Spectra - Experiment 11 Revision 1.1 Spectroscopy of Atoms...

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Experiment 11 Revision 1.1 Spectroscopy of Atoms and Molecules Learn about the Interaction of Photons with Atoms and Molecules. Learn about the Electronic Structure of Atoms. Learn about Spectroscopy. Learn about Beer’s Law. In this laboratory exercise, we will probe the behavior of electrons within atoms using Emission and Absorbance Spectroscopy. We will first examine the photons emitted from excited atoms of various salts. Then we will observe the line spectrum of excited Hydrogen atoms. Finally, we will leverage the photon absorbance of a solution of Copper Ions to determine the concentration of those Ions. Probing the behavior of electrons within atoms is problematic; atoms themselves are far too small to be seen and their presence must be inferred, and the electron itself is a quantum mechanical object. However, understanding the behavior of these electrons is important because this behavior determines an atom’s chemistry. Thus, we must find an indirect probe of the electronic behavior of an atom. It is found that useful probes of this behavior are the photons of light which interact with an atom. If an interacting photon’s energy matches that of an electronic transition within the atom, the photon can be absorbed. Conversely, an electronically excited atom can relax and emit a photon whose energy matches the atom’s electronic transition. These photons are directly observable; therefore they provide us with a window on the behavior of electrons within an atom. In the realm of molecules, the experiment is much the same; electronic transitions of the molecule will allow for either absorbance or emission of photons. And, again, the energy of these photons can be directly measured, giving us insight into the behavior of the electrons in the molecule. Photons are quantum mechanical objects that exhibit a Wave-Particle Duality. The wavelength ( λ ) of a photon is related to its speed ( c ) via: c = λ ν (Eq. 1) where ν is its frequency. In a vacuum the speed of a photon is c = 2.99792 x 10 8 m/sec. Its energy (E) is then related to its frequency via: E = h ν (Eq. 2)
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where h represents Planck’s cons of energies, from very low energ Electromagnetic Spectrum of pho Typical electronic transitions wit photons have energies in the Vis If a photon of the correct Energy required for an atomic quantum s This phenomenon will result in a radiated with White Light. Conv quantum state relaxes, a photon w emitted: stant; h = 6.62608 x 10 -34 Jsec. Photons can cov gy Radio Waves to high energy Gamma Radiatio oton wavelengths is represented below: ithin atoms and molecules are such that the corre sible and Ultraviolet regions of the spectrum.
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This note was uploaded on 11/06/2008 for the course CHEM 121 l taught by Professor Na during the Spring '08 term at John Brown Univeristy.

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Spectra - Experiment 11 Revision 1.1 Spectroscopy of Atoms...

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