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Writing for ChemEdX

Hi all! It feels like it has been a long time since I have posted here (because is has been!). It is not because I grew weary of posting about my classroom (never!), I just started writing for ChemEdX in the past year and all of my new ideas have been posted there!

I will try to continue to add to this blog and link my ChemEdX articles, I just need to play a little bit of catch-up.

If you have not checked out ChemEdX, go there immediately! It is an amazing place full of awesome chemistry teachers sharing about their classrooms! What could be better?

Here is a link to my blog on ChemEdX, but trust me, you want to read everything else on there too.

A few things to stay tuned for on this blog:

  • My move to a deskless classroom next year!
  • My experiences and resources after a year of teaching 9th grade physical science
  • My experiences teaching in a co-taught classroom

Honors Chemistry Learning Targets

I just updated my general chemistry learning targets to this year’s edit and I thought I would post my honors chemistry targets as well. I picked up this prep for the first time this year so I’m sure these targets will undergo some serious edits throughout the year.

I also noticed that I switch from the language “learning goals” to “learning targets” from the last time I posted. This was due to an effort in my previous district to have everyone using the same language. I actually prefer the word “goals” for students but teachers seem to be more familiar with “targets.”

Unit 1: Physical Properties of Matter

1.1 – I can represent elements, compounds and molecules as “hard spheres” in particle models

1.2 – I can apply the Law of Conservation of Mass to situations involving chemical and physical change

1.3 – I can define mass, volume, and density in terms of a substance’s particles using appropriate units

1.4 – I can apply the relationship between mass, volume and density to solve quantitative problems
Unit 2: Energy and States of Matter Part 1

2.1 – I can represent the characteristics (motion, arrangement, and attraction) of particles in different states of matter

2.2 – I can relate the temperature of a substance to the average kinetic energy of its particles

2.3 – I can relate the pressure a gas exerts to the number of collisions its particles make with a surface

2.4 – I can determine the partial pressure of a particular gas in a mixture

2.5 – I can predict the effect of changing the pressure, volume, or temperature of a gas on other variables when two variables are held constant

2.6 – I can predict the effect of changing the pressure, volume, or temperature of a gas on other variables when one variable is held constant

Unit 3: Energy and States of Matter Part 2

3.1 – I can describe the energy transfer between a system and its surrounding during a phase or temperature change as endothermic or exothermic

3.2 – I can recognize that energy can be stored in an object or system as thermal energy or phase energy

3.3 – I can draw an energy bar graph to account for energy transfer and storage in all sorts of changes

3.4 – I can identify phases present and the various phase change temperatures for substances from a heating/cooling curve

3.5 – I can state the physical meaning of heat of fusion, heat of vaporization, and heat capacity

3.6 – I can calculate the quantity of energy transferred, mass of substance involved, or temperature change for a system that has undergone a temperature change

3.7 – I can calculate the quantity of energy transferred, mass of substance involved, or temperature change for a system that has undergone a phase change
Unit 4: Describing Substances

4.1 – I can distinguish among elements, compounds, pure substances, and mixtures

4.2 – I can distinguish between solutions, suspensions and colloids and describe the unique properties of each

4.3 – I can predict the effects of various factors on rates of dissolution

4.4 – I can determine how the boiling point and freezing points of a solution differ from those of a pure substance

4.5 – I can state features of Dalton’s model of the atom
Unit 5: Particles with Internal Structure

5.1 – I can explain how ions are formed and how they combine to form neutral substances

5.2 – I can determine the oxidation numbers for various elements in a compound

5.3 – I can distinguish between metals and nonmetals and describe the unique properties of each

5.4 – I can distinguish between ionic, molecular, and atomic solids and describe the unique properties of each

5.5 – I can name and write formulas for ionic compounds

5.6 – I can name and write formulas for molecular compounds

5.7 – I can determine whether a substance is ionic or molecular from the name or formula of a substance

Unit 6: Chemical Reactions: Particles and Energy

6.1 – I can identify evidence of chemical reactions in terms of macroscopic observations

