Using Student Videos as Test Corrections/Reassessments

Each year, I seem to dabble around with 3-4 different methods of implementing some form of a retake policy.  Though I desperately want to just fully commit to one policy, the lack of my own satisfaction after the policy had been implemented continued to hang around.  Usually, the frustration with coming up with an effective policy would revolve around a few consistent factors:

1. The amount of work that I had to put in to make the policy successful was significantly greater than the amount of work that my students had to put in to achieve points back on their original assessment score.
2. The evidence that would be expected for the students to provide in order to demonstrate that they had learned from their mistakes was hard to identify.  Some students would do a great job at writing out what exactly they did wrong and why their new answer is correct while others either lacked the reasoning/communication skills to provide evidence of learning or they would simply get lazy with their evidence and focus primarily on the right answer.
3. The whole logistics of it.  Is it OK to let students take the test home and correct their answers?  If there is going to be an actual reassessment, does it have to be done on a certain day?  Should students correct their test with me physically present in the room?  Do you give full points back?  What if a student's explanation/answer is still incorrect on the test correction?  Can anyone come in at any time to do their corrections?  Once corrections are made, is that sufficient evidence for me to bump up their grade?  There are many others questions that I had (and still have) that have made the logistics of a test correction/test retake a logistics nightmare.

OK, so to summarize.....

1. Too much work for me
2. What evidence would convince me that learning has occurred? 
3. Logistics nightmare

After taking some time to think about these things, I started to focus more on the evidence portion of my concern and try to figure out my other concerns once I knew exactly what I expected from my students.  What would really convince me that a student has learned from his original mistake?  Well, he would need to be presented with a new situation that would require the same reasoning and conceptual skills as the original situation.  He would also need to explain his reasoning throughout the problem so that I know there is no masking of true understanding (i.e. memorizing a process or an answer).  Lastly, he would obviously need to have the correct answer.

Ideally, I wish I could have a 1-on-1 sit down with each student who is interested in learning from their original mistakes.  I would give them an opportunity to go to the whiteboard and draw or explain to me whatever they needed.  I could hear them think out loud as they were solving problems on the board.  However, I have 170 students and this is not an ideal world.  Such a task would bring me back to my logistical nightmare.  

So if it's really the explanatory evidence that will convince me that learning has occurred, how can I provide my students with an opportunity to demonstrate such evidence?  This is where the app Explain Everything came in.  Explain Everything is essentially a screencasting tool that allows the user to record everything they draw and say.  It allows the easy import of pictures, videos, pdfs and it has a million features that make the app really intuitive and highly effective for creating tutorials.  I've even taken advantage of this app for the past year to make all of my tutorials for my classes.  

The general idea was simple: students will create videos (screencasts) that will demonstrate their new understanding of specific learning objectives.

Because the questions on my tests were tied to specific learning objectives, students would first have to identify which learning objectives they had the most trouble with and identify how many points they lost for each learning objective.  In order to make this process easier, I created this reassessment form.  Once completed, the student would have to submit this form into our LMS Schoology so that I could easily refer to it at any time.

For each learning objective, I created a new set of questions that were identical in number.  In other words, if there were 5 questions on the test tied to objective 12-3, then I created 5 new questions that required similar reasoning skills to demonstrate understanding of that objective.  Once the questions were created, I placed them into a pdf.  Because I had 6 learning objectives on this test, I made 6 pdfs.  All pdfs were uploaded to Schoology so that the students could easily access them.

From there, students would need to import each pdf (learning objective) that they were interested in reassessing into their Explain Everything screencast and record themselves solving each problem.  

Because the majority of my students had never been placed in a situation where they needed to make a screencast, I could tell it made many of them a bit uncomfortable--which is understandable.  However, one thing I can definitely attest to is the fact that watching and listening to their videos gave me an insight into their thought process that wouldn't have been possible before.  Not only was I able to identify mistakes in writing but, most importantly, I was able to easily listen for misconceptions in reasoning.  On the other hand, I was also able to to easily listen for great examples of perfect reasoning.  While some of the student videos were rather dull and straight to the point, several videos made use of their creativity and it was clear that significant time was spent in thinking how to achieve the idea of "how do I explain this problem to my teacher"?  I've included a couple sample videos below:

Sample Vid #1

Sample Vid #2

Sample Vid #3

The above videos aren't without mistakes within them.  But the whole idea is that it was VERY clear to me what a student knew and what a student doesn't seem to quite understand.  Sometimes it's easy to identify misconceptions simply based on work.  But sometimes it's not.  Allowing myself to actually hear them explain their thought process allows this ambiguity to go away and for evidence of learning (or lack of it) to be clear.  

After creating the video, students were required to submit it to Schoology like they would a regular assignment.  The satisfied the logistics problem since all videos were in one spot and I could watch them whenever I wanted.  

As far as the work for me, all I had to do was watch and take simple notes on their reassessment form that was submitted.  Based on the time length of their video, this process was simple.  Next time I'll put a cap on how long a video can be.  A couple samples of what I did while simultaneously watching the video are below:

Though there are still things that I want to tweak about this process, it really was the first time that I was satisfied with the evidence provided of student learning.  I think student videos could be a great tool for assessments in the future and I'm going to continue to find ways to incorporate them into my classroom.

