Ionic bonding is a fundamental topic in high. Ionic bonding games actively engage students in processing key concepts

Transcription

1 Ionic bonding games actively engage students in processing key concepts Mollianne G. Logerwell and Donna R. Sterling Ionic bonding is a fundamental topic in high school chemistry, yet it continues to be a concept that students struggle to understand. Even if they understand atomic structure and ion formation, it can be difficult for students to visualize how ions fit together to form compounds. This article describes several engaging activities that help students gain a better understanding of ionic compound formation and how to write ionic formulas. December p27-33logerwell.indd 27 11/7/2007 3:52:30 PM

2 Introductory activity Before using these activities, the teacher should review ion formation with the class. Specifically, students need to remember that ions are formed when atoms either gain or lose electrons; losing electrons results in an ion with a positive charge, while gaining electrons results in an ion with a negative charge; the number of electrons gained or lost indicates the magnitude of the ion s charge; and the periodic table helps to predict what ions an element will make. One quick and easy way to reinforce these concepts is with a review sheet. Such a worksheet allows students to step through the process from electron configuration to ion formation for a variety of elements (Figures 1 and 2). The teacher can use such a review sheet as a diagnostic assessment, either in class or as homework, to determine if students are ready for the next step. Once students are comfortable predicting what ion will be formed for a particular element, they are ready to be introduced to the wonderful world of ionic compounds! Ionic bonding cards The Ionic Card activity is a great way to introduce how ions combine. By physically manipulating ions to make compounds, students are able to build visual models of how ions join in whole number ratios to form neutral compounds. To begin the activity, students cut out cards that symbolize positive and negative ions of various charges (Figure 3). Cards that have missing pieces represent cations (atoms that have lost electrons), while those that have extra pieces represent anions (atoms that have gained electrons). The number of removed segments equals the number of electrons removed, and the number of added segments equals the number of electrons added. From this information, students can determine the charge of the ion. For example, a card with two segments removed would represent an ion with a 2+ charge because it is missing two electrons, while a card with three segments added would represent an ion with a 3- charge because it has three added electrons. Students then label the cards with an appropriate element or polyatomic ion. Based on the information learned in a previous unit on the periodic table, students FIGURE 1 Review sheet for ion formation. Element Al O Na Cl Mg Electron configuration Number of valence electrons Commonly gain or lose electrons? How many? Ion formed Column on the periodic table FIGURE 2 Sample of a partially completed review sheet for ion formation. Element Al O Na Cl Mg Electron configuration Number of valence electrons Commonly gain or lose electrons? How many? Ion formed Column on the periodic table 28 The Science Teacher p27-33logerwell.indd 28 11/7/2007 3:52:31 PM

3 Fun with Ionic Compounds FIGURE 3 Cards for Ionic Card activity. Blank cards: Sample compound: Sample compound: Sample compound: determine which element or polyatomic ion corresponds to the charge indicated by the card. If a card represents an ion with a 1- charge, for example, it could be labeled with any halogen (e.g., chlorine) or suitable polyatomic ion (e.g., nitrate). Students can be given a list of specific elements to use or allowed to choose their own. Next, the teacher explains that the ions positive and negative charges must neutralize each other in order to make a compound. For example, a magnesium ion (which has a 2+ charge) could be balanced with one oxide ion (which has a 2- charge) or two chloride ions (each of which have a 1- charge). When writing the compound s formula, students are reminded that the symbol for the cation is written first followed by the symbol for the anion. Subscripts after each symbol indicate the number of each ion present (e.g., MgO and MgCl 2 ). The formula for aluminum oxide, Al 2 O 3, therefore, means that there are two aluminum ions and three oxide ions present in the compound. Additionally, if polyatomic ions are used, students should be instructed to use parentheses when more than one of a polyatomic ion is needed in the compound (e.g., Ca(NO 3 ) 2 ). Students can now physically combine the cards to make various compounds. Again, the teacher can give students a list of compounds to make or allow students to create their own. How the teacher wishes to assess the activity will dictate how students proceed with their work. If this activity is being used as an infor- December p27-33logerwell.indd 29 11/7/2007 3:52:31 PM

4 mal assignment, the teacher can circulate around the room and give individual feedback to students as they make each compound. Alternatively, students can glue or tape the ions together on a sheet of paper, write the compounds formulas, and turn in their work for either diagnostic assessment or for a formal grade. The activity can also be expanded by having students name the compounds. Ionic bonding games Once students have a basic understanding of ionic compound formation, games are a fun alternative to worksheets as a method of reinforcing the concepts of formula writing and naming. These activities can be assessed informally by having students check each other s work as the game progresses or by the teacher circulating and giving feedback. If the teacher desires, students could also list the formulas and/or names of the compounds formed and submit them for a grade. It is recommended that all playing pieces (e.g., wheels, cards, game boards) be laminated in order to increase their longevity. Wheel of Formulas For the Wheel of Formulas game, the teacher creates a wheel of anions (Figure 4) and attaches an arrow through the center with a brass fastener to form a spinner. To play, students spin the arrow to determine the compound s anion. For the cation, students can either pick from a teacher-generated list or choose their own. Once both ions have been established, students write the formula and name for the compound formed. This game can be played individually or in groups of three to four students. Depending on the complexity desired, the anions charges can be left off or names, instead of symbols, can be used on the wheel. Additionally, another wheel can be made with cations so that students have to spin both to determine what combination of ions to use. FIGURE 4 Example of a wheel of anions for Wheel of Formulas. 30 The Science Teacher p27-33logerwell.indd 30 11/7/2007 3:52:31 PM

