2.Fluorescent light and incandescent light. Point your spectroscope at a fluorescent tube in the laboratory. Can you describe what you see? How does it compare to daylight? Are there brighter and darker areas? List approximately where the bright bands occur, giving band center values in nanometers and wavenumber units. How does this spectrum compare with that produced by a conventional incandescent (glowing filament) light bulb? 3.Mercury: Fluorescent light tubes contain mercury and argon vapors, but also have a phosphorcoating painted on the inside of the tube. The light you see consists of part of the mercury spectrum, together with an approximately continuous spectrum from the phosphors. (Search on the internet for more information on how fluorescent light tubes work.) On the other hand, a blacklightis a UV light source in which all visible light from a mercury discharge tube has been filtered out, leaving only the UV part (and some infrared). You will not be able to see the spectrum of the blacklight using the naked-eye spectroscope because your eyes are not able to detect these wavelengths (and it would be harmful to attempt to do so), but your instructor will demonstrate the collection of spectra from the mercury tube and the blacklight. Note down the wavelengths of the strongest lines, including those in the ultraviolet. Color Wavelength (nm) Red Orange Yellow Green Blue Indigo Violet
CHE151Lab7_AtomicSpectra.doc Dr . Roderick M. Macrae CHE 151 B. Quantitative Exercise: The Hydrogen Atom Johannes Balmer, a Swiss schoolteacher, observed the splitting of hydrogen light from a discharge tube by a prism in 1885, and managed to calculate a formula for the positions of the lines in terms of their wavelengths. This was later rewritten by Johannes Rydberg in wavenumber units, expressing the fact that the lines corresponded to energy changes in the H atom. His formula was written where ν~is the position of the line expressed in wavenumbers (cm-1) and n = 3, 4, etc. (i) Input your values of n (x data) and the wavelengths of the lines you observe for H in nanometer units (y data) into LoggerProthen use New Calculated Column(under the Datamenu) to convert them into wavenumber units. (ii) Given that the “red” line corresponds to n=3, and the others to n=4, 5, etc., try to find a value for R, the Rydberg constant. Generate a new calculated column corresponding to 2141n−. Now select this new column as your x-axis, ν~as your y-axis, and choose a linear (or proportional) graph. Hydrogen data: n 0.25 – 1/n2λeyeν~eyeλspectrometerν~spectrometer3 4 5 6 7 8 9 Later it became possible to observe parts of the hydrogen atom spectrum outside the visible range. In addition to more lines in the Balmer series(what we have been looking at), a set of lines was discovered in the ultraviolet (the Lyman series) as well as multiple series in the infrared (Paschen, Brackett, Pfund,…). Replacing “2” in the above formula by 1, 3, etc., yielded the wavenumber values corresponding to these series. These observations were what led Niels Bohr to develop his model of the energy levels of the H atom. (See Figure
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