Introduction to Gases in our Atmosphere and the Kinetic Molecular Theory

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Objective

Student will be able to explain the importance of gases in our atmosphere, how gases behave according to the kinetic molecular theory, and how gases are measured in terms of temperature and pressure. They will demonstrate their understanding through performing a reading, doing activities, taking notes, and performing practice questions.

Big Idea

Gases make up our atmosphere and scientists characterize gas behavior using the Kinetic Molecular Theory.

Introduction

In this lesson students are introduced to the concept of Earth's atmosphere through a reading, and then taught more details about the kinetic molecular theory and gas behavior through notes, videos, demonstrations, and practice questions.

  • This is the first lesson of a unit that does not align with any specific NGSS Performance Expectation; however, it does align with the old California State Standards.  Additionally, I feel that understanding gas laws and the basics of earth's atmosphere are important for students to know and is a topic that is interesting and fun for students.
  • This lesson aligns with the Next Generation Science and Engineering Practice 2: Developing and Using Models.  It does so because students are given the opportunity to model how gases behave through several activities.
  • This lesson also aligns with the Next Generation Science and Engineering Practice 5: Using Mathematics and Computational Thinking.  It does so because students are required to use math to solve equations related to temperature and pressure.
  • This lesson aligns with the Next Generation Crosscutting Concept 3: Scale, Proportion, and Quantity.  It does so because students are challenged to think about gases, despite the fact that they cannot see them.

For this lesson there are several resources needed:

1. For popcorn reading I use a bouncy ball.

2. For the syringe activity I provide a large syringe (with no needle) for every 2-3 students.

3. For the diffusion demonstration I use two large graduated cylinders.  One of them contains ice cold water while the other contains nearly boiling hot water.  I also use food coloring.

Introduction to the Unit

30 minutes

To begin the unit I have students perform a reading about earth's atmosphere and answer several questions as they read. 

I like to have my students practice reading out-loud so I use Popcorn reading as a strategy.  (For details about how this works see my reflection on Popcorn Reading in my Ionic, Covalent, and Metallic Bonds Lesson).

I chose this reading because it gives the basics of the atmosphere in terms of its layers, the importance of the various gases, and how scientists can measure parts of the atmosphere.

Before we begin reading I have students take several moments to read over the questions on the back of the reading so that they will know what they are responsible for answering at the end of the reading.

I then begin reading the first paragraph and then pass the ball onto another student who continues to read.

When the class is done reading the article I give them about 5 minutes to answer the questions on their own.  I then tell them that if they are stuck with any of the answers that they should get help from their table groups and I give them another 3 or so minutes.

Here are two copies of students filled in answers to the reading (Earths atmosphere student example #1) and (Earths atmosphere student example #2).

Notice how in example #2 the student highlighted information as she read to help find the answers to the questions.

Engage Part I

15 minutes

To get students to start to think about gases I have them do an activity using syringes and then I create an event and challenge them to create a model of the diffusion that occurred. 

I first start with the syringe activity and show students the first slide of the lesson's PowerPoint and have them look at the top of their Demos PaperI like this activity because it gets students thinking about how pressure is related to air. 

  • I pass out the syringes to the students (2 per group table) and introduce the activity to students as can be seen in this Video.
  • I then have students play with the syringes and think about the questions on their paper.  After students have had time to think and answer the questions (about 5 minutes) I stop the class and have them share out their ideas. This Video is an example of the questioning I used with one class.

I then have students begin to think about diffusion by having students come up with a model of the smell of a cut up lemon moves around the classroom. I show students the second slide of the PowerPoint and have them look at the bottom of the first page of their Demos Paper.

I instruct students to predict and model what happens when an lemon is cut open and give them some time to work. After students complete their models, I stand in the middle of the classroom to cut open a lemon, having told students to raise their hands when they first smell the lemon. (If I forget to bring a lemon I also use air freshener or you can even use spray cleaner.)

  • For the most part, students closest to me smell it first. Usually students towards the outside of the room can't smell it at all. We discuss how the particles move in a random way and mix with the air so they are less concentrated by the time they get to students further away.

This is an example of one student's responses to the questions for the activities.

Explain/Elaborate Part I

30 minutes

Once students have started to think about gasses and pressure through the syringe activity I then go into notes with students. 