Inquiry-Based Analogy Experiment to Rutherford's Discovery of the Nucleus

As I mentioned in a previous post on the electron, I believe atomic structure is taught WAY too early in a typical chemistry curriculum.  Having looked through a few chemistry textbooks laying around my house, I continuously found that atomic structure (and atomic theory as a whole) is introduced as early as Chapter 2 and as "late" as Chapter 5.  Considering the hundreds of years worth of scientific achievement and failure that took place before the discovery of subatomic particles, why do so many teachers present the inner workings of the atom so early?  Having knowledge of such information is simply not needed in order to explain some of the most important early concepts in chemistry such as:
1.) conservation of mass
2.) the role of energy in phase transitions
3.) particle motion
3.) gas laws
4.) density
5.) the existence of atoms
6.) atomic attraction
7.) Law of Definite Composition and Multiple Proportions
8.) Avogadro's Hypothesis and the mole
9.) % composition and empirical formulas

Though I'm sure there are other important concepts in chemistry that were known before the discovery of subatomic particles, I believe the above list suggests that a great deal of chemistry can be learned before having knowledge of atomic structure.  PLUS....this is how it was historically done!  Before the 1890's, early chemists had no knowledge of subatomic particles.  So in our classrooms, why do so many teachers simply bypass the knowledge accumulated prior to Thomson and present the whole idea of atomic theory so early?  It's simply not needed and it makes things more complicated.

I typically don't introduce the unit of atomic structure until 2nd semester.  By the time we reach this unit, my students' only true knowledge of atomic theory lies on the shoulders of Dalton.  Obviously I know they are aware of words like electron, proton, and neutron, but I don't allow them to use those words in their explanations prior to this unit because they have yet to understand the evidence for such ideas.  Early chemists couldn't use those words either because the words didn't exist yet!  

In order to keep it historically accurate, we approach the discovery of the electron first which I've written a post about here.  Though I deviate from the history accuracy a little bit by including Milkian's oil drop experiment, I only bring it up because we are currently talking about the electron anyways.  After we analyze the evidence for the existence of electrons, students realize that Dalton's model of the atom needs to be replaced and in comes the plum pudding model.  

Up next comes Rutherford.  But before I even mention anything about Rutherford's gold foil experiment, I get the students to perform a simply analogy experiment.  They don't know what it's an analogy for yet, but they will once we start talking about the details of Rutherford's experiment.  The goal of the analogy experiment is this:

Indirectly calculate the diameter of an unknown object by recording the number of times it is hit with objects of a known diameter

A link to the lab activity can be found here

The setup is incredibly simple and the I would imagine nearly every science teacher has access to similar materials that would get the job done.  The general procedure is simple as well.
1.) Students setup a well-defined path with meter sticks parallel to each other.
2.) A whiteboard (or some sort of large opaque material) is positioned at the end of the path on top of the meter sticks so that there is a cm or two of space below.  
3.) The group is given 100 pennies and they are to measure the diameter and therefore determine the radius of the penny.  They also measure the width of their path.
4.) One student is assigned the role of "shooter" or "bombarder" and is given 100 pennies and is also blindfolded.  I've also gone to the extreme and made the "bombarder" wear headphones as well.
5.) The other group member is given an object and is told to place that object on the other side of the whiteboard.  The "bombarder" does not know where the object is and knows nothing about its size or mass.
6.) Once the non-blindfolded group member has measured the diameter of the "unknown" object, that group member places the object wherever he wants behind the whiteboard.
7.) The "bombarder" now shoots the pennies one by one, typically in groups of 10, and the other group member counts how many times the object is hit.  Because the "bombarder" cannot see, it is important that the other group member makes sure the path is cleared of pennies in order to ensure that each penny has a fair chance at hitting the object.
8.) Once all 100 pennies have been shot, the total number of hits is recorded and the analysis ensues.

The entire setup looks like this:

Using the information recorded and a simple equation, students are able to arrive at an experimentally-determined diameter of the unknown object.  I have had great success with this and I often see groups get within 1 or 2 cm of the actual diameter.  In order to ensure success, it's really important that the "bombarder" is truly shooting at random.  If the "bombarder" knows where the object is, it's almost impossible to convince a teenager to NOT try to purposely hit the object.

So why the heck did we just do this?

Well, without going into much detail, not only did Rutherford's experiment lead to the discovery of the nucleus, but it also led to the indirect determination of the size (diameter) of the nucleus relative to the rest of the atom.  In my experience, students have no issue with the conclusion of alpha particle scattering being the result of hitting the nucleus.  However, using that scattering information to determine the size of the nucleus is a much more conceptual idea and much tougher to grasp.  By doing this analogy activity, students see that it is actually possible to determine the diameter of something without actually being able to see it.  I think that's pretty cool!

After the activity is over and they've calculated and compared their experimental diameter to the actual diameter, class is pretty much over.  When they go home, I tell them to watch this video where I describe some of the fundamental points about what we just did in relation to Rutherford's experiment--which we talk about the next day.

If you haven't already figured it out by now, here are the most fundamental points to the analogy activity:

• penny is analogous to alpha particle
• unknown object is analogous to nucleus
• path width is analogous to diameter of atom
• penny bouncing back a various angles is analogous to extreme alpha particle deflection when hitting the nucleus
• vast majority of pennies going straight through suggests unknown object is small relative to path width which is analogous to vast majority of alpha particles go straight through gold fold with little to no deflection due to the nucleus being so small relative to the size of the atom
• empty space directly behind whiteboard is analogous to the majority of the atom being empty space
• penny bouncing back suggests unknown object is much more massive than penny which is analogous to the idea of the nucleus containing nearly all the mass of an atom (and much more massive than an alpha particle--at least gold's nucleus)

I believe having this experience PRIOR to discussing Rutherford's experiment lays a strong foundation for our students to more easily connect the rather conceptual findings from Rutherford's experiment with what we did the previous day.  