6.2 – I can write balanced chemical equations including net ionic equations

6.3 – I can explain that coefficients in a chemical equation describe the quantities of substances involved and subscripts describe the number of atoms involved

6.4 – I can identify basic patterns in the way substances react (reaction types) and use them to predict products

6.5 – I can predict the solubility of products of a chemical reaction based on chemical properties

6.6 – I can describe endothermic and exothermic reactions in terms of storage or release of chemical potential energy

6.7 – I can calculate the enthalpy for a given chemical reaction using Hess’s Law

6.8 – I can use enthalpy, entropy and free energy to predict if a reaction will occur
Unit 7: Counting Particles Too Small to See

7.1 – I can convert between mass and moles of an element or compound

7.2 – I can convert between the number of particles and moles of an element or compound

7.3 – I can relate the molar concentration (molarity) of a solution to the number of moles and volume of the solution

7.4 – I can determine the empirical formula of a compound given the mass or percent composition

7.5 – I can determine the molecular formula of a compound given the mass or percent composition and molar mass

7.6 – I can calculate the rate of effusion for a gas
Unit 8: Stoichiometry

8.1 – I can calculate the number of moles of reactants and products in a chemical reaction from the number of moles of one reactant or product

8.2 – I can determine the theoretical yield for a reaction

8.3 – I can determine the percent yield for a reaction

8.4 – I can determine the limiting reactant in a chemical reaction

8.5 – I can use the ideal gas law equation to determine the number of moles in a sample of gas not at standard conditions
Unit 9: Oxidation- Reduction Reactions

9.1 – I can identify redox reactions as a type of chemical reaction

9.2 – I can assign oxidation numbers to elements in a redox reaction

9.3 – I can write oxidation and reduction half reactions

9.4 – I can balance redox equations
Unit 10: Acids and Bases
10.1 – I can distinguish between acids and bases and describe the ions they form

10.2 – I can write the balanced equation for a proton-transfer reaction

10.3 – I can define and calculate pH as the negative log concentration of hydronium ions in a solution

10.4 – I can write the names and formulas of common binary acids and oxyacids

10.5 – I can predict the products of a neutralization reaction between a strong acid and strong base

10.6 – I can distinguish between strong acids and bases and weak acids and bases

10.7 – I can write net ionic equations for reactions between strong acids/bases and weak acids/bases
Unit 11: The Nucleus

11.1 – I can draw the models of the atom proposed by Thomson and Rutherford.

11.2 – I can state the location in the atom, the charge, and the relative mass of protons and neutrons

11.3 – I can distinguish between the atomic number, mass number and atomic mass for an element

11.4 – I can calculate the average molar mass of an element using mass spectrometry data

11.5 – I can describe the three types of nuclear radiation in terms of mass, charge, penetrating power, ionization potential and biological hazard

11.6 – I can write a balanced equation for a nuclear decay reaction

11.7 – I can use the half-life equation to solve for the fraction of original material remaining,
elapsed time, or half-life

11.8 – I can analyze the pros and cons of nuclear technology including fission and fusion applications
Unit 12: Beyond the Nucleus

12.1 – I can draw the model of the atom proposed by Bohr

12.2 – I can represent the first 20 elements on the periodic table using men-in-well diagrams

12.3 – I can account for periodic trends in ionization energy, atomic radius and electronegativity

12.4 – I can represent the first 20 elements on the periodic table using electron configurations

12.5 – I can visualize the 3D molecular geometry of simple molecular compounds

12.6 – I can construct Lewis structures for simple molecular compounds

12.7 – I can determine whether a simple molecular compound is polar or non-polar

12.8 – I can identify the intermolecular attractions at work in a substance and their implications on material properties
Unit 13: Reaction Kinetics

13.1 – I can use collision theory to identify and explain factors that influence reaction rate

13.2 – I can explain the terms “activation energy” and “catalyst” and their relationship to reaction rates

13.3 – I can write the rate law for a simple reaction based on experimental data

13.4 – I can define equilibrium in terms of the reaction rates of a reversible reaction