The notes are found on the PowerPoint on slides 4-15.  While I present the information students fill in their notes and perform practice questions on the first page of their Notes Graphic Organizer.

I begin this section of the lesson by introducing the Kinetic Molecular Theory in terms of gases' size, motion, and energy (slides 4-6).

I then introduce pressure and explain how there are many units to measure pressure (slides 7-8).  I also have students practice converting between the different units (slides 9-12).  Many students get confused with pressure conversions so I need to make sure to explain to them that all of the units on the table on slide 8 are equivalent to each other so can be set equal to each other in a conversion factor.

I also remind students about temperature (which we already learned about first semester) and how to convert between Celsius and Kelvin (slides 13-15).

This is a copy of one student's filled in notes for this section.

Engage Part II

10 minutes

To break up the notes I stop students and have a second demonstration to engage students into the next portion of the lesson.  This portion of the lesson is on slide 16 of the PowerPoint and students answer questions on the back of their Demos Paper.

The goal of this demonstration is for students to understand that substances will move slower when the temperature is cold, and faster when its hot.

  • I begin the demonstration by showing students the two 500mL graduated cylinders at the front of the classroom, one filled with hot water and the other with cold water.   I get the hot water from boiling 500mL on a hot plate at the beginning of class and have ice water in a 500mL beaker in my refrigerator.
  • I ask students to predict what they think will happen when a drop of food coloring is placed into each of the graduated cylinders (question #1).
  • After students have had a chance to write down their predictions I quickly put a drop of food coloring into each and have them write down their observations of what is happening at the visual level (question #2).
  • I then have students think about what is occurring at the particle level and have them come up with a model (question #3).  I help students out by drawing a model on the board.
  • Finally I have students think about what they think the graduated cylinders will look like by the end of class (question #4).
    • For this question some of the students think that they will look the same, but for the wrong reason.  They answer that they will look the same because they will have the same temperature.  I make sure to show them that they end up looking the same but then have them feel the cylinders and they can feel that the hot water is still much warmer than the cold water.  This is a Picture of the graduated cylinders at the end of one class.

This is a movie of how I do this demonstration in my class.

Here are two examples of students filled in demo papers with answers to this demonstration at the top of the second page.

Student example #1

Student example #2

Explain/Elaborate Part II

20 minutes

In this section of the notes I explain to students the concepts of diffusion and effusion.  These notes are found on slides 18 to 22 of the PowerPoint and students fill in the notes on the second page of their Notes Graphic Organizer

I begin by explaining how for both effusion and diffusion that the size of gas particles and temperature effect how fast they move (slides 17-18).  When going over slide 18 I give students the molar mass of the different molecules shows so they can see the relationship between relative speed and mass.

I then talk about effusion and stress how its the escape of gas.  I use the example of a birthday balloon slowly deflating over time (slide 19).

I then go over diffusion and explain how is simply the movement of gas around a room similar to the example at the beginning of class with cutting open a lemon or the smell of air freshener around the room (slide 20).

I show students the movie Diffusion of Bromine Vapor and have them answer several questions (slide 20-21). 

I like this video because it gives a visual to students of how gases move.

Finally I have students perform two practice questions (slide 22).  Again, it is helpful to remind students of how to determine molar mass using their Periodic Tables.

This is a copy of one student's filled in notes with the example problems.

Evaluate

10 minutes

For the last section of this lesson I have student revisit their model of cutting open a lemon and then begin their homework.

  1. First I have students revisit their model of the lemon at the bottom of the second page of their activity paper.
  2. Students draw a new model and then discuss if it has changed at all from their previous model. 
  3. This is an example of one student's new model at the bottom of the second page of their Unit 7 lec 1 activities paper.  Notice how in this model the student reflects on how the particles become less concentrated as they move from the lemon and also how the model goes from showing waves of scent to particles.
  4. I then have students work on their Unit 7 Lecture 1 Homework which I have them complete at home, stamp for completion the following day, and review using the answer key. 
  5. The biggest confusions that students had with the homework was correctly converting between pressure units (questions 6 and 7) and deciding which particles will effuse or diffuse the fastest based on mass (questions 11 and 14).
  6. Here is one example of a student's homework.  I like how you can see where the student made changes to her answers after going over the answers as a class.