By no means do I think this is the BEST way to do things but I do know that it's better than simply approaching the inner workings of Rutherford's experiment head on and assuming everyone will just "get it".  When teaching such abstract concepts in chemistry, the more connections we can give our students to make with prior experience, the more easily they will be able to assimilate such experiences with the appropriate concept.  

Modeling Ionization Energy with "Modeling Chemistry"

Simply Google ionization energy and you will quickly find a vast amount of images that appear like this--or at least similar to this:

To you and me, this image makes sense.  It makes sense in the context that it tells me so much about some of the properties of many of the elements.  But how do we get our students to interpret the numerous peaks and valleys within this image?  Better yet, how do we get our students to understand the reason for such peaks and valleys so that such an interpretation is valid?

For the sake of simplicity, ionization energy is the energy required to remove an electron from an atom.  I have no problem defining it this way in high school chemistry and I also have no problem simply giving students this definition.  I may even go into slight detail as to how this amount of energy is actually measured, just to make these numbers appear less dogmatic.  However, I do have a problem with giving them this definition and then simply showing them the trend (specifically, the 1st ionization energy trend) right off the bat.

How do we know this is the trend?  Why is this the trend?

I imagine many educators often adopt the use of actual ionization energy data for many elements, have students graph the ionization energies for each electron for a few elements, provide an explanation of the data with the Bohr model, use ideas such as Coulomb's Law to provide further explanation, and then call generally call it good.  To be honest, I don't really have any inherent disgust to this approach or anything.  Heck, it's pretty much what I do!  But I do think it leaves out (or limits) an important facet of science that we continuously try to help our students understand--the use of models to explain phenomena.  We give them the data, we give them the Bohr model explanation, we give them Coulomb's Law to help understand why an electron further away from the nucleus is easier to remove than an electron that is closer.

Where is the natural investigation in this?  Where are the individual ideas that the students have to provide explanation for this trend?  Where is the debate among competing ideas in class?  Where is the class consensus derived from their ideas?

To be clear, none of us honestly expect our students to provide some perfect explanation for such a trend based on their limited knowledge and application of such things like the Bohr model and Coulomb's Law.  So what do we do instead?  In my opinion, we provide a situation for them to create a model that, in general, provides an explanation for the data.  Such models are created in small groups, presented to the class, accepted or rejected based on their explanatory power, and then we come to a consensus on the best model.  All of this can be done without thinking of it in terms of atoms or the Bohr model--which itself has many faults in its explanatory power when it comes to ionization energy.

So here is how my chemistry classes approached the idea of ionization energy (not just 1st ionization energy) this year.

First, students were actually given the ionization energy data for each electron within the first 20 elements.  Students were then asked to graph the ionization energy (IE vs. # of electron) for each electron for Be, Si, and Ca.  This produces the following graphs:

What do we make of this?  Keep in mind that students have no idea of the "too-often-taught" 2-8-8 idea.  I have my own issues with that but I'll leave that alone for now.  We just picked 3 elements, graphed their ionization energies--do we notice any patterns?

1.) It appears that there are always 2 electrons that are REALLY hard to remove.  They are clearly in their own "group" and this appears in all 3 graphs.

2.) When supplied with enough electrons (as in Si & Ca) there seems to be a 2nd group that seems to consist of 8 electrons.  

3.) If we "zoom in" on the Ca graph by changing the y-axis max value, we notice that there is another group of 8 and then what appears to be another group of 2.  I must mention that this is where many students may often get the misconception that the 3rd energy level can only hold 8 electrons.  I tell them that, based on our evidence in front of us, this is so.  Later, when we investigate electron orbitals & configuration, that misconception gets resolved quickly.

At this point, the feature of the Bohr model that we are going to focus on and assimilate into our own model is the idea of different energy levels and the association energy required to remove an electron at such energy levels.  The model that we start to develop comes directly from the Modeling Instruction material and it is commonly known as the "men-in-the-well" model.  The reasoning behind it is rather simple and it goes a little something like this.

An energy well is drawn and a small stick figure is placed at the bottom like the image below.

energy well model of hydrogen atom

Person = electron

Getting the person out of the well is a metaphor for removing an electron from an atom, which requires energy.  The amount of energy required to pull out the person from the well depends on where the person is in the well and how deep the well actually is.  I'll go over a few examples and some of the original ideas that my students had but I think it's important to remember that the men-in-the-well idea is easy to visualize relative to the Bohr model.  Kids have past experience with pulling a friend or getting on someone's back to reach a higher spot.  They can actually imagine pulling someone out of a well and can easily distinguish which person would be easier to remove.  No experience in their lives can relate to what actually takes place at the quantum level within the Bohr model.  Therefore, we create this model to supplement what takes place at the atomic level.

So I show students what the model would look like for H and He.  It's incredibly important to stress to the students that the model must accurately reflect the data.  In other words, if one electron is easier to remove than another, my model must be able to explain that both visually (from the picture) and verbally (from the people who drew it).  So, below are the IE data for H and He.  All ionization energies are in electron-volts.

                                                                                            H             He

                                                                              1st       13.6         24.6  

                                                                              2nd       ---           54.4

After looking at this data, a couple things need to be explained.  

1.) Why is the 1st electron of hydrogen easier to remove than the 1st electron of helium?

2.) Why is the 2nd electron in helium more than 2x as hard to remove than its 1st electron?

Remember that even though we are using atomic data, we are NOT using atomic vocabulary in our models or explanations.  We're talking about people instead of electrons, depth of well instead of distance from nucleus, people helping each other get out instead of electron repulsion, etc.  So, I post this H and He data on the board and have the hydrogen "energy well model" shown.  

Instead of just telling them what I should do, I ask the students "how could I draw the well for the helium considering the fact that the 1st person in the helium well is harder to remove than the person in the hydrogen well?"