13.5 – I can identify and explain factors that cause equilibrium to shift

Laboratory Skills

Lab.1 – I can conduct and clean up laboratory experiments properly and safely

Lab.2 – I can identify the hypothesis to be tested, phenomenon to be investigated, or the problem to be solved

Lab.3 – I can document experimental procedures clearly and completely

Lab.4 – I can record observations and experimental data neatly and accurately

Lab.5 – I can justify conclusions using experimental evidence
Communication Skills

Com.1 – I can communicate precision of measurements and calculations using significant figures

Com.2 – I can analyze the slope and y-intercept for a line of best fit to explain a scientific relationship.

Com.3 – I can convert between units of measurement

Chemistry, more like cheMYSTERY to me! -Dalton’s Model

We left off in this model building series with the very meaty Unit 3 on heat and temperature. While I love Unit 3, it is mentally taxing on my students and myself. Unit 4 is a welcomed break.

Here is where we left off in our model:

  • If temperature is a measure of the “hotness” of a system then heat is the quantity of “hotness”
  • Heat can go into a system (endothermic) or flow out of a system (exothermic)
  • Heat can be stored in 2 energy accounts: thermal and phase
  • A change in thermal energy means a change in particle speed and is shown by a slope on a temperature-time graph
  • A change in phase energy means a change in particle spacing and is shown by a plateau on a temperature-time graph
  • The quantity of heat transferred during a temperature change can be calculated using the mass, specific heat and change in temperature for the system
  • The quantity of heat transferred during a phase change can be calculated using the mass and heat of fusion or vaporization for the system

I start Unit 4 with a challenge…

Mixture Separation Challenge 

To kick off this unit, I give each group of students an Erlenmeyer flask with a mystery mixture in it.


I have the students observe the mixture and try to figure out what 3 particles it is made of. Sand and salt are easy to identify but the iron filings give them trouble. When I hold a magnet to the flask, at least one student in the class is able to identify the iron. I then set the groups loose to come up with a plan and materials list to separate the mixture. When their plan is approved, the students get to work. I did not have time this year to let students boil the water off their salt so they just focused on recovering the sand and iron filings.


I make it a competition and award a small prize to the group with cleanest separation. This year, in honor of Dinovember, the winning groups received dinosaur shaped fruit snacks.

I also talk about distillation here and usually relate it to that person everyone knows who makes moonshine in his garage. Once students understand that physical properties remain the same when particles are physically mixed together, it is time to chemically combine particles.

Making and Breaking a Compound

I start by mixing sulfur powder and iron filings in a test tube and showing students that each substance retains its properties. Then I heat the mixture over a flame. This is best done in a hood since the sulfur gas can be quite noxious. I like to set up my iPevo doc cam so students can see what is happening in the test tube on the SMARTboard. After a few minutes of heating, it is clear that something new has been made. That something new does not have the same properties as the original sulfur and iron. This demonstration is part of the first worksheet for this unit from the Modeling materials. One of the questions requires students to draw particle models of the original mixture and the new compound.

Now that we have made a compound, it is time to see if we can break one apart. Typically, I use a Hoffman apparatus to show the electrolysis of water because you can collect enough gas to show the unique properties of hydrogen and oxygen. This year, a Hoffman apparatus was not available so I had students electrolyze water at their desks with 9-volt batteries. This was not a perfect demonstration but served the purpose of showing that water particles can actually be broken down further. Looks like we just broke apart a compound and our model! I also show the Ring of Truth video on electrolysis of water. This is where I introduce the term “element” and the periodic table. This is also the point in time where my periodic table fell off the wall and attacked me. The element of surprise is real.

Once students have distinguished elements, compounds and mixtures and pure substances I have them practice drawing and classifying a variety of particle diagrams to check their understanding.

Now that we have established that elements can combine to make compounds, we must determine the ratios in which these elements combine.

