Lab spectra

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Atomic Spectra
Light, Energy, and Electron Structure

Introduction:
Sunlight passing through a prism produces a rainbow of colors – the visible spectrum. The separation of white light into its component colors occurs when light waves of different wavelengths are bent by different amounts. When a pure atomic gas such as hydrogen or helium is subjected to a high-voltage electrical discharge,light is produced and the gas glows. When this light is passed through a diffraction grating, however, the spectrum it produces is different. Instead of giving the familiar rainbow of colors, the light emitted by the gas gives a series of bright, colored lines. The series of bright lines is called an atomic emission spectrum and is unique to each element.

Concepts:
Atomic emission spectrumElectron energy levels
Quantization of energy Electron transitions

Background:
Hmmm… You’re on your own for this one. Use your textbook and/or internet resources to develop a background section in your lab.
Include the following information in your background:
• Definitions of each of the concepts listed above.
• Scientists and the major contributions they made to these concepts.• Terms such as “ground state”, “excited state”, “electromagnetic radiation”, and “photon”.
• Niels Bohr’s formula for the relationship between the energy of light and its wavelength.
• What aspect of Bohr’s original model of electron structure is still included in the currently accepted theory of electron structure?
• What aspect of Bohr’s original model of electron structure is no longerconsidered valid in the currently accepted theory of electron structure?

Materials:
Colored pencils
Diffraction grating or spectroscope
Gas discharge tubes (TBA)
Power supply

Procedure:

1. Using the spectroscope or a diffraction grating, observe the continuous “rainbow” spectrum from an incandescent light bulb.

2. Observe the colors of light in the visible spectrum and thewavelength range for each color band. Sketch the spectrum of white light using colored pencils in the appropriate wavelength boxes in the Spectrum Table. Note that the units of wavelength on the spectroscope are nanometers (1 nm = 10-9 m)
3. (Optional) For optimum viewing of the emission spectra of gas discharge tubes, stabilize the spectroscope on a ring stand. Set up a ring stand in front ofthe power supply and attach one ring clamp. Place the spectroscope on the ring clamp and adjust the height of the ring clamp so that the eyepiece on the spectroscope is approximately level with the middle of the gas discharge tube. Attach a second ring clamp on top of the spectroscope so that it will be held firmly in position without moving.

4. With the power OFF, ask the instructor to insertthe hydrogen spectrum tube between the contacts on the power supply.

5. Move the power supply so that the spectrum tube is about 3-5 cm away from the spectroscope.

6. Turn on the power on the power supply and observe the atomic emission spectrum of hydrogen. Work with a partner to note the principal features in the hydrogen spectrum.

7. Turn OFF the power supply. Record the followinginformation in the Data Table for the emission spectrum of hydrogen: the number of lines, their colors, and their approximate wavelengths.

8. Using colored pencils, sketch the atomic spectrum of hydrogen in the wavelength boxes in the Data Table. Turn the power supply on and off, as necessary, to complete the observations in steps 7 and 8.

9. Check to make sure the power supply is off, then,ask the instructor to remove the hydrogen spectrum tube and insert a mercury spectrum tube.

10. Observe and note the atomic emission spectrum of mercury.

11. Turn OFF the power supply. Record the following information in the Data Table for the emission spectrum of mercury: the number of lines, their colors, and their approximate wavelengths.

12. Using colored pencils, sketch the...
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