Honestly, it only takes a few seconds before several students simply say something like "make the well deeper".  Ok, so I make the well deeper and I get a comparison that looks something like this.

So we go back and try to see if this model accurately answers the first question:  Why is the 1st person in hydrogen easier to remove than the 1st person in helium?  The students easily agree that it's simply due to the fact that the helium well is deeper.  Makes sense.....but what about the 2nd question: Why is the 2nd person in helium so much harder to remove the 1st person in helium?  This is the beginning of when it starts to get creative and interesting with regard to their explanations.  Possible explanations have been

1.) Maybe the 1st person can jump higher to catch the rope hanging down

2.) Maybe the 1st person is taller

3.) Maybe the 1st person is stronger

4.) Maybe the 1st person is thrown upward by the 2nd person

5.) Maybe the 1st person gets on the back of the 2nd person to get up higher

6.) Maybe the 1st person stands on the shoulders of the 2nd person to get up higher.

After hearing a few potential explanations, I make one thing clear:

1.) All people (electrons) are the same in height, weight, strength, desire to want to leave, etc.

Having said this, it immediately gets rid of explanations like 1-3.  However, explanations 4-6 all have an important similar quality to them that should be recognized--they each involve the 1 person helping the other.  We start to focus on this idea for a bit and because it's easiest to draw, we settle on the explanation of the 1st person getting on the shoulder of the 2nd person in order to get higher up.  So even though the helium well is deeper, our model still makes sense if we assume the 2nd person in the helium well somehow helps the 1st person in the same well get out.  This explains why the 1st person is easier to remove from the well since the 2nd person has no one to help him.  We settle on this general approach and everyone seems to be satisfied with the explanation and the model.  

At the point, I should address to you that the students, by themselves, just naturally came up with the concept of electron repulsion.  I realize that they didn't use the words electron repulsion but coming up with this concept of 1 person helping the other to explain the data lays a solid foundation for when we start to include a concept like electron repulsion.  It won't be hard for students to just be like, "oh, that's like when the people were helping each other out of the well."  Building these models helps our students assimilate certain concepts that they constructed within their own mind into somewhat difficult concepts more easily, like electron repulsion.

Ok, so now we have accurate models that we all agree on that represent H and He.  But what about the other elements?  What about lithium and beryllium?  At this point, I split the class into several groups of about 2-3 students each.  On their whiteboards, they are to present the following things:

1.) IE data for Li and Be

2.) Energy well model for Li and Be

3.) Either a brief written explanation on your board OR just rely on your own verbal skills to provide an explanation orally.  

I'll give you 10-12 mins.....GO!

Here is the IE data for Li and Be:

                                                                                          Li             Be

                                                                1st                     5.4            9.3

                                                                2nd                   75.6          18.2

                                                                3rd                    122           154

                                                                4th                     ----           218

A couple things to address:

1.) 1st person in Li easier to remove than 1st person in Be

2.) Why the HUGE drop between 1st and 2nd people in Li and the HUGE drop between 2nd and 3rd people in Be?

3.) Why is the 2nd person in Be easier to remove than the 2nd person in Li?

Here are a couple whiteboards representing slightly different and creative ideas:

As a teacher, the most fascinating part about letting the students come up with their own explanations is what occurred in the bottom whiteboard.  Within that group, they could not come to an agreement.  Two girls had one idea while the other 2 girls had a different idea.  In other words, they had two competing theories.  I told them to put both on the board and let the class decide which theory has better explanatory power.  THIS IS HOW SCIENCE IS DONE!!!!!

Anyways.....take another look at the boards and see what students came up with on their own--the idea of energy levels!!!  At no point in time did I tell them they needed to add a step or some sort of board sticking out the side of the well.  Using their own reasoning and bit of creativity, they came up with this idea that within the well are boards that the people can stand on that allow them to be higher up and therefore easier to remove.  Pretty cool!  Now that they have this concept created, it will be way to easier to understand the idea of electrons occupying energy levels further away from the nucleus are easier to remove than ones closer.  

Though I could type out the merits and faults of each model presented, it would take too long and chances are, you can see some of them for yourself.  However, I will say we had a really good debate in class about which models more accurately represented the data.  In the end, we naturally arrived at a series of models that looked something like this:

We believed these models were sufficient because they were able to explain the original questions we posed:

1.) The 1st person in Li is easier to remove than the 1st person in Be because the 1st person in Li is up higher.

2.) The HUGE gap between the 1st and 2nd persons in Li can be explained by the fact that the 1st person is up on some sort of shelf or board sticking out of the side of the well which allows him to be much higher up than the 2nd and 3rd persons.  Same thing goes for the 1st and 2nd persons in Be compared the the 3rd and 4th persons in the same well.

3.) The 2nd person in Be is easier to remove than the 2nd person in Li because he is higher up.

In addition.....

4.) The 1st person in Be is easier to remove than the 2nd person in Be because the 2nd person helps the 1st person escape.  Same thing goes for the 3rd person compared to the 4th person.

5.) Remember those 2 electrons that kept showing up isolated in the top right corner of the graphs earlier?  Our energy well model accounts for those 2 electrons by consistently putting them at the bottom of the well since they're the hardest to remove.  This sets the stage for the number of electrons that can occupy an energy level.  If you were to keep going with these energy well models, you find that a max of 8 people should fit on the next shelf in the well.  Again, the model is naturally building the foundation for scientific concepts that we will be talking about later (like electron configuration, bohr model, and even how electrons move from different energy levels.

