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HNRS 227 Lecture #9 Chapter 9 Atomic Structure presented by Prof. Geller 24 September 2002 Overview of Chapter 9 Atoms and atomic structure The Bohr Model Atomic Spectra Quantum Mechanics Electron Configurations Quarks Atoms and Atomic Structure Atoms “smallest” unit of matter Nucleus protons (positively charged) neutrons (neutral) Electrons orbit nucleus negatively charged Kirchoff’s Spectral Laws Kirchoff’s Spectral Laws (empirical) Continuous Spectrum what produces them? Emission Spectrum what produces them? Absorption Spectrum what produces them? Kirchoff’s First Spectral Law Any hot body produces a continuous spectrum if it’s hot enough it looks something like this digitally like this Intensity Wavelength Kirchoff’s Second Spectral Law Any gas to which energy is applied, either as heat or a high voltage, will produce an emission line spectrum like this or digitally like this Intensity Wavelength Kirchoff’s Third Spectral Law Any gas placed between a continuous spectrum source and the observer will produce a absorption line spectrum like this or digitally like this Intensity Wavelength The Photoelectric Effect A prelude to the Bohr atom experiment explained by Einstein, but performed by others what caused this strange result? Prelude to Bohr Einstein used Planck’s quantized particles energy of photon is related to frequency of light, not intensity need high enough frequency to get electrons released from metallic surface •E = h f Bohr’s Atom - Atomic Spectra Best described the workings of the Hydrogen atom one proton and one electron “around” the proton moving in orbits that are discretized (quantized) so that no intermediate orbits are allowed Absorption Emission Quantum Mechanics and Duality of matter act as waves or particles Matter waves De Broglie l = h / m*v Electron Configurations Atomic number = number of protons = number of electrons Pauli Exclusion Principle no two electrons in an atom can have the same 4 quantum numbers energy level, sublevel, orientation, spin Heisenberg Uncertainty Principle can’t precisely measure both position and momentum Quarks Too many subatomic particles could there be smaller particles Protons and neutrons consist of quarks have partial charges • 1/3 and 2/3 Leptons - light particles like electrons Hadrons - heavy particles like protons made up of quarks