Lesson Plan 1: Molecular Geometry
Objective: Students will be able to describe the 3D shape of real simple molecules using VSEPR theory.
- Students will be able to name the molecule and electron geometries for molecules with up to six atoms surrounding a central atom.
- Students will be able to recognize the differences between molecule and electron geometries and explain this using VSEPR theory.
Engage:
- Teacher tells the students that their challenge problem today is to figure out the shape of nitrosyl fluroide (NOF). To do this, the teacher asks students to first draw the lewis structure of NOF individually (Before this lesson, students should already be able to draw lewis structures of molecules.) Teacher monitors and selects students to share. As a whole class, students discuss the possible/correct lewis structure of NOF and use that to predict the shape of NOF. Students draw an initial model of the shape of NOF.
Explore:
- Students will head to a computer lab to use the Molecule Shapes Simulation. Students will be instructed to go to the PhET website and open the Molecule Shapes simulation. Students will identify the molecular geometry, and electron geometry for all 13 cases using the number of single bond and lone pairs indicated in the table. Students will also draw a sketch for each case and label the bond angles in the drawings. Figure 1 shows the data table that will be given to students. Figure 2 shows a sample data table (Note: Students will hand draw the sketches for their data tables.) Students will work individually or in pairs depending on the number of computers available.
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| Figure 1: Data Table for Molecule Shape |
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| Figure 2: Sample Data Table for Molecule Shape |
Explain: (Same time as explore)
- Students will fill out the data table chart provided. Then students will answer the following questions:
- What is the difference between "molecular geometry" and "electron geometry"?
- What general patterns exist for identifying the molecular geometry of a molecule?
- What general patterns exist for identifying the electron geometry of a molecule?
- The goal is for students to name molecule and electron geometries for molecule with up to six electron groups surrounding a central atom and recognize the difference between molecular and electron geometry.
Evaluate:
- Students will revise their model using what they learned from the simulation to come up with an appropriate shape for NOF. The teacher can provide hints and guiding questions.
Explore:
- Students will read handouts regarding VSEPR theory that discuss the idea that molecular geometry is due to repulsions between electron groups and the idea of how lone pairs affect bond angles. Students will be given four different handouts and jigsaw strategy is used. Students will first read together as a group and come up with two to three sentences to summarize the main points. Then students will gather into new groups with at least one person sharing each of the four handouts. The teacher monitors during this time and selects specific students to share out for each of the four handouts.
Evaluate:
- Students will use what they learned to revise their model of NOF. Teacher will monitor and ask guiding questions. Teacher should focus students on thinking about it in terms of the molecular geometry and incorporate students to use what they learned about VSEPR and the effect of lone pairs on the molecular shape.
Extend/Elaborate:
- Students will share their models in groups of four. Each group will come up with a consensus model. Teacher monitors and selects a few models to share. Teacher shows the models using an Elmo (covering any names) to the whole class and ask the students if they agree/disagree, what they agree/disagree with and why.
Homework/Formative assessment:
- Students answer the following questions:
- Predict the molecular and electron geometry of the following molecules.
- XeF2 (xenon difluoride)
- NH3 (ammonia)
- PCl5 (phosphorous pentachloride)
- Go to http://phet.colorado.edu/en/simulation/molecule-shapes. Use the simulation to check your answer. If it is different from your prediction, explain why that might be the case.
- What is the molecular geometry of water? What is the molecular geometry of carbon dioxide? Explain why they are different even though both molecules are composed of 3 atoms each. (Hint: use VSEPR theory and think about how lone pairs affect molecular shape.)
(*This lesson plan is developed using the idea from Robert Anderson - Molecular Shapes LabName lesson plan found here.)
Lesson Plan 2: Factors that affect the rate of a chemical reaction
Content Learning Objective:
- Overall objective: After students carry out reactions of Alka Seltzer tablets reacting in water and looking through and discussing handouts, students will be able to explain how and why the following factors affect the rate of a reaction: concentration, temperature, surface area and agitation.
- Day 1: Students will be able explain how changing the following factors: increase or decrease temperature, concentration, surface area and stir or no stir a reaction affect the rate of a chemical reaction as they carry out an Alka Seltzer reaction.
- Day 2: Students will be able to explain why changing the following factors: temperature, concentration, surface area and agitation affect the rate of a chemical reaction by looking through and discussing handouts with readings including analogies and draw and write about simulations. Students will be able to use the collision theory to justify why increasing or decreasing the temperature or concentration increases or decreases the rate of a chemical reaction.
Engage:
- Teacher performs clock reaction. A simple home version of the reaction can be used. Teacher shows students two beakers of clear solutions, ask them to write down observations and predict what happens when the solutions are mixed together. Teacher picks on a few students to share and then mixes the two reactions. A change of color should be observed. The time this occurs can be adjusted by adjusting the concentration. (I changed the concentration of iodine.) Teacher then asks students to write down their observations and asks the class what they observed. Teacher repeats this reaction with a more concentrated solution. The time it takes to react should be faster. Teacher asks the students to write down and discuss the similarities and differences between case 1 and case 2 where case 2 uses the more concentrated solution and the reaction occurs faster. Teacher then asks students to draw an initial model showing the two beakers with the mixed solutions attempting to explain what caused the difference in reaction rates (why one turned color faster than the other one). Teacher asks students to brainstorm ideas of factors that could affect reaction rates and write down students ideas on the board.
