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Spectral Analysis and Energy Structures in Atoms

Written by: Gregory Kichton

School: High School

District: Cobleskill-Richmondville

Subject: Energy Structures

PLANNING THE LESSON

OVERVIEW:

In this activity students will use the visible line spectrum of hydrogen to create an energy level diagram for hydrogen. This will include levels n=2 through n=6. They will compare their results with an energy level diagram provided in their reference tables and explain the differences. They will repeat this process to produce an energy level diagram for an unknown element.

GOALS: (New York State Science and Technology Standards)

Standard 6 - Interconnectedness: Common Themes

Systems Thinking: Through systems thinking, people can recognize the commonalties that exist among all systems and how parts of a system interrelate and combine to perform specific functions.

Models: Models are simplified representations of objects, structures, or systems used in analysis, explanation, interpretation, or design.

Measurement and Scale: The grouping of magnitudes of size, time, frequency, and pressures or other units of measurement into a series of relative order provides a useful way to deal with the immense range and the changes in scale that affect the behavior and design of systems.

Standard 4 - Science: Physical Setting

3. Matter is made up of particles whose properties determine the observable characteristics of matter and its reactivity.

4. Energy exists in many forms, and when these forms change energy is conserved.

5. Energy and matter interact through forces that result in changes in motion.

OBJECTIVES:

The student will be able to correctly define the term bright line spectrum.

The student will be able to capture an image the line spectrum for that element and import that image into Scion image by following written instructions. (Optional Extension)

Given a line spectrum in Scion image, the student will be able to correctly measure the wavelength of the electromagnetic radiation and calculate the frequency and energy of that radiation.

Given the energies of the bright lines in the spectrum of hydrogen, the student will be able to construct an energy level diagram which corresponds to the energy transitions shown in the spectral analysis.

BACKGROUND INFORMATION:

RESOURCES:

Hydrogen and mercury discharge tubes, power supply, class set of student spectroscopes, computer with Scion image and Scientific Notebook software, metric ruler. If the students are going to capture their own images of line spectra then a precision spectroscope and digital camera (flexcam) with eyepiece adapter will be required.

PRIOR CONCEPTS:

At this point in the year students will have studied wave properties, quantum theory of light, structure of the hydrogen atom (Rutherford and Bohr models) and Bohr's three hypotheses.

Learning Cycle Activities:

EXPLORATION PHASE:

T will demonstrate proper use of student spectroscope.

T will pass out student spectroscopes.

S's will view spectrum of light from windows.

S's will compare continuous solar spectrum to that of florescent lights.

T will introduce concept of bright line spectrum.

T will ask S's about flame tests they performed in Chemistry class and link idea that certain colors are characteristic of certain elements. For example yellow for sodium.

T will ask: What colors are characteristic of Neon?

S's will observe bright line spectrum of Neon with spectroscopes.

CONCEPT INTRODUCTION:

Student will:

Sketch the line spectrum of hydrogen in their lab notebooks from observations made with the spectroscope. S's will record the wavelength of leftmost and rightmost bright lines.

Capture bright line spectrum of hydrogen with digital camera.

Save line spectrum in uncompressed TIFF format.

Start Scion Image, open line spectrum and convert to grayscale. (These steps capturing and conversion steps may be omitted and the students given the spectrum in grayscale to work with. Depends on the time available and whether they have used Image prior to this lab activity.)

Set scale for the image using the difference in the recorded wavelength for the leftmost and rightmost bright line.

Use the plot profile tool to accurately determine the wavelength of each bright line in the Balmer series and record these wavelengths.

Use c=f(lambda) to calculate the frequency of each bright line.

Use E=hf to determine the energy of each bright line.

Convert these energies to electron volts and plot them on an appropriately scaled energy well diagram.

Compare their diagram to that given in the NYS Physics Reference Tables.

Explain the differences between their diagram and that given in the reference tables.

Predict in which part of the electromagnetic spectrum the radiation for the n=1 transitions would occur.

Submit a lab report in standard format using Scientific Notebook software and submit this report electronically.

CONCEPT APPLICATION:

Students will repeat the activity for an unknown element. I intend to use mercury as the unknown. Student's have an energy level diagram for mercury in their reference tables. Students will revise their lab reports in Scientific Notebook. They may correct any part(s) of the original (hydrogen) lab they feel were in error. Students will append data, results, and conclusions regarding the unknown element (mercury) and submit these reports electronically.

ACTIVITY DEBRIEFING OR SUMMARY:

Students will turn in their lab reports on hydrogen spectra. The lab reports will be reviewed and feedback from these reports will be used to structure a review of the laboratory activity and initiate a discussion regarding any student problems.

ASSESSMENT PROCEDURES:

The first lab (hydrogen) report will be graded on a pass/fail basis with the discriminating factor being whether the students completed the activity and made a good faith effort to create an energy level diagram.

The second lab (mercury) report will be graded on a 100 point scale from the standard grading criteria for laboratory reports that has been used throughout the year. Students have been given information regarding these reports and by this time, late in the school year, should be comfortable with those criteria.

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Authors or Montana State University

last updated 8/13/99