Lecture 2 Notes 53760 - Lecture 2 Notes B. A. Rowland 53760...

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Lecture 2 Notes B. A. Rowland 53760 Atomic Spectra Each atom’s spectrum is a unique identifier—no other atom will emit exactly the same frequencies as other elements on the periodic table. In this way atomic spectra are like human fingerprints—each one is distinct and can be used for identification purposes. For example, we can analyze which elements are contained in our Sun without ever sending a manned mission there to collect a sample because we can analyze the light received from the Sun for the specific fingerprint of whichever element we are interested in. Just as in hydrogen, each line in an atomic spectrum represents an electronic transition between two energy levels in that atom. A goal for quantum mechanics would be to be able to compute these spectra for each element (something Bohr could not do). In fact these different spectral signatures in the elements can be used in spectacular fireworks displays, with sodium giving yellow (also seen in highway lights), barium giving green, strontium giving red (also used in highway flares), magnesium giving white (also used in sparklers) and copper giving blue. Practice problem: With an absorbance spectrum, the electrons in the atom are undergoing transitions to _______ (higher, lower) energy states than they started with. However, with an emission spectrum the electrons are coming from a ________ (higher, lower) energy level to a _______ one. Rydberg's Equation : Please see Lecture 1 Notes section 'Spectra'. Practice problem: Compute the wavelengths (in nm) of the first 4 Lyman lines. Bohr's Hydrogen : Also see section 'Niels Bohr' under 'Atomic Models' in Lecture 1 Notes. Bohr realized that the lines in the hydrogen emission spectrum were due to electronic transitions in a quantum atom. Because of the wave-particle duality of the electron, there is a de Broglie wavelength for each electron. Bohr reasoned that the electron could occupy circular areas around the nucleus for which he could fit a whole-number multiple of wave crests (there can be no half waves or quarter waves as that would entail wave
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Lecture 2 Notes 53760 - Lecture 2 Notes B. A. Rowland 53760...

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