Ch400Ch5LN1 - Chem 400 Ch 5 Lecture Notes Part 1 Atomic...

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Chem 400 Ch 5 Lecture Notes Part 1 Atomic Structure and Modern Quantum Theory To put the timing into perspective, here is the overall timeline for some important discoveries regarding the atom and atomic structure: • Balmer’s formula for the hydrogen line spectrum in 1885 • Photoelectric effect discovered in 1887 • X-rays discovered in 1895 • Radioactivity discovered in 1896 • Electron discovered in 1897 • Planck’s quantum hypothesis applied to blackbody radiation in 1900 (beginning of quantum theory) • Einstein explains photoelectric effect using quantum hypothesis in 1905 • Plum-pudding model of atom in 1907 • Rutherford’s a-scattering experiment in 1909 • Rutherford’s model of atom in 1911 • Bohr’s model of atom in 1913 • deBroglie’s hypothesis on the wave nature of matter in 1924 • Heisenberg’s Uncertainty Principle in 1925 • Schrödinger’s Wave Equation in 1926 (Quantum Mechanics is fully accepted and successfully explains atomic phenomena) Primer for the Electromagnetic Spectrum • As atoms are too tiny to see directly, most of our ideas and theories of the atom are based on experiments where we analyze light which is absorbed or emitted by atoms. • So we need to go over the basics of the electromagnetic spectrum, the light spectrum, or electromagnetic radiation. • Until recently, light has been considered to be a wave, so what are the characteristics of a wave? • Speed of light, c: • Wavelength, λ :
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• Frequency, ν : • Amplitude: • Energy, E: • Electromagnetic Spectrum: the spectrum ranges from the longest wavelength (lowest frequency and lowest energy) for the radio waves to the shortest wavelength (highest frequency and highest energy) for the gamma rays. • The visible light spectrum, the portion we see, is a tiny portion from about 380 nm (violet) to 780 nm (red). To remember the color sequence, know ROY G BIV (red, orange, yellow, green, blue, indigo, violet, where red is the lowest energy and violet is the highest energy). The Beginning of Quantum Mechanics • Classical mechanics and electromagnetic theory stipulated that light was a wave. • Several experiments had puzzling results, contradicting classical theory. • Blackbody radiation did not follow classical theory. The spectral distribution of radiation inside a blackbody (a hollow object with a pinhole for incoming radiation) was not what the classical theory predicted. Classical theory was acceptable for long wavelengths, but failed for short wavelengths (this was called the ultraviolet catastrophe). • Max Planck solved this by setting the energy of an oscillating body in the blackbody (an atom) inversely proportional to the wavelength of the incoming light radiation. Since the wavelength is inversely proportional to the frequency, Planck formulated an equation as follows: E = h ν , where h is Planck’s
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This note was uploaded on 06/25/2008 for the course CHEM 400-401 taught by Professor Dr.samples during the Fall '06 term at American River.

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Ch400Ch5LN1 - Chem 400 Ch 5 Lecture Notes Part 1 Atomic...

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