Kinetic Theory of Matter

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Objective

As our model of thermal energy has evolved over time, students begin to connect our thinking to the properties of atoms and molecules.

Big Idea

The macroscopic properties of materials (temperature, state, density, etc.) can be explained by its microscopic properties.

Overview

Today's lesson provides opportunities for two key learning goals. First, by probing down to the molecular level, we can connect the microscopic world of particles with macroscopic properties of materials. For example, properties like solidity and temperature can be related back to the actions and interactions of particles. In addition, by considering the strength of the particle interactions ("bond strength" though I'm careful not to introduce that language at this point), we can hint at electrical charges and the forces they produce. As this is the topic of our next unit, this lesson is an excellent transitional lesson from one unit to the next.

In addition to those content ideas, this is a great opportunity for students to express their internalized models of particle interactions.

 

Warmup

15 minutes

The warmup for this lesson has students confronting novel situations.  Though we have not done a problem just like this, the concepts are now well-established and, if students can get past the initial sense of "discomfort," they should be able to solve both of the parts of the warmup problem.

To build a sense of initiative, I ask students to work solo for the first four minutes of the warmup time. After that, if desired, students can consult with either me or a classmate. The four-minute timer is long enough to discourage any students from simply waiting, while also being short enough to prevent a sense of frustration from setting in.  

As part of the discussion, I am transparent about the word "initiative." I want students to see that the act of trying, even when a problem looks unfamiliar, is a skill that can be developed over time. I call that act "initiative" and use it to describe the act of taking steps forward even when one realizes that a task is not obvious. It is my hope that students will begin to recognize those moments and push themselves onward, even if they are unsure of the outcome.

After the four-minute solo time is over, students can collaborate to solve the warmup. After just a few more minutes, I present solutions at the board (see solution part a and solution part b).

 

 

Thinking about Our Thermal Model

15 minutes

I ask students to think about a sample of water in a beaker being heated up by, say, a candle.  I ask them to illustrate - with symbols, words, labels, etc. - where the energy goes with whatever detail they can summon.

Then I prompt them to consider what is happening, water molecule by water molecule.  In other words, how does energy actually, physically, move throughout the sample of water and, eventually, into the beaker and air.

I share these prompts one at a time for students to think about, using a shade feature on the Smartboard to conceal the second prompt until ready.

After 3-4 minutes of this work, I have students turn and talk to classmates to compare answers. After two minutes of sharing, I ask to hear a few of the comments that students found intriguing. I'll collect more thoughts in the next segment of class.

Interactive Notes

25 minutes

Together, we fill out the first page of the Kinetic Theory notes and images.  I ask for qualitative language to describe the bonding, spacing, and movements of the molecules in three states of matter. I probe their understanding of what happens when more energy is added to a substance.

For the remainder of the exercise to work it is imperative that I not describe the nature of the bonds. I ask students to illustrate with solids and liquids "what is happening between the molecules."  I anticipate they'll draw springs, or arrows, or links, and that these drawings will look different between the solid and liquid drawings (pages 2 and 3 of the handout). Though this is my first time ever teaching this lesson, I know that students have had, at the very least, some middle school instruction on the structure and nature of atoms and molecules. All students have also had a rigorous Environmental Science course as 9th-graders, during which they considered the movement of certain kinds of elements and compounds (like Mercury) in ecosystems. In addition, some students have had Chemistry. What I can rely upon, then, is that all students should have some insight into the nature of particles. This exercise allows me to see the differences in understanding without subjecting students to the anxiety of assessment.

After illustrating, students share with one another and then share with the class.  I have students come to board and draw in their models.  After some time, I ask them to adapt their model to gases, based on the bonding, spacing, and movement notes from the first page.

Team Time

25 minutes

As with many open-ended investigations, our "Hot Rocks" investigation has proven difficult to wrap up. Teams have had different questions which, in turn, have different kinds of associated activity: some teams will need to collect new data while some will need to analyze previously collected data. Additionally, because of the nature of the question, some teams will be able to more quickly move towards the creation of a presentation than others.

I provide this last segment of time for teams to self-assess and work towards the completion of their investigation. My role is to circulate and help student teams get what they need and stay on task. I also need to demonstrate some flexibility as I assist each team with their unique needs. This is the last class time that will be dedicated to this investigation.