice Hall: Upper Saddle River, NJ, 2002; pp 51–60.
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In the Classroom 6. Kotz, J. C.; Treichel, P. M.; Weaver, G. C. Chemistry and Chemical Reactivity, 6th ed.; Brooks/Cole: Toronto, 2006; pp 103–115. 7. Malone, L. J. Basic Concepts of Chemistry, 7th ed.; Wiley: New York, 2004; pp 100–111. 8. Silberburg, M. S. Chemistry: The Molecular Nature of Matter and Change, 3rd ed.; McGraw–Hill: New York, 2003; pp 63–70. 9. Whitten, K. W.; Davis, R. E.; Peck, M. L. General Chemistry, 6th ed.; Harcourt: Orlando, FL, 2000; pp 162–164. 10. Zumdahl, S. S; Zumdahl, S. A. Chemistry, 5th ed.; Houghton Mifflin: Boston, 2000; pp 60–71. 11. Shaw, D. J. Chem. Educ. 2003, 80, 711. 12. Cassen, T. J. Chem. Educ. 1981, 58, 49. 13. Chimeno, J. J. Chem. Educ. 2000, 77, 144. 14. Crute, T. D. J. Chem. Educ. 2000, 77, 481. 15. Lind, G. J. Chem. Educ. 1992, 69, 613. 16. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1978, 55, 30–31. 17. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1977, 54, 610–611. 18. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1977, 54, 509–510. 19. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1977, 54, 299–300. 20. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ.
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1977, 54, 30. 21. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1976, 53, 773–774. 22. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1976, 53, 495. 23. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1976, 53, 495. 24. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1976, 53, 355. 25. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1976, 53, 354. 26. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1975, 52, 793–795. 27. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1974, 51, 468–469. 28. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1973, 50, 123–124. 29. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1972, 49, 49–51. 30. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1971, 48, 433–434. 31. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1971, 48, 594–596. 32. Fernelius, W. C.; Loening, K.; Adams, R. M. J. Chem. Educ. 1971, 48, 730–731.
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