11-atomic-spectra - CHM151LL A TOMIC SPECTRA ELECTRON...

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CHM151LL: ATOMIC SPECTRA & ELECTRON ENERGY LEVELS | 1 Atomic Spectra & Electron Energy Levels OBJECTIVES: To measure the wavelength of visible light emitted by excited atoms to calculate the energy of that emitted radiation to calculate, for hydrogen, the energy levels occupied by the excited electrons before they returned to lower energy levels. DISCUSSION: We have obtained much of the information concerning the arrangement of electrons within atoms by spectroscopy , the examination of the light absorbed or emitted when atoms undergo a change of energy state. Atoms may absorb or emit energy at many frequencies, corresponding to visible light, infrared, ultraviolet, or X-rays. In this lab exercise, you will observe the visible light emitted by excited atoms. Visible light constitutes only a very narrow range of the much wider electromagnetic spectrum. This spectrum also includes radio, microwaves, infrared, ultraviolet, X-radiation, and gamma radiation. Increasing wavelength gamma X-ray ultraviolet visible infrared microwave radio violet indigo blue green yellow orange red Decreasing frequency Figure 1: The electromagnetic spectrum We describe electromagnetic radiation as an oscillating disturbance in the electric and magnetic fields, traveling through space at the speed of light, c = 2.998 × 10 8 m/s. We can specify the oscillation using either the wavelength, λ ( lambda ) or the frequency, ν ( nu ). The wavelength gives the distance between equivalent points on sequential waves (see Figure 2) and frequency gives the number of waves per second that pass a reference point. Figure 2: Wavelength and amplitude Because light travels through space at a constant speed, the wavelength and frequency are inversely proportional: !" = c (1) As one increases, the other must decrease. Reconsider Figure 1 as you think about this relationship. The energy of the light emitted by an atom is directly proportional to the light’s frequency: ! E = h ! (2) where Planck's constant, h = 6.626 × 10 –34 J · s for each emitting atom.
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2 | CHM151LL: ATOMIC SPECTRA & ELECTRON ENERGY LEVELS How does the nature of light give information about the electronic structure of the atom? The energy absorbed by an atom boosts an electron to a higher energy state. As the electron returns to lower energy states it releases the energy it absorbed as electromagnetic radiation, though not necessarily all in one step. Some of this energy may lie in the X-ray, some in the ultraviolet, and some in the visible, infrared, or
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11-atomic-spectra - CHM151LL A TOMIC SPECTRA ELECTRON...

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