Using Molecular Modelling Kits to Predict, Explain, Observe, Explain the Relationship between Chemical Formulas and Molecular Shapes – Post #43

 In my grade nine applied science class the students are typically very good at both interpreting a chemical formula and in building molecular models, using the tradition ball and stick kits. However, when it comes to the higher order thinking required to add or subtract an atom from a molecular compound they are not able to visualize how the molecular shape is changed. This semester I decided to use the Predict, Explain Observe, Explain (P.E.O.E.) model that is encouraged by Smarter Science to help the students move forward in their thinking.

Prior to performing this activity the students were taught how to deconstruct a chemical formula. That is, they could articulate that H₂O (water) was a molecule composed of two hydrogen and one oxygen atom whereas H₂O₂ (hydrogen peroxide) was a molecule made up of two hydrogen and two oxygen atoms. Although the students were familiar with the Periodic Table and knew that families or groups represented the vertical columns and atoms in the same family shared chemical and physical properties they were unable to interpret the number of valence electrons each atom has and how this influenced chemical bonding.

1.      Initiate and Plan

To engage the students in this activity I began by distributing the molecular model kits and explaining the reason that different coloured balls had a different number of holes. Together we observed the colour coding of the atoms, their position on the Periodic Table, the number of holes drilled into the model atoms and the number of valence electrons they each had. Most students were very confused at this stage.

2.      Perform and Record

In pairs, the students found the correct coloured atoms to build one molecule of water and built it. It quickly became apparent that unless the oxygen atom was placed in the center the molecule could not exist. It was further observed that the molecule was “bent” or angled, and could not be a straight line.

I distributed the P.E.O.E. template to the students and had them predict how the look (shape, geometry) of an atom of H₂O would change if one atom of oxygen was added, making H₂O₂. When asked to make this prediction on paper most students just drew an oxygen atom to the oxygen atom that was central to the water molecule.  They did not take into account that there were insufficient valence electrons to make this possible. This concept appears to be too abstract for these learners at this stage of their academic career. 

Once the students had completed box 2 of their P.E.O.E. template they were then instructed to build the H₂O₂ molecule. When given the hands-on model to build they immediately realized that their predictions were incorrect, took their water molecule apart and constructed the correct molecule for H₂O₂. 

3.      Analyze and Interpret

When the students compared their models of water to that of hydrogen peroxide they were able to contrast their shapes (bent vs. straight line)

.4.      Communicating

Students used the PE.O.E.  to communicate what they had learned about the relationship between the chemical formula and the look of the molecule. They went on to build a number of various molecules. Initially I supplied them with a list of chemical formulas to build and draw. Subsequently they built molecules ad hoc and determined their chemical formulas. Lots of authentic learning occurred, everyone had fun and my learning outcomes were achieved.

What learning outcomes?

From Strand A of our Ministry document – Scientific Skills and Investigation we demonstrated scientific investigation skills (related to both inquiry and research) in the four areas of skills (initiating and planning, performing and recording, analysing and interpreting, and communicating) (A1). We also selected appropriate instruments and materials for particular inquiries (A1.2). And from the Chemistry unit we demonstrated an understanding of the properties of common elements and simple compounds, and general features of the organization of the periodic table (C3). 

What strategies do you use to help these learners understand that importance of chemical bonding in molecular geometry?

11. Chromatography – Pure Substances and Mixtures

This Friday we had a “snow day”, which means the amount of snow, or in this case freezing rain, that fell overnight rendered the roads too dangerous for sensible people to risk their lives driving to the school buses are cancelled. In our school boards the school buses get canceled but the schools never close, so all the teachers must report for duty! In addition, because it is a “regular school day” we must all carry on with activities that are directly related to the curriculum, not watching movies or playing games. (Unless they are curriculum related, of course.)

In my case, I view these “snow days “ as opportunities to do some fun labs, that I might not otherwise do, so we get the best of both worlds -- a learning activity that is related to the curriculum but a fun activity. I want to make sure that the students who show up for class have an enjoyable learning experience but those who did not make it into school are not left behind in the dust.

Our grade nine class is deep into the chemistry unit at present. We have mastered the concept that matter is subdivided into pure substances and mixtures, etc. So we took the time of Friday to do a simple Smarter Science chromatography lab to explore mixtures and pure substances further.

1. Initiate and Plan = ENGAGE

I started the class by explaining chromatography to them in real simple terms. I modelled how I could put samples on a start line on filter paper and place the bottom of the paper into a beaker with a small amount of water in it. The water moved up the paper by capillary action dragging the components of the sample with it. Before class I had prepared several chromatography papers which I dried and showed to the students. In all cases the samples I used were dots of ink from a variety of markers that I had lying around my classroom. When we examined the finished chromatographs we could observe either one solid coloured line or a line that split into a prism of colours. I posed the questions “Which inks made solid lines and which inks split into a prism of colours?” the students were quick to assert that if more than one colour could be seen in the chromatograph the ink must have been a mixture whereas chromatographs with a solid colour must have been a pure substance.

