Ch 5.2 Atomic Theory

Ch 5.2 Atomic Theory - Atomic Spectrum of Hydrogen W h ite...

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Chapter 5 17 Atomic Spectrum of Hydrogen White light passed through a prism shows a continuous spectrum. Light emitted from atoms when passed through a spectrum shows only spectral lines.
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Chapter 5 18 The Person Behind the Science Niels Bohr (1885-1962 ) Highlights Worked with J.J. Thomson (1911) who discovered the electron in 1896 1913 developed a quantum model for the hydrogen atom During the Nazi occupation of Denmark in World War II, escaped England and America Associated with the Atomic Energy Project. Open Letter to the United Nations in 1950 peaceful application of atomic physics Moments in a Life Nobel Prize in Physics 1922
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Chapter 5 19 Energy Levels in the Bohr Model of the Atom The electron in a hydrogen atom moves around the nucleus only in certain allowed circular orbits. The energy levels of the electron are quantized.
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Chapter 5 20 Bohr Model of the Atom What Bohr got right: – The model gets the energy levels correct in that the experimental spectrum can be reproduced. – As the electron becomes more tightly bound its energy becomes more negative relative to a separate electron and proton. The closer the electron is to the nucleus, the more energy was released when the atom formed. What Bohr got wrong: – His model only worked for the hydrogen atom. It failed when it was used to try to predict the spectra of other atoms. – Electrons DO NOT move around the nucleus in circular orbits. E = " 2.178 # 10 " 18 J Z 2 n 2 $ % ( )
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Chapter 5 21 Calculate the wavelength that must be absorbed to excite an electron from its ground state (n=1) to the excited state with n=3.
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Chapter 5 22 Problem to do on your own • Calculate the energy to remove an electron from a hydrogen atom when the atom is initially in its ground state (hint: what is n when the electron has been removed)? This will be a very quick PRS question at the start of class on Friday.
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Chapter 5 23 Development of Quantum Mechanics • If electrons exhibit wave-like properties, then could wave mechanics be used to describe atoms and molecules? • Louis de Broglie: Wave nature of particles • Werner Heisenberg: The Uncertainty Principle • Erwin Schrödinger: The Schrödinger Equation • Many others that we don’t have time to discuss.
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24 Heisenberg Uncertainty Principle In 1927, Werner Heisenberg established that it is impossible to measure, with arbitrary precision, both the position and the momentum of an object You cannot measure/observe something without changing that which you are observing/measuring. When we take a measurement we
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Ch 5.2 Atomic Theory - Atomic Spectrum of Hydrogen W h ite...

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