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Total Duration:
91 to 120 Minutes
Materials and Resources:
Materials Located in Attachments:
Worksheet: Dipoles and Bond Polarity pHet Activity
Answer Key: Dipoles and Bond Polarity pHet Activity
Prior to this lesson, students should have some knowledge on periodic trends, specifically electronegativity.
Students should also be comfortable with drawing Lewis structures.
Before:
Have students pick a partner in the classroom and pretend that their partner is their twin sibling. Have students assume that they are nearing their 16th birthday and that their parents are requiring them to share a car.
Have students brainstorm ways that they could share the car. Hold a classroom discussion to identify the different ways the car could be shared. Be sure that the following explanations arise in the discussion:
The car could be shared 50/50 where each sibling gets the car for the same amount of time each week.
The car could be shared based on need so the sibling that has more extracurricular activities or events gets the car for a larger percentage of the time; the car is shared unequally.
One sibling could take complete control of the car and not share at all with the other.
Relate the ways that the twins can share the car to the way two atoms can share (or transfer) electrons. Use the Image of Bond Types from UC Davis ChemWiki for visualization.
If the twins share 50/50 then the car spends equal time with each twin similarly to in a nonpolar covalent bond where electrons are evenly distributed around both (or all) atoms. Emphasize that the prefix co- (in covalent) means to share and give examples such as the co-captain of a team.
If the twins share the car depending on who needs/wants the car the most they are sharing unequally. Since electrons are still being shared this is still a covalent bond, however, the unequal distribution makes the bond polar covalent. Ask students what they know of that has poles and encourage them to think about the north/south poles of the earth. Describe that the earth is polar because it has 2 distinct poles (north and south) and polar covalent bonds are polar because they also have 2 distinct poles (positive and negative).
In the case that one twin takes complete control of the car, discuss the comparative strengths of the twins. The one with the most strength (the most electronegative) will take complete control of the car. This is similar to an ionic bond. Emphasize the "i" in ionic and remind students that generally "i" is selfish so the electrons are being completely taken by one of the atoms and not being shared at all. Encourage students to think of why this is still considered a bond and not called an ionic transfer (the positive and negative charges that result from the transfer attract one another holding the ions together).
During:
Students will complete "Dipoles and Bond Polarity pHet Activity" worksheet located within the attachments section with their partner using the pHet website to develop a rule for determining if a molecule is polar or nonpolar. Be certain to discuss the role and importance of lone pairs of electrons.
Students will be assessed using a Jigsaw Cooperative Learning strategy.
Assign each group a set of questions from the student activity worksheet that they will be responsible for sharing the correct answers with the class. After the individual groups complete the activity the class will come together for a discussion and each group will be responsible for discussing their assigned question(s).
Students will complete Alabama Science in Motion (ASIM) activity Molecular Shape and Polarity using 3-D ball and stick model kits and VSEPR Geometries Chart to determine the shape and polarity of various molecules.
After:
Allow students to individually access the Madison College website to complete the Intermolecular Forces: Review to reinforce calculating number of lone pairs of electrons, bonding pairs of electrons, and molecular geometry to review. To assess student mastery the teacher will actively walk around the room and check individual student work before students leave.
Assessment Strategies
The student will be assessed on their completion of "Dipole and Bond Polarity pHet Activity" worksheet as a group using the jigsaw approach where each group will be responsible for completing the sheet on their own and then sharing the answers to assigned questions with the class.
The student will be assessed on completion of Molecular Shape and Polarity chart from ASIM.
The student will be assessed on individual completion of the Intermolecular Forces: Review from Madison College website by the teacher walking around the room and checking individual progress before students leave.
Acceleration:
Students who are already familiar with polarity and molecular shape can use the pHet activity: Molecule Shapes to look at the bond angles for the different shapes.
Intervention:
Students who do not reach mastery on their individual assessment will be pulled for individual or small group instruction drawing molecules on small dry erase boards and discussing molecular arrangement with the teacher.
View the Special Education resources for
instructional guidance in providing modifications and adaptations
for students with significant cognitive disabilities who qualify for the Alabama Alternate Assessment.