5 Fun with Ionic Compounds FIGURE 5 Examples of cards for Formula Rummy and Fishing for Formulas (with symbols and with names). December p27-33logerwell.indd 31 11/16/ :54:33 AM

6 Formula Rummy For Formula Rummy, the teacher creates a set of approximately 50 cards for each group that contains symbols for various elements and polyatomic ions (Figure 5, p. 31). Each card does not have to be unique; duplicates work well. The object of the game is to combine element cards and/or polyatomic ion cards to form appropriate compounds. In groups of three to four students, players are dealt seven cards. The remainder of the cards in the set are placed face down in the center to form the stockpile. The top card of the stockpile is turned face-up to form the discard pile. To play the game, the first student picks the top card from either the stockpile or the discard pile. After drawing a card, any combination of cards now in the student s hand that make a valid ionic compound can be played. For example, if a student has two sodium cards and a sulfate card, the student would lay them down to form sodium sulfate. When finished, the student places one card face up on the discard pile. Play continues in a clockwise rotation until all of one student s cards have been played. Depending on the amount of time available, the teacher may allow students to play more than one compound per turn. The more plays per turn, the faster the game. Additionally, to increase the difficulty of the game, the cards can be made without charges or with names instead of symbols. Fishing for Formulas Fishing for Formulas uses the same card set developed for Formula Rummy. Instead of playing rummy, however, students follow the rules for Go Fish. Again, the object of the game is to collect cards that form valid ionic compounds. As before, the teacher must decide if students can play more than one compound per turn, and if cards are made without charges or with names instead of symbols. Each of these variations can be used at different times, depending on the time available and the difficulty level desired. Chemistry: The Board Game For Chemistry: The Board Game, the teacher makes a game board composed of squares that contain element symbols and a starting point (Figure 6). A set of cation cards and a set of anion cards are also needed (the rummy cards can be separated and used for this purpose). In groups of three to four, students take turns rolling a die (or spinning a number wheel, if dice are prohibited in the school) and advancing a token the indicated number of spaces. A player who lands on a metal space draws a card from the anion pile and makes a compound out of the metal/anion combination (i.e., the space the student landed on and the card drawn). Correspondingly, if a student lands on a nonmetal space, a card is drawn from the cation pile and the student makes a compound out of the nonmetal/cation combination and writes down the correct name and formula for the compound formed. If the player lands on a transition metal or a nonmetal having multiple oxidation states, any valid oxidation state for that element can be used to form a compound. Alternatively, the teacher can make a game board that does not include these elements. Colored plastic discs, figurines, or similar small objects can be used as tokens. Simple game boards can be made on a single sheet of paper; more complicated game boards can be made by drawing squares on multiple sheets of paper and taping them together. The squares can be made in any pattern as long as they connect. Further, polyatomic ions can be included on the game board, and there can be duplicates. The teacher can choose to have students play for a set length of time or until a specified number of compounds has been made. Conclusion These activities are enjoyable ways to actively engage students in processing key concepts related to ionic compound formation and ionic formula writing. Students enjoy the hands-on games as an alternative to repetitive worksheets. Further, the fact that different compounds can be made each time students play helps them to realize that there thousands of unique ionic compounds. These games are also easily differentiated for honors, general, or teamed chemistry classes. The difficulty level depends on whether ions with charges, symbols without charges, or names are used. Using names tends be more difficult for students because they have to determine the correct symbol and charge of each ion before making a compound. These activities can be used as informal or formal assessments. Teachers can circulate and check for student understanding during the activity, make students responsible for checking each other s work, or have students turn in a written record of their efforts for grading. Students can also receive bonus points for correctly challenging another player s incorrect compound. Alternatively, students can play on teams and be equally responsible for the compounds formed. Additionally, the games can be used throughout the year as a review and can be expanded upon as students learn new information. For example, after learning about molar mass, students could play the games and calculate the molar mass of each compound in addition to writing its formula and name. Because they can be played for as little or as long as the teacher desires, they also make great test review activities or substitute plans. 32 The Science Teacher Mollianne G. Logerwell (mgeorge2@gmu.edu) is a teacher in Fairfax County Public Schools and a doctoral candidate at George Mason University in Fairfax, Virginia; Donna R. Sterling (dsterlin@ gmu.edu) is professor of science education at George Mason Uni- p27-33logerwell.indd 32 11/16/ :54:33 AM

7 Fun with Ionic Compounds FIGURE 6 Examples of game boards for Chemistry: The Board Game. December p27-33logerwell.indd 33 11/7/2007 3:52:32 PM