Explore:
- Teacher tells students that they will explore four of the factors to see how they affect the rate of a chemical reaction. Students investigate the factors by reacting Alka Seltzer tablets in water. Students record observations and the time using a stopwatch in a data tablet provided.
- Temperature: use 1/4 tablet in 100 mL water. perform this reaction using room temperature, hot water by heating water using a hot plate and cold water from ice bath.
- Surface Area: use 1/2 tablet in 100 mL water. perform this reaction by using an uncrushed 1/2 tablet and crushing another one using mortar and pestle.
- Agitation: use 1/2 tablet in 100 mL water. perform this reaction by stirring using a stir bar in one case and not stir in another case.
- Concentration: Teacher shows a video of elephant toothpaste reaction. The concentration of hydrogen peroxide is varied. Students write down observations and discuss how concentration affects the reaction rate.
Explain: (same time as explore)
- Students record time and observations as they perform the Alka Setlzer experiments. Students write four sentences describing how each of the above factor affect the rate of a chemical reaction shown below.
- Question: How does each of the following affect the rate of a reaction?
- Grinding a tablet into powder _____________________________________________.
- Heating up a reaction ____________________________________________________.
- Making a reactant more concentrated______________________________________.
- Quickly stirring the reaction_______________________________________________.
Evaluate:
- Students revise initial model based on what they learned from the experiment and the video. Teacher could give hints and guiding questions that focus students to think about the reaction at a molecular level. This leads to the end of day 1 lesson. The goal at the end of the lesson is for students to understand how each of the factors affect the rate of a chemical reaction and beginning to have an insight of why the cause of this is. Teacher summarizes today's lesson by asking students what could be done to increase the rate of a chemical reaction. Teacher asks students to read the objective together as a class.
- Teacher does a quick recap of what students learned yesterday by asking them what could be done to decrease the rate of a chemical reaction. Teacher transitions to today's lesson by telling students today they will figure out why the factors affect the rate they way they do. Students will be given handouts to go along with this explore. Teacher reads objective with the students. Teacher guides students through the handouts. Drop and read is used where teacher reads and stops then students continue to read the next word or words. Teacher asks students to discuss an analogy for concentration - five people in cafeteria vs. everyone in school in cafeteria - how often do people bump into each other in each case if they were blindfolded and asked to wander around. Teacher shows the reaction and rates simulation for concentration and temperature factor.
Simulations:
Concentration
Reaction: A+BC ---> AB+C
Teacher asks students what type of reaction this is. (single displacement) Teacher shows the simulations with two scenarios. Scenario 1 is for a lower concentration (adding two to three molecules of A and BC). Scenario 2 is for a higher concentration (adding 15+ molecules of each type). Teacher asks students to describe what they observed and ask them to discuss this in terms of how and why concentration affect reaction rate. Teacher then asks students to draw what they observed for each scenario in the spaces provided.
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| Scenario 1: lower concentration |
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| Scenario 2: higher concentration |
Students then answer the following and teacher picks on students to share:
- If we have more molecules moving around, there is a __________ (higher/lower) chance they will bump into each other.
- In which scenario do we observe more reactants converting to products? ___________
- A higher concentration means there are _______ (more/less) molecules present. More molecules lead to _______ (more/less) collisions. More collisions lead to _______ (more/less) bonds breaking and thus _______ (faster/slower) reactions.
Temperature:
Teacher drop and read with students then show the same simulation as above but now varying the temperature factor. Teacher shows two scenarios: one at higher temperature and one at lower temperature by either pressing the heat button or cool button. Students draw what they observe in each scenario. Teacher asks students to describe what they observe and discuss how and why temperature affects the rate of a chemical reaction. Students then answer the following and teacher picks on students to share.
- In which scenario do we observe more reactants converting to products?___________
- If we increase the temperature, the molecules move around ___________ (faster/slower) causing more collisions. More collisions lead to _______ (more/less) bonds breaking and thus _______ (faster/slower) reactions.
- At high temperatures, ______________________________________ because the molecules are ________________________________________________.
- If _____________________________________________________, the rate of reaction will decrease because _________________________________________.
- _____________________________ and ____________________________ both increase the rate of reaction because ________________________________________________and __________________________________________.
Evaluate:
- Students revise their model using what they learned and discussed.Teacher give guidance questions that ask students to incorporate what they just learned using the collision theory and the factors that affect rate to explain why the rate of reaction, the rate the two beakers of solution changed color was different. Teacher monitors as students work individually.
Extend/Elaborate:
- Students share their models in group and come up with a consensus model within their groups. Teacher monitors and pick out a few models to share for whole class discussion. Students explain their model and use their model to explain the clock reaction phenomenon. Teacher asks the rest of the class what they agree or disagree with. Teacher engage students in argument from evidence by asking them to explain and help them reason through what could be the possible factor that affected the rate of the clock reaction.
Homework/Formative Assessment:
Students answer the following questions.
- For what reason do we put leftover food in the refrigerator? Explain.
- Chalk reacts with hydrochloric acid when the two are mixed. Will grinding the chalk into a powder increase, decrease, or do nothing to the rate of this reaction? Explain, giving specific reasons for your answer.
Quiz: Students are given a quiz on the factors that affect the rate of a chemical reaction.
Please leave a comment if you would like all the worksheets used for lesson plan 2.
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