Introduction/Motivation

The Research Experience for Teachers Program http://www.cs.appstate.edu/ret

Introduction/Motivation:

Neils Bohr studied the atomic line spectra for hydrogen and investigated the relationship between the line spectra and the structure of the atom. He proposed that electrons in an atom can only have specific energy values, called energy levels, and that electrons could jump up to a higher level only when they absorbed a photon of light that exactly matched their energy value. A photon is a quantized unit of electromagnetic radiation. By exciting the electrons of an atom with energy light we cause electrons to jump to a higher energy level.

At some point the electrons will lose that excess energy and fall back to their lower, ground state, energy level. It is the emission of this excess energy, in the form of a photon, which results in the colored visible light which corresponds to bands on the atomic line spectra. Each colored line represents a transition between a particular pair of energy levels. For example, a red light might indicate a transition between energy level n=1 and n=2. A violet line may indicate a transition between energy levels n=1 and n=4. The energy of these lines can be calculated from its wavelength and thus can give us a picture of how the different energy levels are structured within the atom. Because each element is unique, its set of atomic line spectra is also unique. The wavelengths of visible light are given in units of nanometers.

In this activity you will use the Finch to act as an electron that is moving through the Bohr Model of the Hydrogen atom. This will allow you to visualize electronic transitions as well as use data collected in order to determine the wavelength of energy associated with each transition.

Materials List:

 Finch Robot

 Snap Computer software

 Meter sticks

 Computer/laptop (Snap program will not run on tablet devices)

 Small flashlight / light source

 Large paper at least 50 x 22 in.

Background: You should be familiar with electron behavior, Bohr Diagams, metric conversions, and calculaions.

Preparation: Connecting the Finch Use the USB cable provided to connect the Finch to your Computer/Chromebook/Laptop.

 Double click on “Bird Brain” Software to open it

 In the “Bird Brain” window click “Open Snap”

 In the “Snap” window, click Import File

 Import electron jump.xml file from the “associated files” folder.

Lab Activity: 1. Draw a small nucleus at the very end of the poster board 2. Draw a line 20 cm from the edge of the poster board to represent the n=1 energy level 3. Place the Finch (electron) in the n=1 energy level of your Hydrogen atom

4. Activate the program by clicking on the top of the large line of code. The code will appear to be glowing once it is activated.

5. There are several sensors on the head of the Finch. You will be utilizing the light sensor.

6. Using the flashlight, shine the light on the Finch. If the Finch moves, then he has “absorbed” energy. The Finch will move a specific distance in response to the intensity of the light.

7. When the Finch moves forward and stops, make a mark on your atom diagram where the nose stops, and write what color you observe when he “falls” back to a lower energy level. Make a mark on your atom where the Finch stopped when he “fell.” This will act as your n=2 energy level, and is where the Finch will fall to after each absorption.

8. The Finch’s colored LED will turn off as it resets to n=1 for the next transition. You may need to physically move the Finch to have his nose at n=1.

9. Continue to shine light and mark his transitions until you mark three distinct distances on your atom. 10. Measure the distance from n=1 to each spot that the inch stopped in several different angles to create accurate semi circles

11. Measure the distance between n=2 and each of three marked spots on your atom in cm. Record this value Data Table 1. In order to properly scale for the calculations section of your report you will use 1 cm = 104Hz (this is not a “real” conversion, but necessary to fit the parameters of the lab). Your measured value will be used as your frequency.

12. Continue this process until you have measured three distinct electronic transitions.

Assessment:

1. Draw in the missing energy levels on your Hydrogen atom based on your marked data, and label the energy levels n=2 etc. (The last shell is n=6 not n=5. n=5 was skipped due to its close proximity to n=6).

2. Calculate the wavelength of each photon emission and record in using the following formula: λν = c λ= wavelength (nm) ν = frequency (Hz) *your measured distance* -1 c = speed of light constant 3.00 x 10 nm 3. Create a data table to organize your results. EX: Energy Level Measured Frequency value Calculated Color Transition Distance (cm) used (Hz) Wavelength (nm) Observed n=5  n=2 69.0 69.0 x 104 4.34 x 10-7 orange

4. What did you have to do in order to move the finch to move farther from the start, and how did this relate to the amount of energy absorbed / emitted? 5. By looking at the code, determine what light intensity is required to produce red and blue light.

6. How does If I were to look at the electromagnetic spectrum what causes the light emitted to be seen as different colors?

7. Thinking about that what kind of light would be emitted then if the electron where to absorb a more intense photon?

8. In your own words describe the process of electron absorption and emission, include how different light intensities cause different photon emissions.

9. Using your reference table, determine the actual wavelengths and colors for each electron transmission. Use this information to calculate the percent error in your wavelength calculations.

10. By manipulating the code, try to demonstrate two additional electron transitions that will emit electromagnetic radiation in a form other than visible light. Call your teacher over and demonstrate / explain your new transitions.