Avogadro’s Hypothesis

I use the worksheet from the Modeling materials to introduce Avogadro’s hypothesis. As a class, we explore the observations from combining volumes of gases to predict the formulas of various compounds. We also find out from this worksheet that some elements are diatomic.


The problem is, most elements are not found as gases at room temperature. How do we figure out the formulas of other compounds?

Laws of Definite and Multiple Proportions

I also use the worksheet from the Modeling materials to explore the Laws of Definite and Multiple proportions. This worksheet has students explore mass data to conclude that different elements must have different masses. We can then use the mass ratios to determine the formulas of various compounds.


Democritus to Dalton

I wrap up Unit 4 by having students complete the Democritus to Dalton reading on their own and taking a short reading quiz on Google Forms. I no longer have students complete the Dalton’s Playhouse activity because it seemed to confuse students more than help them. That is an activity I would like to redesign for next year though. I always like students to be able to answer the questions, “how do we know?”

Unit 4 is short and sweet but brought some big changes to our model!

Here is what we added to the model so far…

  • All matter is made indestructible particles called atoms.
  • Different types of atoms are called elements.
  • All atoms of the same element are identical. Different elements have different properties.
  • Atoms combine chemically in simple, whole number ratios to make compounds.

From Democritus to Dalton was big leap, but Dalton’s fish hook hypothesis about bonding will not be sticking around for long.



SBG and PowerSchool: They can be friends!

When I started using SBG, the gradebook my district used was not compatible with my grading system so I paid for an ActiveGrade subscription from my own pocket. I posted overall letter grades in the district system but grade details were in ActiveGrade. Students and parents were able to log in and see their grades but the biggest complain I got was, “I don’t like having to look at two gradebooks.” That was a completely valid complaint. As a teacher, I didn’t like having to keep track of two gradebooks.

I moved districts this year and my new district uses PowerSchool. I had no experience with PowerSchool so I asked my Tech Department if it could work with SBG. Luckily my Tech Department is awesome and put in a lot of time with me to get it up and running. I know a lot of districts use PowerSchool so here is a rundown of how you can make PowerSchool work with SBG.

The only catch is, you can’t do this on your own. You need to make friends with your district’s PowerSchool administrator. Once you and your PowerSchool administrator are best buds, you can jump right in!

STEP 1: Get your targets in the system

SBG is centered around your learning targets, so that is where you need to start. Get your PowerSchool administrator a list of your learning targets so he or she can put them into the system. This is where you want to plan ahead because you cannot edit these yourself. Be nice to your tech people and give them everything at once so they don’t have to keep going back in to add things. If your targets are coded, make sure to tell your tech team to include the code in the target description otherwise students will not see it.

STEP 2: Plan your rubric

Your rubric is the scale you use to grade each target. I use a “not yet”, “almost”, “got it” system which translates to “0”, “1”, “2” in my gradebook. You need to have numbers and percentages for PowerSchool to calculate your grade. I use “0%”, “50%” and “100%” respectively. PowerSchool will calculate a final grade across all of your targets using these percentages. If you are a percent mastery grader, you would want to make your mastery level worth 100% and everything else worth 0%. This is something your PowerSchool administrator needs to set up and assign to all of your learning targets.

STEP 3: Set your standard grade calculation method

Finally, something you can do! In your PowerTeacher gradebook, go to the ‘Tools” dropdown menu and click “preferences.” Go to the “standards” tab.


Check the boxes I have checked and set your calculation method. PowerSchool can do mean, weighted mean, median, highest, mode and most recent. Click “OK.” I don’t use higher level standards or “power standards” but you could set that up as well.

STEP 4: Add your targets to the grading quarter

This is the easiest step to forget and PowerSchool will not calculate final grades without it. In your PowerTeacher gradebook, click the “Grade Setup” tab and double-click the grading quarter you are currently in to bring up the settings.

GP Setup

Click the radio button for “Term Weights/Standards Weights” and then click “Add Standards.” This will bring up a dialog box where you can check all the targets you want to be calculated into the final grade. You can always go back and change this later.

STEP 5: Enter Grades!

