Lewis Take II and Density????

What am I doing to help kids achieve?

How do I know when they are there?

What is the evidence?

  First, I would like to thank all those who commented on my last blog. For the record, I was wrong. Initially I looked at Linus Paulings early papers as he worked on electronegativity. Much of the work focused on connecting the concept to bond energy. There were some great comments posted to the blog. Probably one of the best was explaining how the concept of electronegativity presents a model for bonds. It is not an observable quantity. This really helped me explain it better to my students. As the commentor posted, all models have limitations. Second, the person commented that in Linus Pauling's General Chemistry book published in 1970 (Dover Publishing) that he does indeed talk about the differences in electronegativity to discuss a type of ionic and covalent character. I stand corrected.

  Another person also commented about a paper by Cooper and Klymkowsky that focus on students struggles with Lewis dot structures. Ironically, I used it writing the Lewis structure activity. I found the same thing the authors found...students struggle with the rules. Cooper and Klymkowsky propose to look at stability instead of talking about "wanting an octet". So here is the idea and feel free to check it out. Take any Lewis dot structure. Add up all of the heats of formations and add up all of the differences in electronegativities. Now redraw the Lewis dot structure in a way that follows the octet rule but is the wrong Lewis dot structure. If you add up all the heats of formation and the sum of all the changes in electronegativities between the bonds, the sum of the enthalpy is higher (less negative) than the other correct structure and the sum of the electronegativity is lower than the correct structure. Pretty interesting....a table of electronegativities can help students determine the correct structure and can be used to talk about a stable bonding environment. Check it out and let me know what you think....

  Here is another crazy idea. This year in chemistry we have not done "density" yet. Most of our students had this as Freshman. We decided that it is proportional reasoning and is similar to the proportional reasoning used in mole calculations. I have taught density probably 101 different ways. Starting Tuesday, it will be 102. I am using Chad Bridle's activity from Grand Valley called "The Murky Mystery of Matter Measurement". It uses the idea of finding the density of beads. It occurred to me that the beads probably (hopefully) will help students visualize the particulate as well. As always...if anyone has any ideas or comments, don't hesitate to keep them coming. It is always nice to have help on this journey we call teaching and learning....

The graphic included is of a text called General Chemistry by Linus Pauling. A reprint of that text can be found on Amazon.com.