We continue to draw models and provide explanations for every bit of detail for most of the 1st 20 elements.  Like most models, these energy well models have faults.  For example, it doesn't take into account the different type of orbitals that exist within certain energy levels.  When certain anomalies come up where we can't quite use our models to explain the data, I simply tell them that they will get resolved later.  They do  eventually get resolved once we get into electron configuration.

What was cool about introducing ionization energy patterns this way was the inclusion that was given to the students.  I introduced a model that we could work with and they just sort of ran with it and edited it in order to better explain the data.  Some worked out while others didn't.  We had conversations about why one model was better than the other and we eventually came to a consensus on the most accurate of models.  This is the process we want our students to experience when we introduce different scientific concepts mainly because this is how science is actually done.  I have no doubt that many of the students would've been just fine if I had just explained to them the ideas of electron repulsion, energy levels, and Coulomb's law but the whole process of discovery, failure, and discourse would've been substituted with a much more dogmatic approach.  The more we can include our students in the investigation and the process of understanding how certain concepts can be understood, the more fun we can have in the class and the deeper the overall understanding can be.

Approaching the electron in "Modeling Chemistry"

The vast majority of chemistry textbooks that I have dealt with both in high school and college approach the atomic structure quite early in the book.  In my opinion, far too early.

The picture above shows the table of contents from the chemistry textbook that is currently in my high school classroom.  This book had been purchased by the school in '03 so it had already been in my current classroom for nearly 10 years before I arrived.  

So what's wrong with this picture with regard to the atomic structure?

The problem that I, and probably most modelers, have with the positioning of where learning about atomic structure is expected is far too early.  If you take a moment to essentially exclude the typical chapters on "Into to Chem" and "Scientific Measurement", the atomic structure is basically the 2nd unit in the curriculum!  What frustrates me so much about this approach is that the entire inner-workings of the atom are all of a sudden thrown right at the students and it encourages them to accept all we know about such inner-workings before any evidence has been brought to their attention that atoms exist in the first place!  I mean, let's be real, the idea of "atomic structure" didn't become a big topic of discussion within the scientific community until the very late 1800s.  Is there nothing that students need to learn prior to J.J. Thomson's famous cathode ray experiment besides classifying the different between a physical and chemical change?  

Since this post is related to the electron, surely the current textbook will compensate for having such a chapter so misplaced by provided a mountain of evidence for the electron's existence and its properties right?  You tell me....

The discovery, charge, and the mass of the electron are given an entire 3/4 OF A PAGE!!  Are you kidding me?  Now, it's entirely possible that many teachers who use books such as this have access to cathode ray tubes, or do experiments that are analogous to what Thomson and Millikan did but how many of them simply rely on the following notion:

 "we know of the electron's existence, here are some of it's properties that we know of, now let's move on to protons"

Not only do Thomson and Millikan deserve more respect but, most importantly, our students deserve a greater depth into the scientific reasoning and evidence that led to such a fundamental discovery.

Though this entire topic of proper placement of units could easily fuel a writing binge for several hours, I digress.  After all, I'm here to talk about how I approach the electron.  

It is now 1/2 way through our THIRD quarter and, as of one week ago, we just started to begin our unit on Atomic Structure: The Inner Workings of the Atom.  After finishing up our Counting Particles unit where the concept of the mole model was introduced, I felt that moving on to atomic structure was appropriate.  Because it has not been completely decided in my mind how I will be approaching the proton, neutron, electronic configuration, radiation, and isotopes, I will only focus this post on how I approach the electron in my classroom.  I will bring up those other ideas in another post I'm sure.

Sticky Tape Lab/Activity:

This is an awesome paradigm lab that was first shown to me using the Modeling Chemistry curriculum.  Students place two pieces of tape on top of one another with the bottom piece sticky-side down on a base piece of tape and the top piece sticky-side down on the bottom (middle) piece of tape.  Then they peel the top two pieces of tape off slowly from the base tape, ground the bottom tape with their fingers so that both pieces of tape are essentially neutral (though the students don't yet know why they're doing that part) and hold them up.  Next they quickly rip both pieces of tape from each other and immediately they notice that new properties have arisen in both pieces of tape--they're charged.  To investigate this new property of charge, students place their top tape, bottom tape, strip of Al foil, and strip of paper somewhere in the room so that they are all hanging over a ledge.  Making a new top tape and bottom tape, in the same fashion they made the original ones, and cutting out two new strips of Al foil and paper, they are able to investigate how each strip reacts when any one of the new four strips are placed near them.  Students organize their observation in a table like the one below:

 After the data has been collected, a nice discussion follows between myself and the class that is structured in the following following presentation which was mostly taken from a presentation within the modeling chemistry folder for this unit.

Sticky Tape Lab Discussion

The most important part of the discussion is what we are able to eventually conclude.  Whatever is responsible for changing the properties of our tapes is:

1.) Smaller than an atom

2.) It's mobile

3.) It has a charge

Just based on those conclusions alone, we are able to deduce that our current model of the atom, which is essentially a billiard-ball-like structure needs to be changed--something is inside it!

Thomson's Cathode Ray Experiment:

In the past, I've focused heavily on this experiment mainly via lecture due to our current inability to replicate the experiment (no cathode ray rube).  The pure beauty of this experiment had always driven my passion to talk about it.  It wasn't until around my 3rd year that I realized I was making the learning involved about this experiment more about myself than my students.....I LOVED talking about it!  Because of this, I've toned it back quite a bit and have instead used a variety of videos on youtube where others are replicating the experiment with an actual cathode ray tube.  Students use their iPads to watch a variety of videos that correlate to specific questions.  In addition, I give them the opportunity to read through small excerpts of Thomson's Nobel speech from 1906.  The main goal of this part in the development of the electron in our model of the atom is to understand how we know the electron has a NEGATIVE charge.  Thomson's experiment confirms what we had already known from the sticky tape lab.  That is, we knew it was mobile and smaller than an atom.  Now we know its charge is negative.  It is at this point in time we develop the "plum-pudding" model since we now know the electrons have a negative charge.  Also, we go back to discussing why the Al foil and Paper were attracted to both the top and bottom tape even though the foil and paper were neutral.  The PHET simulation below that involves a balloon, a wool sweat, and a wall has served useful for visual purposes.

