Title: Atomic Emission Spectra

Purpose:

  • to measure the emission spectra of several different gases
  • to compare the emission spectra of these different gases
  • to determine the relation (if any) among atomic number, number of valence electrons, and number of emission spectra lines.

Materials: Virtual ChemLab Environment

Procedure:

  1. Start Virtual ChemLab.
  2. Enter the General Chemistry Laboratory (Click Guest)
  3. Open the Quantum Lab by clicking on the lab table to the far right of the lab. There is a starburst ----symbol on the lab table.
  4. READ THE ENTIRE EXPERIMENT BEFORE YOU START
  5. You will need to set up the optics table for the Emission Experiment:
  6. Go to SOURCES on the top shelf in the Stockroom area to enter the Stockroom.
  7. Click on the clipboard that is on the right wall, just above the help bell.
  8. Now Click on Preset Experiment 9: Photoemission—H2.
    This will set up the lab for you!
  9. Click the green Return to Lab arrow.
  10. You will see a large open window labeled Spectrometer. Move the spectrometer window so you can see the lab table and setup:
    The spectrometer is on the right, and the sample tube holder with a tube of H2 gas with its energy source are in the center.
  11. The emission spectrum is in the detector window on the top (colored lines on a black background) and a graph of intensity vs wavelength () is on the white screen area.
  12. Click on the Visible/Full switch to magnify only the visible spectrum.
    You will see four peaks in the spectrum. If you drag your cursor over a peak, it will identify the wavelength (in nm) in the x- coordinate field in the bottom right corner of the detector window. For example, the wavelength of the 1st peak is approximately 410 nm.
  13. Record the wavelengths of the four peaks in the visible hydrogen spectrum in the Data Table. (Round to whole numbers.)
  14. To investigate the emission spectra for helium, you need to exchange gas samples, Double-click or click and drag the Electric Field and place it on the Stockroom counter in the MODIFIERS area, and double-click or click and drag the Gas (H2) sample tube and place it on the Stockroom counter in the SAMPLES area.
  15. Click in the SOURCES area to enter the Stockroom. Click on the Gases samples on the top shelf. Click on the cylinder labeled He to replace the H2 in the sample tube with helium gas.
  16. Click on the green Return to Lab arrow.
  17. Drag the gas sample tube off the stockroom counter and place it in the middle of the table as indicated by the spotlight.
  18. Drag the Electric Field and place it on top of the gas sample tube. It will align itself correctly!
  19. Carefully click the button just above the left zero on the Electric Field controller and change the voltage to 300 V. (This is a little tricky, so be patient!!)
  20. Turn on the Spectrometer by clicking on the red/green button and click the Visible/Full switch to view only the visible spectrum.
  21. Determine the wavelength (in nm) for all the lines and record in the Data Chart.
  22. Repeat for neon, sodium, mercury, nitrogen, and iodine. Determine the color and wavelength for all the lines and record in the Data Chart. (Remember to set the electric field to 300 V for each trial!)
  23. Use the periodic table to find the atomic number and number of outer electrons (valence electrons) for each element you investigated and record in the Data Table as well.
  24. Graph atomic number vs number of emission spectra lines.
  25. Graph number of outer shell electrons vs emission spectra lines.

Results:

Element / Atomic # / # Valence Electrons / # Emission Spectra Lines / Color and (nm)
H2 / 1 / 1 / 4 / violet = 410 nm
blue =
blue-green =
red =
He
Ne
Na
Hg
N2
I2

Use Create a Graph or Graph Pad to construct the graphs.

Paste the images below the Data Chart.

Discussion:

Compare and contrast the numbers and colors of the emission lines for the elements you investigated.

Conclusion: 2 statements:

Whether or not there is a relation between atomic number and number of emission spectra lines.

Whether or not there is a relation between number of valence electrons and number of emission spectra lines.

Reflection: Commentary on what you learned about emission spectra.

Save a copy of this lab writeup in your folder and in your Virtual LabNB Folder on the Shared Folder. (You may email this lab writeup to and I will save it in your Virtual LabNB)

Print out a copy of this lab and tape it into your LabNB!

Judith NuñoChemistry2006/2006