When Should I Start Molecular Modeling? Now!

The Next Generation Science Standards aren’t beating around the bush.  Could they make it any more obvious that they want me to use models?  The performance expectations at every grade band expect kids to “develop a model” and “use a model” to prove their understanding of concepts.  I spotted these references to modeling over and over again as I studied the standards.  Surprised by the repetitive use of this word, I compiled a list of what NGSS considers a model.  According to NGSS, models include:

• Flowcharts
• Diagrams
• Drawings
• Pictures
• Digital representations
• Simulations
• Computer visualizations
• Molecular level drawings

What’s my take on NGSS and modeling?  The bottom line is that in every lesson that I teach, my students need to draw pictures of particles.  They need to think about what particles look like, how they interact, how they are pulled apart during physical changes and chemical changes, and consider attractions that occur between them.

NGSS worries many teachers because successful implementation means that some content must be lost.  For AP Chemistry teachers, NGSS poses a concern because loss of content in first year chemistry means that more instruction (and therefore more time) is needed to teach content at the AP level.  However, when it comes to modeling, we should hear AP Chemistry teachers doing some hooting and hollering.  Particle modelling fits in perfectly with the massive changes made to the 2014 AP Chemistry exam.  In every learning objective of the AP Chemistry exam, the College Board included wording that required students to understand chemistry at the particulate level.  AP Chemistry students are now expected to:

• Draw symbolic representations
• Draw particulate representations
• Use aspects of particulate models (particle spacing, motion, and forces of attraction)
• Draw and interpret representations
• Draw diagrams of molecules
• Translate a symbolic depiction at the particulate level

Sound familiar?  Yep.  The College Board expects students to demonstrate the same expertise in particle modeling as NGSS.  So when’s a good time make first year chemistry students draw pictures of particles?  NOW!  Do it now.  You can easily adapt existing curriculum by adding in a question or two about particles pictures.  

Student 1: Predicted particles in aqueous solutions

Here’s an example of how I adapted a lab to include molecular modeling. Recently my accelerated chemistry students learned about predicting precipitates in double replacement reactions.  In terms of background knowledge, they understood from a previous experiment that ionic compounds dissociate upon dissolving in water.  At the start of this qualitative lab, I demonstrated a chemical reaction that produced a precipitate.  My students watched as I dissolved solid sodium chloride into one beaker of water and solid silver nitrate into a second beaker of water.  My students observed that the solids dissolved to make aqueous solutions.  To bring in particle modeling, I added a few questions that asked students to predict what the dissolved compounds looked like on a particulate level.  

Student 1: Predicted product of DR reaction

After they drew their predictions, I had them watch carefully as the two solutions were combined.  The production of a white cloudy precipitate surprised them.  I asked them to draw what they thought happened on a particulate level.  Keep in mind that they had no previous experience with precipitates or double replacement reactions.  Some of their pictures were absolutely crazy (and by crazy I mean tragically wrong.)  

Student 2; A different interpretation of the aqueous solutions

At the end of the lab I gave students the same particle pictures to complete.  They showed mastery the second time around.  Don’t be afraid to have kids make predictions about the unknown.  By the completion of the lab, students gained superior knowledge about how particles interact in double replacement reactions. The idea is simply to get kids thinking and talking about particles.  

Student 2: Predicting what happened when a precipitate formed.

 

Draw on paper, draw on white boards, draw on an iPad. Just get them to start drawing particles.

Atoms in an Uproar Lab- Predicting Precipitates in DR Reactions