Balloons & Static Electricity PHET simulation

How Much Charge Does the Electron Have?  Millikan's Oil-Drop Experiment:

Though I would LOVE to replicate the actual experiment, it's simply not possible with current resources.  Instead, what I do is split this idea of the magnitude of the electron's charge into 2 steps:

1.) Watch an 11-min video made by me that has questions sprinkled throughout, using Educanon, on how Millikan performed his oil-drop experiment.  I briefly discuss the apparatus, the purpose, the logic, and an extremely over-simplified version of his data.  The video can be seen below.  You will not be able to see the questions because the students view it using Educanon.  The quality was below what was originally on my iPad and I just didn't know the quality goes down from iPad to youtube but I suppose that's part of my learning experience in relation to making videos.

Millikan's Oil Drop Experiment

2.) After watching the video, many students still have questions about how Millikan was able to determine the charge.  Because of this, we do an activity that serves as a great analogy to the oil-drop experiment.  This activity was taken directly from Flinn Scientific and it produces great results and discussion.

Discovering the Charge of an Electron: Analogy to Millikan's Oil Drop Experiment

The purpose of the analogy activity is to determine the mass of a single BB without weighing any KNOWN quantity of BBs.  Just like Millikan determined the charge of a single electron without knowing how many electrons he was dealing with, students determine the mass of a single BB indirectly and eventually use this calculated individual mass to successfully predict how many BBs were collected using a certain length of magnetic stip in a particular weigh boat.  

The magnetic strips are analogous to the oil droplets and the BBs are analogous to the electrons.  Predicting the number of BBs that are attracted to a certain magnetic strip is analogous to determining the charge of an oil drop.  Determining the smallest difference in mass between two trials of BB collection is analogous to determining the charge of a single electron.  All of this is done without ever knowing, until the very end, how many BBs you are actually dealing with at any given point in time.  My own description of this may be a bit hard to follow so I recommend reading over Flinn's description or my own modified procedure and analysis of this activity below.

Procedure & Data Collection

Calculations & Analysis

At this point in the unit we have determined the following things ALL BASED ON EVIDENCE.

• electrons are smaller than atoms (how much smaller will come later)
• electrons have a negative charge
• the charge of an electron is approximately -1.6 x 10^-19 C (the actual magnitude of the charge was derived based on over-simplified data from me....but it was still derived from data)
• electrons are mobile

As mentioned above in the first bullet point, I plan to do some sort of investigation tomorrow or the day after that is centered on determining the mass of the electron--or at least how Thomson determined the charge to mass ratio and what that indicated about the mass of the electron.  I will edit this post at a later point once I've come up with an activity to do so.

Anyways, if you made it this far into my post, thank you!  By no means do I think this is the best approach.  I am never complacent with how I teach anything so any advice is strongly recommended.  However, I do know that this is a better approach to learning about atomic structure with regard to evidence-based claims, scientific reasoning, and concept-building rather than simply telling students to read 3/4 of a page in a textbook dedicated to one of the most important subatomic particles in nature.  

Reflections on our first physics practicum

We are currently in the later part of our Constant Velocity Particle Model (CVPM) unit in my physics class.  So far, we have developed 4 models that only represent one particular type of motion, constant velocity.

• position-time (x-t) graphs
• velocity-time (V-t) graphs
• motion maps
• equation (Xf = Vt + Xi)

Throughout the development of these models, I constantly try to remind my students why it is that we're even building them in the first place.  Without going into too much detail in this post, my explanation revolves around the idea that in all fields of science, we rely on models to make predictions about reality and eventually better understand it.  If reality conflicts with our models that we make, then something must either be modified about the model or the entire model itself must be thrown out.  Models, if they are correct, essentially allow us to predict the future in addition to allowing us to deepen our understanding of how the universe works.  

So.....we put our models to the test!!  My challenge to them was short and sweet

Determine how long it will take for your buggy (car) to go from one position to another.  You cannot perform any practice trials.

I provided them with 2 bits of info and tools to help them gather data
Info:

• I gave each group an initial and final position (Xi and Xf)

Tools:

• Vernier motion detectors and a computer with Vernier's LoggerPro software

Based on our previous work with position-time graphs, several students caught on to the idea that maybe they should use the motion detector to come up with a position-time graph for their car.  Because they needed velocity to solve for the amount of time it would take to go from A to B, they knew all they needed to determine was the slope of their position-time graph.  Once that idea buzzed around the room, I told groups that they should probably perform 3-4 trials each in order to get a more accurate determination of their velocity.

Once each group had their velocity, I required them to make 4 things:

1. A quantitative position-time graph describing the motion of their car
2. A quantitative velocity-time graph describing the motion of their car
3. A quantitative motion map describing the motion of their car
4. An equation that is solved with their work shown so that I can see how their time was calculated

When they were finished with that, then it was time to test their models!  I connected 3 big whiteboards and made a position line that extended roughly 3m with intervals of .1m throughout.  Because groups had been given an initial and final position (each group had different ones by the way), they knew where to start their car.

