Day 2: Colors of the Rainbow

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Objective

SWBAT explain our current understanding of the atom citing evidence from experiments.

Big Idea

Students connect knowledge about electrons and atomic structure to how fireworks get their brilliant colors!

Introduction

This lesson addresses the NGSS HS-PS1-1, use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.  The goal of the lesson is to provide evidence that electrons exist and are located in different energy levels with specific energies.  This is aligned with the NGSS Disciplinary Core Idea (DCI) PS1.A (Structure and Properties of Matter): “each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons”. 

In this lesson students explore the structure of the atom using the NGSS Science Practice 3: Planning and Carrying out Investigations.  This lesson is an extension of the previous Day 1:  Colors of the Rainbow lesson.  

Students conduct a flame tests of two unknown salts and identify them using data from day 1. Students then learn how the light is generated by electron excitation. Finally, students elaborate on what they learned and apply that information to a real world application, fireworks.  This lab demonstrates evidence that subatomic particles are present within an atom and further builds a foundation for exploration of HS-PS1-1.

The Cross Cutting Concept (CCC) that is illustrated in this lesson will be Patterns, as it is an extension of the previous lesson on the Bohr’s model.  Patterns are illustrated in this lessons as students continue to see that as elements changes so do the number of electrons.   This can be seen by the various colors that are emitted as electrons move from an excited state back down to a ground state during the flame test.  

Homework Check-in

5 minutes

My homework check-in is a very quick process at the beginning of class as students are getting their goggles and aprons for the day’s lab investigation. Right after the bell rings I ask students to take out their homework which was to complete the day 1 post lab questions and data table, so that I can check it in.  I then ask them to get their goggles and aprons.

When checking in their homework I am only looking for completion and either put a + for completed, a check for partial completion or a – for not completed.  I like to use stamps that way they can’t change a – to +.  I find this to be an effective strategy for checking in homework.  I do this to make students accountable for completing their homework on time and as preparation for the day’s lab.  Later on I can look at the check-in marks after they have turned in the completed assignment and score them with full credit or partial credit depending the quality of their answers.

When checking my student responses to the day 1 post lab questions I look for them to understand that when electrons gain energy they can move from a ground state to higher, excited state of energy and as they move back to the ground state the releases of energy is emitted as wavelengths of light.  The visuals from the lab should provide them with evidence that electrons exist in various quantities depending on the element and contain different levels of energy.

Elaborate (lab)

20 minutes

This part of the lab is an extension from day 1: Colors of the Rainbow (Flame test lab) where students will elaborate on their findings.  In day 1 students should have created a data table containing the names of the salts and the color emitted from each salt while in a flame. The students then use this information to identify two unknown salts that I give to each group. 

I remind students that in the previous day's lab they dipped moistened splints into salts and put them in the flame, but in this part of the lab the unknowns are one molar salt solutions (see here for simple directions on how to make 1 molar salt solutions) that have blue dye added to them. See the reflection for further explanation.

I let students know they can use the solid salts if they want to make a comparison, but I instruct them that they need to be careful not to contaminate the unknown solutions.  I also instruct them that it is important to write the correct number of the test tube along with the unknown name because if they don’t put the number down I have no idea what they have. This may seem intuitive, but it’s amazing how students forget a simple step.  Finally I let them know they will have to read an article on fireworks as extension to the lab which can picked up from my desk after I check lab stations for proper clean-up.  This process is the same as the previous day's lesson.

While the students are working on the unknowns I circulate around the room making sure that they are still following the proper lab procedures from day one and look to see if they have the proper colors in their data tables.  If they don't, I encourage them to try burning one of the solid salts first so they can make a comparison. 

After about 15-20 minutes, upon completing the unknowns, I instruct students to return them to my desk and pick up a copy of the ChemMatters article Fireworks! by Kathy DeAntonis.

I've attached a copy of the lab key and Colors of rainbow SW  If students were to struggle with answering the post lab questions it was with question number 2, 4 (day 1) and 9 (from day 2 Students sometimes have a difficult time attaching the right words with what they are trying to saying.  For instance students might know that energy is being absorbed by the atom, but not know how to say it is the electrons that are absorbing, and releasing it as they return to their ground state.  This problem may persist for a while, but as we move forward towards the periodic table and bonding, the concept and structure of the electron and the atom as a whole starts to get uncovered.

Elaborate (Firework Article)

20 minutes

As an extension to the lab I have my students read about fireworks. In the article Fireworks! my students read about how fireworks are made, how colors is emitted from excited electrons dropping to a ground state, firework safety and why chemistry is a part of pyrotechnics. 

This ChemMatters article is a great way to summarize the lab experiment because it attaches a real-world application to the to a lab investigation.  It also brings a literacy component to the lesson that is aligned with CCSS.ELA-LITERACY.RST.9-10.2. 

I cannot post the article but I have created a link to a website where you will be able to make copies for your students.  I recommend using ChemMatter, a American Chemical Society publication, as a resource.  It has excellent articles that cover a variety of topics and can help add a literacy component to your classroom.

After my students read the article they can finish the day 2 post-lab questions which contain questions about the lab and the article.  I let them know that the lab will be due the following day and there will be a short quiz that covers everything that we have learned to this point.  It will cover matter, atomic structure, Rutherford’s Gold Foil experiment, the Bohr’s model and the flame test.