You now have a gradebook. Yay! It’s time to meet your new best friend, the standards drawer. In your PowerTeacher gradebook, go to your “Assignments” tab and create a new assignment.

new assignment

Make sure your assignment is out of zero points and use the “standards” tab to tie learning targets to the assignment. Save the assignment and go to your “Scoresheet” tab.

standards drawer

You will notice a box with an “S” in it appears with your assignment. Click that box to open your standards drawer. This is where you can put in your grades for each learning target for your assignments. NOTE: The box turns green when all of your students have grades for the assignment. Once you enter assignment grades, your gradebook should start calculating final grades for your students.

The “Scoresheet” tab has some nifty views for analyzing all of the data you are collecting. If you click the “Final Grades” button, you can see how your class is doing on each of your learning targets. If you click the “Student View” button, you can track the progress of individual students on their learning targets.

reassessmentFor reassessments, I make an assignment called “Unit X Reassessment 1” and tie all the targets in that unit to the assignment. As students reassess individual targets, I add the grades to this assignment. If a student reassesses a target from a unit more than once, I make a new assignment called “Unit X Reassessment 2” and record scores there. That makes it easy for me to see how many times a particular student has reassessed a single target.

STEP 6: Tell your students

Lastly, let your students know they can now see their standards-based grades in PowerSchool. You may need your PowerSchool provider to turn on the “standards tab” so students and parents can see scores for their learning targets when accessing PowerSchool from a browser. The app has a “standards tab” built in.

Good luck! Please comment with any questions or clarifications.

Chemistry, more like cheMYSTERY to me! – Heat and Temperature

I fell a little bit behind in posting after I finished Unit 2 in class so now it’s time to play a little bit of catch-up!

Here is a quick recap of where we left off in our model so far…

  • Particles are always in motion
  • Temperature is a measure of the average speed of the particles
  • Pressure is a measure of the number of particles colliding with a surface
  • Pressure and volume are inversely proportional (Boyle’s Law)
  • Pressure and temperature in Kelvin are directly proportional (Gay-Lussac’s Law)
  • Pressure and number of particles are directly proportional (Avogadro’s Law)
  • Volume and Temperature in Kelvin are directly proportional (Charle’s Law)

Unit 2 set up the idea of energy that Unit 3 builds off of. Let talk about energy!

Ice Melting Blocks

I kick off Unit 3 with one of my favorite discrepant events, the ice melting blocks. You can purchase these two black blocks from Flinn. I have students pass the blocks around the room and make some observations. Students observe that one block feels heavier and colder. They infer that the blocks are made of two different materials. I then ask the question, “which block will melt an ice cube faster?” Almost every student will say, “the warm one.” I always get a few students who say, “the cold one because the opposite of what I think will happen always happens in this class!” I put a cube of ice on each block and you can guess what happens:

That is indeed the “cold” block on the right. After students get over their amazement, I have them whiteboard an explanation. This leads to a great conversation about energy transfer and whether “coldness” is transferred or “hotness” is transferred. We also talk about thermal conductivity, refrigerators and some other material science applications.

That demonstration sets us up for the Icy-Hot Lab

Icy Hot Lab

The Icy-Hot Lab (from the Modeling materials) is an incredibly simple lab but still absolutely worth doing. Every year, my students have the same 2 misconceptions coming into this unit: the temperature changes during a phase change and the bubbles in boiling water are made of air. The Icy-Hot lab allows me to address both of those misconceptions

The set-up is easy; students heat a beaker of ice until it all melts and then eventually boils. All the while they are measuring the temperature at a set interval (Vernier Lab Pros are great for this). I used Bunsen burners for the first time this year and got much better results than when I used hot plates in the past.

This lab produces a nice heating curve which gives way to a discussion about thermal energy and phase energy. Students must answer the question, “if temperature is not changing during the phase change, then what is?” When students get stuck here, I ask them to draw particle diagrams for a liquid and a gas at the same temperature. That makes it easy for students to see the difference is in the spacing of the particles. The energy is going into to separating the particles! Now, can they do it backwards?

