1. Draw Lewis structures to show the arrangement of valence electrons among atoms in molecules and polyatomic ions; explain the difference between single, double, and triple covalent bonds.
2. Predict the shape of a molecule using VSEPR theory.
Lewis dot and line structures are part of the language of chemistry and are important for students to be able to be fluent in the language of chemistry.
Here is one teaching video to introduce the subject. It's 20 minutes, but it's a good overview -- and, dude, this narrator is enthusiastic!
Here is a very simple worksheet. It could be used to teach Lewis structures -- you could project the image on an overhead projector to teach the structures. You may want to switch back and forth from notes to this page during your lesson.
One pair of electrons being shared is called a single bond and is drawn with a single line -- for example, H-H. Two pairs (or four) electrons being shared is called a double bond and is drawn with two parallel lines. An example is O2. Three pairs (or six) electrons being shared is called a triple bond and is drawn with three parallel lines. An example is N2.
Here is another video talking about Lewis structures and VSEPR theory. The acronym VSEPR stands for Valence Shell Electron Pair Repulsion and helps to determine the 3-dimensional structure of a molecule whereas the Lewis structure is 2-dimensional.
The theory is that the molecule's shape will decrease the interactions of the valence electrons. Because they are negatively charged they repel, and the molecule shape is to maintain the bonds but keep those electrons as far away from each other as possible.
Whatever shape the molecule takes, it is considered to be stable in this configuration because it minimizes the interactions of the valence electrons. I'll talk about that more when I cover energy and potential energy diagrams in another post.
Here is a video talking about VSEPR theory -- it's longer (about 20 minutes):
I purchased a set of Styrofoam spheres at a local craft shop (sewing stores might have them as well) for demonstration with toothpicks. I was able to purchase the Styrofoam balls in both larger and smaller sizes, so I was able to use the larger sphere as a central atom and the smaller Styrofoam balls as the attachments.
Here is a quick (short) lab handout:
This lab is a little longer, but the chart is handy:
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For other lab ideas, check out my lab book "Chemistry on a Budget" at amazon.com:
Each lab is presented with two possible report formats -- both with the same procedure -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This was to give the teacher the option of what type of report is desired!
Have a good week!