Summary

In this lesson, students first observe a flame test demonstration conducted by their teacher, and hypothesize about the identity of an unknown sample. Then they make connections in their understanding as they are tasked with building a prism, researching about wavelengths, and creating a model of electron energy levels.

Grade Level

High school

NGSS Alignment

This lesson will help prepare your students to meet the performance expectations in the following standards:

• 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.
• Scientific and Engineering Practices:
  • Developing and Using Models
  • Engaging in Argument from Evidence
  • Obtaining, Evaluating, and Communicating Information

Objectives

By the end of this lesson, students should be able to:

• Hypothesize about the composition of an unknown by observing flame color.
• Build a prism and demonstrate the splitting of light.
• Determine the wavelengths of visible light.
• Create a model of atomic energy orbitals and illustrate electron energy level transitions.
• Calculate the energy of the photon emission.
• Develop a presentation.
• Explain the relationship between color, wavelength, and electron orbitals.

Chemistry Topics

This lesson supports students’ understanding of:

• Atomic Structure
• Atomic Spectra
• Energy
• Electromagnetic Spectrum
• Visible light spectrum
• Electron energy levels
• Photon emission

Time

Teacher Preparation: 30-45 minutes

Lesson: ~2-3 hours

Materials

Day 1: Live Demo

• AACT Flame Test (Rainbow Demo) Resource
• 7,100 mL beakers
• Wooden splints (number depends upon how many times the demo will be performed)
• 1 Bunsen burner
• 1 Striker
• 50 mL of 1.0M Barium Chloride (BaCl₂) – Note: Barium chloride is highly toxic. Do not ingest the salt or solution.
• 50 mL of 1.0M Calcium Chloride (CaCl₂)
• 50 mL of 1.0M Copper Chloride (CuCl₂)
• 50 mL of 1.0M Lithium Chloride (LiCl)
• 50 mL of 1.0M Potassium Chloride (KCl)
• 50 mL of 1.0M Sodium Chloride (NaCl)
• 50 mL of 1.0M Strontium Chloride (SrCl₂)
• Deionized water
• 250 mL beaker or plastic or cardboard cup half full of water
• Class copies of the visible light spectrum chart showing wavelength and frequency values
• Safety lighter
• Safety Goggles

Day 2: Build and Explain:

• Plastic bottles or glasses
• Water
• *Materials may vary

Day 3: Model the Idea

• Cardboard
• Markers
• Pegboard
• Pencils
• Marbles
• *Materials may vary

Day 4: Create a presentation

• Presentation platform (PowerPoint, Prezi, Video, etc.)
• Device

Day 5: Showing Off

• Virtual Meeting Place (Zoom, Google Hangout, etc.)

Safety

• Wear proper personal protective equipment when preparing and working with solutions. Safety goggles and lab apron are required.
• Barium chloride is highly toxic. Do not ingest the salt or solution.
• If the demonstration is conducted in-person rather than remotely, students should wear proper safety gear during chemistry demonstrations. Safety goggles and lab apron are required.
• Always use caution around open flames. Keep flames away from flammable substances.
• Always be aware of an open flame. Open flames can cause burns. Do not reach over it, tie back hair, and secure loose clothing.
• Wash hands after handling materials used to prepare for or perform this experiment.

Teacher Notes

• This lesson plan was designed as a meaningful lab experience for student while in a homeschool environment. To learn more, read the associated article, Creative Ways to Conduct Traditional Labs in a Homeschool Environment, published in the November 2020 issue of Chemistry Solutions.

Day 1: Live Demo

• Background: When energy is added to an element, it causes electrons to occupy higher energy levels. Since this configuration is not as stable as a lower energy configuration, the electrons will fall back to a lower energy level. When this happens, a photon of a specific wavelength is ejected. The color produced depends on the wavelength. This phenomenon can be observed by igniting the metal salts and viewing the color of flame that each metal salt produces.
• I encourage you to use this very safe procedure of the Flame Test for your demonstration.
• Teachers should always practice the demonstration before doing it for students.
• Video Samples: Before you perform the live demonstration, create video(s) of unknown sample(s). Record either an metal salt or a color flame candle as the unknown (or multiple unknown samples if needed). Make certain to clearly label the video as the “unknown”.
• If you use Google docs with your students, share the video in a document and they can easily access it and record their digital notes on the same document.
• Ask students to hypothesize about the identity of each flame, and why each of the flames are a different color. Allow students multiple ways to express their answers. For example, students could have the option to write their hypotheses on the Google doc or record a Flipgrid video.
• The Student Section of the Flame Test (Rainbow Demo) includes a data table where students can record their observations and calculate wavelength (used in Day 2).