Cooling Curve of Lauric Acid

I tried a new follow-up experiment this year, cooling lauric acid. Lauric acid has a melting point of about 110 °C so I kept a class set of test-tubes in a warm water bath all day and reused them every period.

During this lab, I uncovered a misconception I didn’t even know my students had. When the lauric acid began to solidify, I heard many students exclaim, “it’s freezing, but the test tube is still warm!”  They could not understand that the word “freezing” doesn’t necessarily mean cold. This lead to a great discussion about what “freezing” means and got us to definitions for the terms “endothermic” and “exothermic.” I also introduced energy bar charts (LOL charts as I like to call them) while whiteboarding this lab.

LOL Charts 

Energy bar charts are an awesome way to get students qualitatively representing energy transfers. I have students complete and whiteboard the energy bar chart worksheets from the Modeling materials.

For the second worksheet, I have students play the “Make a Mistake Game” from Kelly O’Shea. During this whiteboarding session, each group must purposefully make at least one intentional (and as many unintentional) mistakes as they want. It is then up to the class to find the mistakes and ask questions to correct them. As each group comes up to present, I assign a group still sitting as the main questioning group. Other people in the class can pipe in but I want to hear from as many students as possible.

Now that students have a qualitative representation of energy transfer, it is time to put a number on it.

Specific Heat of Copper Lab

I introduced specific heat this year using the balloon and flame demonstration. If you hold a flame under a balloon, it will immediately pop. If you fill a balloon with a little bit of water and do the same thing, the balloon remains intact. I asked my students to explain this phenomenon and they were able to conclude that water must have some special property that allows it to absorb more heat than air. I then ask students what else might affect the quantity of heat transferred into a system. After some probing, students come up with changes in temperature and mass which gives me the chance to introduce Q=mcΔT.

Then, students complete a pretty traditional specific heat of copper calorimetry lab. I am not in love with this lab and I think I am going to take it in another direction next year, just not sure where.

The data from this lab are usually pretty good so it does allow for us to discuss what this number with the crazy units means. I’m just not convinced that the students understand the math they are doing well enough to make it worthwhile.

Calorimetry Calculations

Now that student have been introduced to Q=mcΔT, they can use it to quantify heat transfer. I have students complete the worksheet from the Modeling materials which off simple asking for Q and then gets trickier when students have to solve for things like final temperature. Once students have temperature changes under their belts, we can get into phase changes.

Heat of Fusion Lab

I introduce the concept of “heat of fusion” with another traditional lab, but this one I like a lot. In this lab, students are challenged to determine how much energy it takes to melt ice by assuming that all the energy that goes into melting the ice comes from the warm water they are stirring it into. Students add ice to a styrofoam cup of warm water until no more ice can be melted. They then measure the change in temperature of the water and the volume of ice melted. Using those 2 numbers, students can calculate the quantity of heat that went into the ice and then use the mass of ice melted to figure out the heat of fusion. Again, students get pretty good data from this lab.

Heat of Fusion/Vaporization Calculations

I use the worksheet from the Modeling materials for heat of fusion/vaporization calculations and it is pretty short. To make whiteboarding more interesting, I came up with a new technique I dubbed the “gallery lot.” It is a hybrid between a gallery walk and a parking lot. Each group creates a whiteboard for a problem and props it up around the room. The rest of the class must tour the room and leave post-it notes on boards they have questions about. We then look at each board and give each group a chance to answer the questions posed to them.


Combined Calorimetry Calculations

Once students have mastered calculating energy transferred during a temperature change and phase change individually, it is time to combine them! I approach this hurdle by having students break down the process for a simple situation: ice at -10°C is melted, heated to boiling and boiled away. First, students construct the heating curve. Then they figure out which equation they need to use for each region of the curve. Finally, they plug in the measurements and add up all the Qs.


