CHE_106_Lecture14_2009

CHE_106_Lecture14_2009 - Chemistry 106 Lecture 14 Topic:...

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Chemistry 106 Lecture 14 Topic: Quantum Mechanics Chapter 6.3-6.6
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Flame Tests of Group 1A Elements Flames of Sodium. Flames of Lithium.
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Emission (Line) Spectra of Some Elements
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Prior to the work of Niels Bohr (1922 Nobel Prize in Physics) , the stability of the atom could not be explained using the then-current theories. – In 1913, using the work of Einstein and Planck, The Bohr Theory of the Hydrogen Atom he applied a new theory to the simplest atom, hydrogen . – Before looking at Bohr’s theory, we must first examine the “line spectra” of atoms.
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When a heated metal filament (light bulb) emits light, we can use a prism to spread out the light to give a continuous spectrum -that , spectrum containing light of Atomic Line Spectra is, a spectrum containing light of all wavelengths. The light emitted by a heated gas , such as hydrogen, results in a line spectrum - a spectrum showing only specific wavelengths of light. Neon
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For atoms and molecules one does NOT observe a continuous spectrum, as one gets from a Atomic Line Spectra Dispersion of white light by a prism white light source. Only a line spectrum of discrete wavelengths is observed. Dispersion of atomic emission light by a prism
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Emission (Line) Spectra of Some Elements
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Dispersion of Light By a Prism Flames of Lithium
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In 1885, J. J. Balmer showed that the wavelengths, λ, in the visible spectrum of hydrogen could be reproduced by a simple formula. ) ( m 10 1.097 1 1 1 7 1 - × = - The Bohr Theory of the Hydrogen Atom – The known wavelengths of the four visible lines for hydrogen correspond to values of : n = 3, n = 4, n = 5, and n = 6. 2 2 n 2 λ
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Bohr’s Postulates Bohr set down postulates to account for (1) the stability of the hydrogen atom and (2) the line spectrum of the atom. . nergy vel ostulate n electron can have only The Bohr Theory of the Hydrogen Atom 1. Energy level postulate : An electron can have only specific energy levels in an atom (quantized). 2. Transitions between energy levels : An electron in an atom can change energy levels by undergoing a “transition ” from one energy level to another.
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Bohr’s Postulates Bohr derived the following formula for the energy levels of the electron in the hydrogen atom. The Bohr Theory of the Hydrogen Atom – n is the principal quantum number. – R h is the Rydberg constant (expressed in energy units) with a value of 2.18 x 10 -18 J. atom) H (for ..... 3 2, 1, n n R E 2 h = - =
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Energy-level diagram for the electron in the ydrogen atom) H (for ..... 3 2, 1, n n R E 2 h = - = hydrogen atom.
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Bohr’s Postulates When an electron undergoes a transition from a higher energy level to a lower one, the energy is emitted as a photon. The Bohr Theory of the Hydrogen Atom
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CHE_106_Lecture14_2009 - Chemistry 106 Lecture 14 Topic:...

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