May 2020 | Resource Feature
Modeling Polarity An Exploration of Polar Bears
By Catherine Zavacki and Anjana Iyer
Why teach through movement?
In your classroom, are you just covering content? Or are you also engaging your students in novel and varied learning experiences to enhance comprehension and retain content?
One of the tools in our toolbox that has made the largest impact in our classroom over the past 10 years has been integrating movement activities. Teaching through movement necessitates that students get out of their seats — waking them up, and also focusing their attention on the material. It helps to turn each student into a teacher among their peers, creating a whole-body pathway to understanding and, more importantly, making the information more engaging and fun. An added bonus is that many of the activities may be used as a formative assessment, allowing us to gauge student understanding and modify our lessons as necessary.
Overview of the activities
We have used the activities in this article in our unit on polarity (both bond and molecular) in our high school chemistry classes. The first activity was developed in collaboration with our student teacher, Dr. Chris Sosa. In this activity, the students model the pull of electrons in a bond between two elements, demonstrating covalent bonding. In particular, they practice differentiating between polar and nonpolar bonds. Prior to this activity, the students have already learned about electronegativity and how to calculate a difference in electronegativity (ΔEN). In the second activity, the students apply the information they developed in the first activity to a molecule. These activities are utilized on two different days of the unit.
Students will kinesthetically demonstrate the use of electronegativity in determining covalent bond types.
Prior to this activity, a set of cards must be prepared for a variety of nonmetal elements. After printing the cards, put them in plastic sleeves or laminate them so that students can fill in the information using a dry erase marker.
Element you are bonding with:
Type of bond formed:
|Figure 1. Sample element card.|
- Begin by giving each student an element card and have them fill in the electronegativity value for the element.
- Next, direct the students to stand up and partner with another student in the class. Then have the student pairs fill in the rest of the information on their element card.
- The bond information from all students is compiled in a table on the board, or in a shared Google Document. The column headings should read: Element A, Element B, ΔEN, and Bond Type (as shown in Figure 2). This allows the entire class to see the many types of interactions that resulted from the student partnerships.
Note: If you feel your students will mistake the heading “Element B” for the element “Boron,” feel free to use an alternative column heading such as Element 1 or Element 2.
|Figure 2. Example of the bond information compiled from all students in the class.|
Figure 3. Initial arrangement of student string-and-ball models.
- Next, provide each pair of students with a Styrofoam ball threaded onto a piece of string about 6 feet long. In this model, the string represents the bond between the two elements and the ball represents the electron pair.
- Instruct the students to stand about five feet apart and move their ball along the string to approximately represent the electronegativity difference and the specific type of bond in their example. If the electronegativity difference is nonpolar, the ball would be in the halfway point of the string. If the electronegativity difference is polar, the ball will be moved closer to the more electronegative element. Since they are not yet comparing themselves to other pairs in this step, the balls will be in different locations along the strings of the various student pairs (Figure 3).
- When the students are satisfied with their models, ask all of the pairs of students in the class to arrange themselves in two rows (partners across from each other) so that the models are placed in order of decreasing electronegativity difference.
- Students should recognize two types of bonds:
- If the bond is nonpolar covalent, the ball will be held in the middle of the string, demonstrating equal sharing of electrons.
- If the bond is polar covalent, the ball will be held closer to the more electronegative atom, demonstrating the greater pull and unequal sharing.
- The instructor should lead a discussion to help the students compare their electronegativity difference to the pair next to them, and the location they chose for their ball. Based on their observations, have the students adjust the location of their Styrofoam ball. The students will hopefully see a trend forming: that the stronger the electronegativity difference, the closer the ball is to the element with the higher electronegativity.
- Finally, the students should determine which elements in each of the polar bonds will have partial charges.
Having the students work in pairs gives them the opportunity to collaborate on their initial estimate of where they think the ball should be located. Then, moving into a whole group activity, the students can develop an understanding of the concept by talking through their questions with each other (with the instructor facilitating).
In the next activity, the students are able to reference back to this activity in their discussions. This allows for faster recall when the instructor asks, “Remember standing across from your partner with your string? Why did you place your ball where you did?” Following this activity, take a few days to present lessons on VSEPR. Once students have learned how to do the 3D drawings, they’re ready to perform Activity 2.
Students will model bonds in a compound to determine the overall polarity of a molecule.
To prepare for this activity, create a new set of cards for each molecule and its individual elements (Figure 4). Some examples of the compounds used are: methane (CH4), carbon dioxide (CO2), ammonia (NH3), water (H2O), and hydrogen fluoride (HF).
- Assign a different set of covalent compound cards for each group of 3-4 students. Our students sit in pods; students could also work at their lab tables if your classroom is set up differently.
- In their groups, the students work together to determine the arrangement in which the elements will bond together. If the students prefer, they may use white boards to draw their initial Lewis structure before they arrange their cards on the table.
- Next, the students fill in the first three pieces of information on the element card (element bonding with, electronegativity difference [ΔEN], and bond polarity). If the bond type is polar, students write the respective partial charges on their cards.
After you created your structure: does the molecular polarity stay polar or become nonpolar?
After you created your structure: does the molecular polarity stay polar or become nonpolar?
Figure 4. Sample covalent compound cards for the molecule NH3 (two additional H cards should be used as well).
- Now instruct the students to stand up and “become” the compound. Each student holds one of the element cards and is given the string-and-ball model to represent the bond between it and another element.
- Similar to Activity 1, students are asked to move the ball along the string depending on the electronegativity difference between the bonded elements.
- For NH3, and H2O, there will be lone pairs on the atom. To represent this, another student needs to stand nearby, holding a ball or balloon to represent the lone pair (Figure 5).
- Each group is asked to model their structures for the class and also lead a discussion by drawing their structures on the board and describing the overall molecular polarity. Students should recognize several important concepts:
- If all the bond types around the central atom are nonpolar, the pull should be even and the compound will be non-polar.
- If all the bond types around the central atom are polar, even though the electrons are not equally shared, the central atom experiences equal pull from all sides, canceling the bond dipole and making the molecule nonpolar. If some bond types are polar and others are nonpolar, or if the central atom has a lone pair of electrons, the central atom will experience a dipole, making the molecule polar.
- There are some exceptions to the above rules. For example, in a square planar (or linear with two bonds and three lone pairs), the four bonds are polar and there are lone pairs on the central atom, but the molecule is nonpolar. Therefore, you will need to modify your discussion for the expectations of your class.
|Figure 5. A student group modeling the structure of a water molecule.|
For enrichment, teachers could introduce substances, like ethanol, that have both polar and nonpolar parts. This could lead to interesting discussions about intermolecular forces of attraction.
Throughout each unit of the curriculum, we strive to include both fine and gross motor kinesthetic activities into our lessons. Although computer programs and worksheets have their places in the classroom, having students actively engage their whole bodies in the learning allows them to experience the concept in a novel way. They are able to make emotional and interpersonal connections, all while creating more neurological pathways — resulting in deeper understanding, better retention, and recall.1 When a student asks a question regarding the content, it is significantly easier for them to recall the information from an experience of jumping, spinning, milling around, or linking arms than it is to remember, say, the color of a worksheet!
- Lengel, T and Kuczala, M. The kinesthetic classroom: Teaching and learning through movement; Corwin: Thousand Oaks, California, 2010.
(article cover) Dragon Images/Bigstock.com