The actual setup was simple.  Place your car at its starting position, place my iPad with the stopwatch up on one side of the position line, and I'll video tape the finish line in slow motion (120 fps) with my iPhone.  This allowed us to actually see what time the car crossed the finish line (their final position).  The results were great!!!  EVERY single group got within .6 sec of their predicted time and one group even made a PERFECT prediction!!  I've provided a couple samples below:

I took a screenshot so that you could see how much time passed by when their car crossed the line:

As you can see, their final position was 1.3 m.  What was their predicted time?????

5.80 seconds!!!!

This was so cool because not only was I excited about their result but I immediately saw the smile on their faces.  The members of this group were not your typical "do-gooders" in school and yet they made the best prediction in class!

A different group had a different car show below:

 Again, here is snapshot of their car crossing the finish line (2.7m) and its corresponding time

This group's predicted time was 4.21 seconds......awesome!!!

In the end, all 7 groups made awesome predictions and several of them were within .09 sec of their predicted time.

This practicum provided 2 important things:

1. It told us that our models accurately represent reality--at least with respect to constant velocity.  AWESOME
2. It was fun!  The kids had a fun time gathering around the whiteboard track and closely watching their car make its run.  Once groups had gone, they stuck around and watched other groups and it sort of naturally became a competition to see who made the best prediction.

This was so cool because it gave my students an opportunity to learn science by actually doing science.  Gather your data, make your models and test your models against reality.  Boom!

I will be doing another practicum next week where I give each group a specific time interval and an initial position and they have to tell me (based on their models) where their car will be at that time.  Can't wait to see the results!

Why I always ask my students to provide evidence

Without going into much philosophical detail regarding my take on the purpose of science education and the pedagogy that goes with it, one of the most important things I want my students to take with them in their life beyond my classroom is this:

Claims made by yourself or by others can be treated as dogma until you or the people making the claim provide evidence to back it up.  Until then....stay skeptical.

The point is simple and has practical uses in an infinite number of scenarios.  Just a few I can think of: (note: none of these claims are thought of to be necessarily true--they are just claims I have heard or claims that I know others have heard)

• Doctor comes in and tells you that you have cancer
• You hear from a friend that your girlfriend is cheating on you
• The quality of education a school provides is based solely on the funding it receives
• low-income students will naturally have low academic scores
• Climate change is simply not true
• African-Americans can jump higher due to subtle physiological differences
• Females are better at multitasking than males
• Students learn better when the teacher accommodates for different learning styles 
• water is made up of 2 atoms of hydrogen and 1 atom of oxygen

The list could literally go on and on.  Regardless of the claim, each one requires evidence to back it up.  For example, it may very well be true that when the doctor tells you that you have cancer that means you ACTUALLY have cancer, but we all know that no one is going to simply accept a life-threatening illness without SOME sort of evidence to back it up.  It's not that I don't trust the doctor and it's not that I don't trust the the people who make the claim.  It's the fact that ALL claims about reality require evidence, otherwise you're simply accepting things based on faith.  

So what's the last straw that broke the camel's back that prompted me to write this?

The other day, in my high school chemistry class, we were trying to determine the thickness of aluminum foil.  In order to do this, we needed to use our newly-derived equation from a mass vs. volume graph.

Density = mass / volume

Along with this, we needed to use an equation for volume:

Volume = Area * thickness

To solve for thickness, you need to know the area of the aluminum foil square and its volume.  Area was no big deal, simply measure length and width and multiply them--cool.  However, the problem arose when my students went to solve for volume using their original density equation.  Keep in mind that I gave them the density of aluminum (2.7 g/cm^3) and they found mass on their own by putting it on a scale.  When solving for volume, EVERY single lab group did the following thing:

Hopefully you can see the problem with this.  So how does this tie in with what I've been saying about providing evidence for claims?  Let me continue...

After giving a brief "algebra lesson" I tried to get the students to understand that you simply can't do this when trying to get the denominator by itself.  So why did a bunch of 11th and 12th graders make a basic 8th grade algebra mistake?  I think it was due to the years of mindlessly knowing that they can multiply the denominator by itself to get rid of it.....so why not carry the same logic to the numerator?  Then this stupid thing came up......

I can't tell you how much I hate something like this.  Any teacher of math or science has seen this and I absolutely hate it.  It totally promotes a "no thought required" approach.  The claims it makes are simple:

density = mass / volume

mass = density * volume

volume = mass / density

In this case, all claims provided by the triangle are true.  But the reason they are true IS NOT because I, as a teacher, showed you this little triangle "trick".  They are true for very basic mathematical reasons!  In fact, if I really wanted to, I could provide a graph which plots density vs. volume and show them how to calculate the area under the curve and literally show them where something like mass = density * volume comes from.  No matter the case, you can use proven rules of algebra to solve for ANY of the variables.  

Interestingly enough, when I showed my students this triangle, their faces lit up and it was like I had given them a brand new present.  Kids love it when you show them procedural or algorithmic ways of doing something--because it requires very little (if any) thought.  However, if I require to you derive the density formula from a mass vs. volume graph (which we did) and then algebraically rearrange that equation to solve for any of the variables....I've asked too much of you.  

It's not a matter of capability either.  EVERY single one of my students is fully capable of doing all the things mentioned right above.  I just don't want them to accept the fact that mass = density * volume or volume = mass / density just because they heard it from a teacher.  I want them to know it because they can prove it using their own reasoning skills along with the math skills we have taught them.

Finally, the last thing I got into with my class as we took a little detour from chemistry class.  I asked them, "what is pi?"  Immediately, every single one of them responded with, "3.14159 blah blah blah".  Some of them even know something like 7 decimal places....impressive!  But then I asked them, "how do you know this is number or, better yet, where does this number even come from?"  Not a single student had the slightest clue.  They had been taught this number since they were young and not a single teacher had managed to take 10 minutes to allow them to plot a circle's circumference vs. its diameter and calculate its slope (which is the value for pi).  "That's where this number comes from!" I said with a smile.  They weren't too amused.  By the way, it's not their fault....I didn't know this until I was 22 for the same reasons that they don't know it at their age of 17 and 18.  

