This lesson lays the groundwork for HS PS 1-1. This Performance Expectation asks students to Use the periodic table to predict properties of elements based on patterns of valence electrons. However, the middle school standards do not contain a need to instruct on the composition of the atom, or atomic models. Therefore I like to begin the course with a one day walk from the past, helping students connect their real world experiences with matter to the idea of atoms.
My students come from multiple school districts, and their prior knowledge in this area is varied at best, so the card sort below also gives me a quick formative assessment to their understanding of the concept of matter. The day before we discussed the terms: proton, neutron, electron and atom to begin to build our common course vocabulary. It is hoped that seeding the term "atom" the day before will result in students thinking about atoms during the card sort.
For the demo you need the following per class section:
To clean up the demo, a trick I learned is to boil the solution. Lead (II) iodide is much more soluble at high temperatures. This is an easier way to get it out of the flask and into a beaker where you can filter out the precipitate at room temperature and scrape clean any residue in the beaker.
I begin the class with students in groups of four to conduct a card sort. The sort is of 26 terms focused around the question "Is it Matter?" from NSTA Press's Uncovering Student Ideas in Science, Vol 1 #10. Copies of the student sheet of this activity are also provided for each student to record their final results. I ask the students to sort the cards into two distinct groups: Matter and Not Matter.
While students are sorting, I circulate the class to see how students are sorting and what types of conversation they are having to perform the sort. I often allow students to make a third category at first -- "unsure" but push all groups to finish with all the terms sorted. The most important part is for the groups to articulate their rule in determining what is and isn't matter.
The most common misconceptions are around gases such as air, steam, smoke, and oxygen; as well as fire and stars. Students tend to think of matter as tangible, and forget that you can feel air via wind flowing. Oftentimes students will classify fire as matter rather than an event or reaction because they know it involves matter, and mistakes that for it being matter. Stars are experienced as light, and depending on prior knowledge -- may not be aware that they are element factories that contain vast amounts of matter.
I have the groups share their rule, but not necessarily their final sorting. Keywords from the rule are recorded on the board or screen via document camera. We look for commonalities between definitions. If the class has come to an accurate consensus, we stop at their definitions. However, if there are multiple inaccuracies, I probe deeper with the accurate groups asking them to explain how they arrived at their definitions. Once we reach a class consensus on the correct rule determining if something is made of matter, we are ready to move on. The most basic rule I will accept is that matter is made of "stuff" with the preferred term for stuff being atoms. If the class needs to see the final sorting of the terms I will flash it on the screen via document camera during our transition to the next part of the lesson.
The NSTA activity is written as an individual student activity. I prefer it as a group experience to help build student comfort in interaction, debate and discussion. Student disputes over what is and isn't matter and the rules governing classification will model the upcoming section of the lesson regarding scientists and philosophers disagreeing even when arguing from evidence.
Now I have students get out their binders and open to a clean page while projecting the first slide of the PowerPoint -- Philosopher Grudge Match. As this is the first time using PowerPoint for the year, I prefer to see how students choose to take notes before imposing a structure. During the first binder check I will look to see if students copied the slides word for word, if they recorded bits of the class discussion, or wrote additional questions. Based on the binder check, I will begin to introduce note taking strategies as needed.
We begin chronologically with the Greek idea of the four elements -- Earth, Wind, Water and Fire -- with comparisons to our definition of matter from the card sort. We proceed to Democritus' idea that everything is made of a invisible, indivisible parts or "atomos" for indivisible. Next is the introduction of Aristotle, who many students have heard of. Aristotle ridiculed Democritus, arguing that matter is continuous and made of the four traditional elements. I then ask students- based on what they can see, who wins? Aristotle wins hands down based on our observable universe. I follow this up with "What did we need to improve our observations?" where students point out technology. We then talk about basic technology that changed science -- microscopes and balances. We then discuss how the discovery of the cell and organelles begins to make Democritus' ideas seem possible again. Then we discuss the most important invention to early chemists -- the balance.
I then pause the presentation to demonstrate conservation of mass. For this I utilize the lead (II) nitrate and sodium iodide "yellow snow" precipitate reaction.
Pb(NO3)2 (aq) + 2 NaI (aq) -> PbI2 (s) + 2 NaNO3 (aq)
The setup, which can be prepared before class, consists of a small test tube containing 10mL of 0.1M lead (II) nitrate in a stoppered Erlenmeyer flask containing 20 mL of 0.1M sodium iodide. I use the document camera to show the balance before the reaction, and then ask students to predict what the mass will be after the reaction. Then I invert the flask (or invite a student to come up and do so) to mix the reactants and make the yellow lead (II) iodide precipitate. Before placing the system back on the balance, I ask students to predict the mass again- many students will misconceive that the solid will increase the mass. We then mass the system again and confirm that the mass is the same.
From the demonstration, we expand or definition of matter to being made of invisible particles that can rearrange into new chemicals. This concept of molecular rearrangement and conservation of mass should be prior knowledge from middle school, but is often still missing in my students. I then refer back to the PowerPoint -- to observe these particles, we can wait for improved technology, or rely on other means.
Ask students how they know if someone used too much body spray in the hallways. They will cite the smell most often. I use this to point out that humans are sight dominant, but that other senses can help in making observations. I then ask them how they can tell if someone is coming around the corner on a sunny day. Students reference sound, and shadows (hence the inclusion of the "sunny day"). Shadows are an indirect observation of an object. I then explain that when technology is lacking for direct observations, we have to rely on indirect observations, which can be more challenging.
Next, I ask someone from each table (group of four) to come up and get 4 lab papers and 4 obscertainers. Obscertainers are opaque, numbered petri dishes with a metal BB and a set of walls inside. I will draw a possible internal configuration on the board so students have an idea of what they trying to do. I then ask students to try to identify the internal configuration of the four obscertainers at their table without opening them. Students use their data sheet to record what they think the internal configuration is.
After about 6-7 minutes, I ask students to share their frustrations. Then I share the correct configurations and allow them to try to confirm it now that they know the correct configuration. We also quickly explore whether students in the same group had different conclusions from the same evidence before wrapping up the lesson.
We close the lesson with a 3-2-1 on a half-sheet of paper I provide and have copied. Students will record:
This exit ticket is required before leaving the classroom.
I like the 3-2-1 format for lesson closure. Often times I will include in the "2" line a chance for them to write down two questions they have about what they learned today. This will provide a snapshot formative assessment to adjust and guide the next lesson.
Here are two successful student examples.