I then distributed the Smarter Science starburst diagram so we could determine all the variables that could be controlled or tested for in a similar experiment that the students would run. We brainstormed six items.

1. The amount of time the chromatograph was run

2. The amount of liquid placed in the bottom of the beaker

3. The size of the ink dot

4. The colour of the markers

5. The brand of the markers

6. Size of paper

The students discussed the list of variables with their partner to decide which one they would test for. They moved the post it note with their dependent variable to the head of the fish diagram. The other post it notes became their independent variables and were moved to the “bones of the fish diagram.

2. Perform and Record = EXPLORE

The partners continued to design their experiments by planning the values to give each on the independent variable, ie. How long to run the experiment, how much water to use, what brand of markers to use, etc. Once they had determined their variables they began experimenting.

Yet again I had the pleasure of watching student’s experience a lab technique for the first time and react in wonder. When the inks actually began running up the paper they were amazed! This short video clip illustrates the joy experienced by one group as they produced a rainbow.

3. Analyze and Interpret = EXPLAIN

The students analyzed their chromatographs to determine if the various inks they used were pure substances or mixtures. They compared their results with each other while classifying their inks.

4. Communicate = EXTEND

Because it was a snow day and these students had actually made the effort to come to school I allowed them extra time to reflect on this lab and play with the technique. I had them explain their results to me orally and write a one sentence conclusion.

N.B. The students were pleased that although they had come to class on a snow day they “didn’t have to do any work” and were allowed to experiment instead! After the lunch break we blew up a gummi bear and a sour patch kid (two different types of candies), in two separate explosions, using potassium chlorate. We followed up with a discussion of which one caused the greater reaction therefore contained the most reactant (sugar). Then we played a Periodic Table game using the smart board wherein they had to identify elements by the number of orbitals and outer most electrons they contained. Lot’ s of fun! No work! And even the administration is happy!

Posting Ten -- Discovering Physical and Chemical Properties

We’ve had a few more signs that winter is coming to Ottawa – a freezing rain storm last night resulted in a number of fender benders, including people smashing into ambulances and pedestrians falling down and breaking their bones. Yet in the classroom we persevere, the courses march ever onwards, we are over half way through the first semester now, midterm report cards have gone home, time marches on!

This week the grade nine applied science class started the chemistry unit (aka Exploring Matter) which lends itself to so many fun labs. It is important for the experienced teacher to remember that what has become ho-hum for them is new and exciting for the grade nine learner, who is often experiencing doing chemistry “in a real lab” for the first time! To that end I always make sure that the student has as authentic an experience as possible, which is easily accomplished if they wear safety goggles and use “real” scientific equipment instead of paper cups and plastic spoons. That being said I am fortunate to have an actual lab with real equipment, but the same results can be achieved using materials that are at hand.

I have taught the concept of physical and chemical properties many times and have always used a cook book lab as a follow up to the theory. This year I wanted to use the Smarter Science technique of having the students plan their own lab so I designed a table for them to use wherein they both designed the procedure and recorded their observations.

1. Initiate and Plan = ENGAGE

The students were instructed to test hair, magnesium and brom thymol blue for physical and chemical properties. The properties to be tested for were identified on the table provided.

Since we had already done a couple of labs this week the students were familiar with the equipment we have available and where it is kept. They were instructed to come up with a method of testing for each of the following physical properties: colour, lustre, solubility, density and texture as well as the chemical properties: combustibility, reaction with oxygen and reaction with acid. Only when they had filled in the middle column of the handout (above) were they allowed to gather the needed materials together.

2. Perform and Record = EXPLORE

The students’ favourite part of every lab is experimenting and recording and, as usual, they were enthusiastic participants. Although they had candles to test for combustibility the flame did not get hot enough for two of the groups to experience success with the magnesium so I brought them up to the fume hood where I have a Bunsen burner and let them use it. Wow!

3. Analyze and Interpret = EXPLAIN

In order to help the students analyze their results I posed the question “what is the difference between physical and chemical properties?” This question prompted them to review their table and analyze the techniques they had used when testing for physical versus chemical properties.

4. Communicate = EXTEND

Upon reflection most of the students were able to explain that physical properties could be detected using one of the five senses but chemical properties required a reaction, which did not seem to be reversible.

Why I love teaching!

My own favourite moment during this lab was when my shy ESL student completed her lab then came over to a group of yahoos who were dithering around , asked them if they had reacted acid with their brom thymol blue yet and proceeded to do it for them. Wowie - Zowie! They thought she was magical when the solution turned yellow. They quickly got their act together to test everything themselves. Seriously, it was beautiful! This girl had never even spoken to these rowdy boys before and now she had not only spoken to them but demonstrated her learning to them! Major props all round!

What about you? Why do you love teaching? Have you tried using the Smarter Science framework yet? Is this blog helpful to you? Please leave us a comment.