In this lesson students learn how to determine the shape for covalent compounds using VSEPR theory. This builds on students' prior knowledge of how to write Lewis Structures for covalent compounds from Unit 3 lesson 7.
Within this lesson I use several resources:
To begin the lesson and review concepts from the previous lesson I have students perform a quick Lewis Structure question with a partner on a piece of paper or whiteboard. For this class I had them perform the lewis structure for water.
Here is a picture of one group's responses.
After students complete the question and I make sure that they have done it correctly I talk to them about how we will be moving from 2-D lewis structures to 3-D shapes of molecules today.
During this portion of the lesson I present notes related to VSEPR. The notes include:
The notes I present are found on slides 1-11 of the PowerPoint and students fill in their notes on the first page and a half of partially empty slides. This is a copy of one student's filled in notes.
While teaching the content I make sure to stress to students to only look at the CENTRAL atom to determine the shape.
Here is a video of my explanation of the Trigonal Pyrimidal shape with students.
I have students perform these four questions of varied complexity to give them an opportunity to practice different types of shapes with various polarities.
I present the questions one at a time. I give students time to work on the example and go over the answers with them as they complete each question.
To help students I remind them to look back at their notes and make sure to look at the CENTRAL atom to determine the shape.
If students get done quickly I have them also add in the bond angles for each question.
This is a copy of one student's notes with the answers to the practice questions on the bottom of the second page.
In this portion of the lesson I give students time to practice what they have learned by doing a VSEPR Lab.
Students work with a partner using a molecular model kit.
In the lab students do the following:
Before students start the lab I go over the directions with students and point out that each ball color represents different atoms. I also remind students to look back at their notes or on the first page to help with shapes, angles, and polarity.
As students are working I walk around and help them out with making the molecules and make sure that they are working with their partners.
I also periodically go over some of the examples with students on the document camera. This is a video where I go over an example with students.
Here is a copy of one student's completed lab.
As a last way to go over shapes with students in class I lead students in VSEPR whiteboard practice.
I have students work in pairs and each pair needs one whiteboard, one dry erase marker, and one dry eraser. I have students work with partners to encourage them to discuss why they think that a certain answer is correct. I periodically remind them to switch partners in terms of who is doing the writing throughout the whiteboard session.
This is the PowerPoint I use. Note that there are many different types of examples with varied complexity to help ensure that all students are learning the shapes.
1. I put up a problem on the PowerPoint and then have students hold up their answers.
2. I either give thumbs up or down and if they get it incorrect they should retry.
3. After most students answer I go onto the next answer. If it is one that many get wrong I go over why the correct answer is correct either by myself explaining or having a student explain how they determined the answer.
This takes students some time but overall they did well with the whiteboards after having done the other two elaborate sections. Again the most common mistakes are students getting confused about looking at the central atom to determine the number of bonded and lone pairs and students getting the incorrect Lewis Structure and therefore the incorrect shape.
For more information on how I use whiteboards, refer to my reflection on Student Ownership and Whiteboards in my lesson Metallic and Covalent Bonds Formation and Naming.
For homework I have students perform practice questions on a VSEPR worksheet.
I stamp the homework for completion the following class and go over using my answer key.
For the homework students do fairly well with the most common mistakes being incorrect Lewis structures which then relate to incorrect shapes, etc.