In this lesson students learn how to write Lewis Structures for covalent compounds. This builds on their prior knowledge of how to write Lewis Structures for Ionic Compounds from Unit 3 Lesson 4 and students knowledge of Covalent Compounds from Unit 3 Lesson 6.
Within this lesson I use several resources:
To engage students in the lesson I give them an opportunity to review three concepts which are found on the first seven slides of the PowerPoint. Students are expected to fill in answers at the top of their Unit 3 Lecture 3 Notes Graphic Organizer.
In this part of the lesson I teach students how to perform Lewis Dot Structures for covalent bonds.
To reinforce the idea of Lewis Dot Structures I have students perform whiteboard practice with their partners.
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.
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.
Here are two examples of common student mistakes:
In this first example lewis-mistakes1.JPG.the students did not have 8 valence electrons around Sulfur.
In this second example lewis-mistake-2.JPG the students had too many valence electrons around Sulfur and only used 22 total electrons instead of 24.
As a second way to reinforce Lewis Structures I have students perform a making molecule activity.
For this activity I give one model set to each pair of students. Student then fill in their activity paper by performing several steps:
To begin the activity I go over the directions with the students and do the first example with them. I then give them time to work through the different compounds. As student groups complete each compound I go over the answers. Here is a video showing how I do this.
This is a copy of one student's filled in activity. This student did the work correctly except for naming of the last molecule, phosphate ion. This year I did not teach my students polyatomic ions so I let the naming using prefixes (phoshorous tetraoxide) slide rather than using the proper ion name.
For the final part of this lesson students perform a Lewis Structure Practice Worksheet. If they have time after completing their modeling molecules practice I have them start the paper in class, but they then finish for homework.
I stamp the homework for completion when they come to class the following day and review using the Answer Key.
After all of the practice in class most students do well on the homework. The biggest mistakes continue to be completing using the number of electrons and making sure each atom has 8 electrons, except Hydrogen that has 2. This is especially true when students need to use double or triple bonds to satisfy the octet rule!