Do I really care THAT much that kids know where the value of pi comes from or that mass = density * volume?  No....but don't miss the point.  If we consistently leave out room for the students to naturally use their reasoning to investigate WHY things are the way they are or HOW things happen and just simply tell them the facts, then we as teachers are no different than a Google search.  One of the cornerstones to a successful scientifically-literate democracy of people is the ability to reason.  If we willingly inhibit this ability, we are not only hurting our students in terms of inhibiting growth of their own thinking skills, but we are robbing them of a much deeper understanding of the amazing universe around them.  

Reflections on Ball Bounce Challenge

About a week ago, I posted a quick bit on the benefits I come across using Twitter to expand my profession learning community.  This particular post revolved around the idea of actually doing some physics the first couple days instead of doing the routine syllabus check and other typical 1st day "to-do" things.  While glossing over some potential activities, I had come across Frank Noschese's blog which included a fun ball bounce challenge activity with a high-speed camera.  After consulting with Frank via Twitter about the logistics of the activity, I decided to give it a try.

The first day went a little something like this:
In front of me are several balls.  As you can see, some are tennis balls and some are golf balls.  It shouldn't be much of a surprise that when I bring each ball up and drop it, the ball bounces back to a certain height.  Each ball bounces higher the higher I start it and, as you can see, the golf ball appears to have more "bounciness" to it.  We aren't going to concern ourselves with WHY this happens right now--that's for a later time.  However, we are going to use this phenomenon to collect some data and try to make some bold predictions.  
I have a very specific goal I want each group to try and achieve: start the ball at the appropriate height so that it bounces back up to a target height that I have already designated for you.  Keep in mind that you will not be given any practice rounds and you will not be told the height I want your ball to reach until we are ready for the challenge itself.  You and your group members must decide on how you are going to do this......SO GO!

At this point, groups got their balls (tennis or golf) as well as a meter stick (or 2) and I quickly began to see a variety of things happen.

• some groups simply dropped their ball against a meter stick and "eyeballed" its bounce height
• some groups dropped their ball and, using their iPhone, recorded its bounce height so they could view it later
• some groups only dropped the ball once and decided that one data point was good enough
• 1 or 2 groups really didn't know (or maybe care) what they were doing and just sort of bounced the ball a few times 

From my perspective, I thought all of this was interesting for a couple reasons:

1. It gave me insight toward how students value data.  Is one data point good enough or should I have more?  How accurate do I need to be and are there measuring tools or techniques that will allow me to attain more accurate data?
2. It also gave me insight as to who already sort of "gets it."  One quarter of my class qualifies for special education and I have several others who have demonstrated poor academic skills in the past (based on either already having them or simply hearing it from other teachers).  This is not to say that "teaching this class physics will be impossible" but it does have a profound effect on the extent to which I can assume certain skills my students have as a teacher.

We spent the entire first period, which just so happened to be a short day due to an earlier school assembly, collecting our data.  I assigned a number to each ball so that they would have the same ball the following day when attempting the challenge.

The second day:

I told the students I wanted them to have their ball bounce to a height of approximately 62 cm.  This was essentially the height of two lab stools.  As I walked around the classroom trying to get some insight as to how they were going to determine their starting height, I noticed the following methodologies from the students' perspective:

1. "Based on our data, the ball seems to bounce to a height that is about 85% of its original height.  Therefore, we're just going to calculate the original height so that 85% of it is 62cm."
2. "We found that our ball loses (some amount) of inches in height for every 1 foot we bring it down"
3. "We know that the ball has to start somewhere above 62 cm so we are just going to sort of eyeball it and hope that we come close"
4. "Our data shows that for every 10 cm we raise the ball, it bounces about 7 cm.  So we will try to use that so it bounces to 62 cm"

Again, I didn't really care how the students went about collecting their data and how they were going to use that to make the ball bounce to the target height.  The physics behind this activity is actually pretty cool and fun but it has its own place in the course down the road.  What was cool to me was that when given the freedom to develop their own experimental procedure, students sometimes come up with cool and creative ways to achieve the objective.  Sometimes ways that I would have never thought of before!  This can also go the other way too.  If given the freedom to choose, some students will essentially do nothing and any nudge I try to give them in the right direction will sort of just go right through one ear and out the other.  But that's a different story.

So what did the results of the challenge look like?

• As you will see in the videos, I placed a meter stick between the two stools.  I tilted it upright so that the broad side was facing the camera.  I told the students that if they got any part of their ball level with the meter stick, they succeeded in the challenge.  Because this was for fun, I thought it might allow some room for error.  Winners got to reach into a bag of mini Twix and take a handful.  I ended up going through 3 bags!!  All very large hands from teenage boys....

Winner

Winner

Winner

As you can see from the videos, some are pretty good and some went just went horribly wrong.  However, those that either won or got really close all had one thing in common: they had a plan that allowed them to collect enough data and come up with some sort of way to use that data to make a prediction.  It was their first attempt at using models to make predictions!

Overall, the activity was fun.  The students had a good time watching the youtube videos as a class and seeing who actually won.  It was easy for me to record the videos and quickly upload them to my youtube channel that same class period.  I will add a few new things to the activity next year so that each group provides some sort of data and each group makes a whiteboard that shows their methods as well as data.  This activity was really cool and I'm sure the students appreciated not having to spend yet another class period listening to their teacher read the syllabus :)