Atomic-Spectra_pre-lab_01-09-10 - Atomic Spectra Pre-lab...

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Atomic Spectra Pre-lab Read the following material and answer the questions at the end. Submit the answers in the submission box for Atomic Spectra Pre-lab on Blackboard. When looking at light from the Sun we are looking at a combination of actual “wavelengths” or “spectra” of distinct light colors produced through atomic emission of photons by energetic electrons. In fluorescent light fixtures electrons in gas molecules in the tube are excited when electricity heats the gas. Depending on the atom it is part of, each electron can absorb energy only in certain specific amounts. When an electron absorbs the proper amount of energy it can move to a “higher shell”, a more energetic level in the atom. After a short time the electron “decays”, giving up the absorbed energy in the form of a photon and falling back to its original energy level. (See Figure 1.). Figure 1: The Atomic Absorption and Emission Process 1 The energy the electron gives off produces an emission line. When many electrons in many atoms decay they produce enough photons for us to see as visible light. This will go on continuously while energy is provided to the gas source tubes used in this lab or in a fluorescent lighting fixture. Notice in Figure 2 that the elements Hydrogen and Carbon both have emission lines in the red part of the spectrum and in the blue part of the spectrum, but that they are in 1
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slightly different places and have different brightness or intensity. Carbon also has lines in the yellow and green area of the spectrum that are missing for hydrogen. Hydrogen Carbon Figure 2: Bright lines in the image above are emission lines for hydrogen and carbon in the visible part of the spectrum. 2 Electrons can also move to higher energy levels by absorbing photons. An electron absorbs a photon of the wavelength it needs to get to a higher energy level. This removes photons with that particular amount of energy from the incoming beam of light. This process is atomic absorption. The electron reemits the energy as a photon of the same wavelength as the one it
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Atomic-Spectra_pre-lab_01-09-10 - Atomic Spectra Pre-lab...

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