Day 2: Build and Explain

• For this part of the lesson, students will build a prism and explain why the white light entering the prism is separated into different colors upon exiting the prism. The students should discover that as the white light is refracted by the prism, the different wavelengths that comprise white light will be refracted at different angles. Thus, when the light exits the prism, it will be divided into varying wavelengths. Ask students to assign a range of wavelengths for each color that exits the prism. The bulk of the research for this activity should fall on the shoulders of the students. Do not give them too much information – let them discover it for themselves!
• The students need to document the process of building their prism, testing their design, recording their results, and researching the wavelengths associated with each color.
• I suggest that teachers allow students the freedom to document the building process in their favorite format (or a combination of). Examples include, recording in a science journal, providing links to video recording of themselves documenting the processes, illustrations, photos, etc. All students should provide a photograph of their own prism in their results.
• Encourage students to be creative and quirky.
• Students should be able to assign the following wavelength ranges to these colors (Wikipedia).

Violet	380-450 nm
Blue	450 – 485 nm
Cyan	485 – 500 nm
Green	500 – 565 nm
Yellow	565 – 590 nm
Orange	590 – 625 nm
Red	625 – 740 nm

Day 3: Model the Idea

• Now that students have seen how light can be divided into its components, it’s time to develop some intuition about why there are different wavelengths. For this part of the lesson to be effective, the students need to have prior knowledge of electron orbitals and energy levels.
• Background: When an atom is introduced to energy in the form of light or heat, some of the electrons in that atom briefly absorb the energy and jump up to a higher energy level. Because this is not the lowest, most stable energy state, those electrons eventually lose that energy and “fall” back down to a lower energy level.
• The lost energy is emitted as a photon of a particular wavelength. The value of the wavelength depends on the distance between the energy levels, or how far the electron “fell.” The more energy that is emitted in the form of a photon, the lower the wavelength (energy and wavelength are inversely proportional.) Remember that are restriction on which orbitals electrons can transition to because of the conversation of angular momentum, but this might be too deep a topic to dive into.
• However, students should know that electrons can only transition between s and p-orbitals, p and d-orbitals, and d and f-orbitals. (For example, an electron can transition from a 4p energy level to a 2s energy level or a 3d energy level, but not to a 3p energy level.)
• Ask students to construct a model showing the process of an electron absorbing energy from heat (as in our flame test demo), jumping to a higher energy level, then “falling” to a lower energy level and shooting out a photon. They might begin with an electron orbital diagram and add illustrations, levers, marbles, styrofoam balls, or anything else that would be useful. They might also try and construct a 3D model of this process, which might even include springs, levers, fulcrums, platforms, etc. (Example of model shown in photograph).
• Make sure the students know that they will be explaining/demonstrating their model to their peers.
• The simulation, Exciting Electrons might be helpful to show students after they have completed.

Day 4: Create a presentation

• Students should create a presentation that encompasses all the activities for the week. This is where they can show off their work, creativity and understanding of the topics. Encourage the students to use their choice of presentation platform as long as it can be shared digitally. If students shy away from online tools such as Prezi or PowerPoint, they can create a physical presentation and video themselves walking their viewers through their creations. Offering multiple ways of demonstrating understanding will help them focus on the idea rather than the deliverable.

Day 5: Showing Off

• This is the day your students will show one another their presentations. You can post video walkthroughs of the presentations on your class webpage or you and your students can meet over Zoom and take turns sharing screens.
• Each presentation will be unique and full of good ideas, and each presentation will likely have room for improvement. Remember to focus on the ideas that are presented rather than the artistic license that has been taken.