Students then complete the worksheet from the Modeling materials that goes with this topic and we whiteboard it the next day. I would like to say that these calculations are a breeze after that, but that would be a lie. I tell my students this is the top of Unit 3 mountain and they will get a little bit of a brain break in Unit 4. To get to the very top of the mountain, I give my students a Lord of the Rings inspired challenge problem where they must calculate the amount of energy needed to melt the gold statue in Desolation of Smaug.

With all of that covered, there is only one thing left…

Unit 3 Practicum

The main reason I keep the traditional specific heat lab I mentioned earlier around is for the practicum I am currently using. Using the same lab procedure from the specific heat lab, I challenge students to use copper shot heated to 100°C to raise the temperature of room temperature water to 25.0°C. Students need to rearrange their equation from the lab to solve for mass of copper.

I like the challenge of this practicum but I think it is too narrowly focused. Next year I think I will give students an energy transfer to measure and they will have to construct the LOL chart and temperature-time graph for the scenario and calculate the quantity of heat transferred.

Unit 3 is hefty! Let’s sum it all up with the model so far…

  • If temperature is a measure of the “hotness” of a system then heat is the quantity of “hotness”
  • Heat can go into a system (endothermic) or flow out of a system (exothermic)
  • Heat can be stored in 2 energy accounts: thermal and phase
  • A change in thermal energy means a change in particle speed and is shown by a slope on a temperature-time graph
  • A change in phase energy means a change in particle spacing and is shown by a plateau on a temperature-time graph
  • The quantity of heat transferred during a temperature change can be calculated using the mass, specific heat and change in temperature for the system
  • The quantity of heat transferred during a phase change can be calculated using the mass and heat of fusion or vaporization for the system

Don’t worry, we will cool it down a bit in Unit 4 (see what I did there :0).


Chemistry, more like cheMYSTERY to me! – Particles in Motion

Here is a quick recap of the model so far from the previous post in this model building series:

  • All matter is made of tiny,  indestructible, hard sphere particles
  • The number and size of the particles determines the mass of the substance
  • The number of particles in a closed system does not change
  • The number of particles in a certain amount of space determines the density of the substance
  • Particles are really small; on the the order of 10^-9 m or 1 nanometer.

Unit 1 was all about building a functional model of a particle. Unit 2 is the first time students will make an observation that doesn’t fit their model, and they will have to amend the model. Let’s jump right in!

Diffusion Demonstrations

I start Unit 2 with the diffusion demonstrations outlined the Modeling Instruction materials. First, I place something with a strong scent on a watchglass, and place that on a triple beam balance. I have used different extracts, fresh-squeezed orange juice and essential oils for this. They have all worked about equally well for me. I ask students to raise their hands when they smell the scent. Students observe that the smell travels around the room randomly. I then ask students to whiteboard what they think is happening. They come up with many different explanations but the conclusion we come to is that the particles must be moving! We have added something to our model!

We refine this addition to the model by observing what happens when you drop food coloring in warm and hot water.

From this observation, students infer that particles move faster in hot water and slower in cold water. Therefore, temperature is a measure of the average speed (kinetic energy) of the particles.

To end this demo day, I show students a thermal expansion demonstration.

Students observe two liquids (water and isopropyl alcohol) rise up capillary tubes as they are submerged in a hot water bath. The yellow liquid (alcohol), appears to rise more quickly than the red liquid (water). Students immediately respond that materials expand when they are heated but it takes a little more probing to get them to explain what is happening at the particle level.  This allows us to talk about how a thermometer works. I also talk about Celsius and Fahrenheit here and where those scales come from.

Now that we know that particles move, we can ask some interesting questions, like, “how does a straw work?”

“How Does a Straw Work?” Discussion

For this discussion, I tell all my students to bring a drink to class with them.  I then give every student 2 straws. The first questions is simple, take a drink with your straw and tell me how it works.

