Day 1: Colors of the Rainbow

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Objective

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

Big Idea

The Bohr model illustrates the presence of electrons which can be demonstrated by the different colors various metal salts produce in flame tests.

Introduction

This lesson addresses 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 they are located in different energy levels, in varying quantities.  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  NGSS Science Practice 3, planning and carrying out investigations.  This lesson is an extension on the previous lesson on Bohr’s model and let students investigate the presence of electrons during a flame test. 

The goal of this lesson is to have student understand through guided inquiry that electrons have energy and the energy released from atoms can be seen in the form of color.  This process illustrates 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.  

 

Engage/Warm-up

5 minutes

In this part of the lesson I let my students experience the process of triboluminescence, a fancy word for light being emitted when two particles are rubbed together.  I love this activity and so do my students. 

As students are entering the room I hand them each a prepackaged wintergreen Lifesaver and tell them not to eat it.  This instruction builds a lot of curiosity and sets the stage for the day’s lesson.  As the bell rings I let my students know that these are not normal Lifesavers they are special Lifesavers.  This again piques their curiosity. Then I ask students to grab a partner, open the candy and get ready to put it in their mouth.  I tell them that they need to be facing there partner as the bit down on the candy with their mouth open.  I then shut the lights off and have them bite down…

They are amazed that light is being emitted from their mouths.  It is not a lot of light, but enough for students to be amazed.  I then turn the lights on and ask them, "what do you think caused the light to come out of your mouth?"  Many students think that the culprit is friction, or chemicals, which is partially correct.  But with a little direction and refreshing about the parts of the atom, it can be narrowed down to the electron. 

I then ask students, "what color came from the Lifesaver?"  If they were able to see light after biting down on the Lifesaver, they usually correctly say "blue".  After this I ask the open ended question, "why was the color blue?" Responses are usually "dye" or "coloring".  I let them know that wintergreen Lifesavers are white and appear to have not dye.  This perplexes students.  Overall, the wrong answer is fine because it sets the stage for the Colors of the Rainbow investigation (flame test).  

Explore (Safety and procedures)

15 minutes

Safety (10min)

After curiosity has been established I hand out the Colors of the Rainbow Lab investigation and instruct my students to get their goggles and aprons.  The second order of business is to establish safety guidelines with my students.  I like to get students to do this because they are no longer my rules, but instead they become their rules and it starts to get them involved in the process of inquiry.  I get the process going by introducing them to the materials that are listed on the lab (see Colors of the Rainbow for list).  This provides them with a basic guideline for the safety rules that need to be set. 

After the materials are listed I ask students to give some rules that should be followed.  As they say them I write them on the board.  The list should contain:

  • Wearing goggles at all time…with a set of consequence if not follow: possibly point reduction or wearing goggles for entire non-lab period (the kids love this one!).
  • Apron must be worn in the presence of chemicals or fire.
  • Hair needs to be pulled back in the presence of fire.
  • No open-toed shoes
  • No horseplay
  • No eating
  • Be aware of flame at all times (Bunsen burner)
  • Dispose of waste according teacher instruction
  • Keep lab stations clean

I allow 10 minutes for this process. If the class does not mention one of these by the end of the discussion I will add to the list before moving on to the procedure.  This will take less time later in the year as more labs have been complete.

Procedures (5min)

This portion of the lesson is very brief.  I start out by going over the lab materials and procedures listed on the Colors of the Rainbow Lab.  While I instruct them on materials and procedures, I also demonstrate what to do.  I start out by demonstrating how to light a Bunsen burner since this is the first time they have used one.  I follow this up by showing them how to dip the moistened splint in the salt and place it in the Bunsen burner.  This shows them that something might have multiple colors, but they need to pick the predominant color (see colors list).  This is relatively simple, but if you have not performed this lab before I recommend trying it before you show the students.  This serves two purposes:  (a) for safety reasons and (b) it will show you the colors of each of the salts and prepare you for the lab.

I follow this up by explaining that they will have to create a data table.  I do not show them how to make one, as this process will be discussed and demonstrated as a post lab discussion, I just tell them what needs to be in it (which is listed on the lab handout) and that it is important to make careful observations.  I conclude the demonstration by letting them know they will have to  collect data (observations) and use it to identifying two unknowns on day two of the lab.  After completing the demo I let students begin the lab investigation

Explore (student investigation)

20 minutes

I give students 20 minutes to complete the investigation which is plenty of time to perform a couple of tests for each salt to ensure accuracy.  As they are working I circulate around the lab asking students what colors they see.  I do this to ensure that students are aware they may see blended colors, but need to focus on the main colors.  For example, for barium chloride students might see some red instead of green.  This is also a good time to look at the way they are making data table. 

At this point in the year you will see a variety of styles, but this is fine.  I let them take data any way they want and will address data table construction during the post lab discussion on day two.  This is a learning process that I believe is an important part of inquiry.

Elaborate & Evaluate

20 minutes

As students are finishing up the lab I let them know they must have a clean lab station before moving on to the Day 1 post-lab portion of the investigation. After students complete the lab investigation, I check there lab stations to ensure they are EXACTLY as they found them at the beginning of class.  On their lab sheets I will give them 3 points if they did an excellent job, 2 points for messy but eventually cleaned, 1 point for clean-up and not working on post-lab questions till the bell rings and 0 points for no clean-up.

I believe it is important to establish clean-up policies and post-lab policies from day one, so they are accountable for their responsibilities.  After they have received their clean-up points, they are able to work on their day 1 post-lab questions.  If they are not working on their post-lab I will deduct points.  These questions will be a foundation for day 2 and will be checked in first thing the following day.  

The goal of the post-lab questions are to get students to think about experimental error (question 1), review the structure of the atom via the Bohr’s model (question 3) and interpret from the lab data that electron can emit light when energy is absorbed and released (questions 2 and 4).  In future lessons students will be able to build on the information from this lab and connect it to principles of bonding, intermolecular forces and bond energy.