I get all sorts of answers to this question and hear lots of sciencey words like “pressure, vacuum” and my favorite “sucks.” It always becomes very clear that students actually have no idea how a straw works. The first step is to get them to see that nothing is being “pulled.” That means, the liquid is being pushed up the straw. But by what? Enter pressure. I also have students try to drink out of their straws with one on the inside of their drink and one on the outside. This helps cement the idea that you remove particles from your mouth to create a partial vacuum when you use a straw. Then the air on the outside of your drink is able to push your drink up the draw. I end class that day by asking the question, “is there a maximum straw length?” and showing the Veritasium video, “World’s Longest Vertical Straw.”

Now that we have defined pressure, we can figure out what affects it.

Gas Laws

I have moved to completely separating each gas law and then combining them in the end as opposed to deriving all the gas laws during one lab. I start the discussion by blowing up a balloon and asking, “what could I do to change the pressure in this balloon?” Students are able to come up with, “change the volume, change the number of particles, and change the temperature.” From there we explore each of the gas laws, starting with Boyle’s Law.

To explore Boyle’s Law, students use Vernier Lab Pros connected to TI-83 plus calculators to graph the relationship between pressure and volume.  Students push in and pull out the plunger on a syringe connected to a gas pressure sensor to collect 8 data points.

Students whiteboard their data and we are able to determine that pressure and volume are inversely proportional by the shape of the graph. I no longer have students linearize this graph because I do not think it adds enough to the discussion to be worth the time it takes to teach them how to linearize.

For each gas law, I have students draw 3 particle models to show what is changing and how that change affects the pressure. After discussing the relationship between pressure and volume, students work on just pressure-volume problems with initial-final-effect tables.

For Gay-Lussac’s Law, students again derive the relationship by collecting data with Vernier LabPros. This is an interesting whiteboard meeting because students collect their temperature data in Celsius and so their y-intercepts are far from zero.  I ask students, “what would a y-intercept of zero mean?” Students are able to reply that it would mean the particles are no longer moving which would be absolute zero. Usually one student in the class remembers something about Kelvin at this point and what temperature absolute zero is. We then have a quick discussion about why scientists use Kelvin and the need for a temperature scale without negatives. With all of this in mind, students then work on just pressure-temperature problems.

I cut the Avogadro’s Law lab this year to avoid confusion with terms like “puffs” because students do not know how to count particles yet. Instead we talked about Avogadro’s Law and Charle’s Law and how they make sense at the particle level. Avogadro’s Law will come back at the end of the year when we get into PV=nRT.

This year, I added a day of gas laws review day before jumping into combined gas law problems. For the review, students whiteboarded a graph with particle models and a statement of relationship for each gas law. Students also put this information on a summary sheet for themselves. From there, we were able to cleanly transition into combined gas law problems with initial-final-effect tables.


That is the last major topic in Unit 2! All that’s left is a challenge problem and a practicum!

Challenge Problem

To wrap up the gas laws, I give students a challenging ranking task that a colleague of mine created. It challenges students to use their conceptual understanding of the gas laws instead of relying on their math skills. The ranking task gives students various scenarios like, “the volume is doubled and the temperature is halved”, and “the volume is tripled and the temperature is tripled.” The students must determine what effect the scenarios would have on the pressure and rank them from least to greatest final pressure. 


For my Unit 2 practicum,  I use the term “practicum” loosely. For the practicum, students are not challenged to solve a problem using their model but rather explain various demonstrations using their model.

I have students explain a lung model,

a marshmallow expanding in a syringe,

an water balloon being pushed into the mouth of a flask,

and the always fantastic “Crush the Can” demo using the gas laws. The students always find these demonstrations are not as simple to explain at the particle level as they first appear.

To sum up what we added to our model so far…

  • Particles are always in motion
  • Temperature is a measure of the average speed of the particles
  • Pressure is a measure of the number of particles colliding with a surface
  • Pressure and volume are inversely proportional (Boyle’s Law)
  • Pressure and temperature in Kelvin are directly proportional (Gay-Lussac’s Law)
  • Pressure and number of particles are directly proportional (Avogadro’s Law)
  • Volume and Temperature in Kelvin are directly proportional (Charle’s Law)

Whew! That is a hefty unit! Look out for some more additions to the model concerning energy in the next post of this series!