Lect19 - Lecture 19 Building Atoms and Molecules e r n=3...

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Lecture 19, p 1 Lecture 19: Building Atoms and Molecules + e r + e ψ even + e r n = 3 n = 2 n = 1
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Lecture 19, p 2 Today Atomic Configurations States in atoms with many electrons – filled according to the Pauli exclusion principle Molecular Wave Functions: origins of covalent bonds Example: H + H H 2
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Nuclear Magnetic Resonance Nuclear Magnetic Resonance Just like electrons, the proton in the H atom also has a spin, which is described by an additional quantum number, m p , and therefore also a magnetic moment. However, it is several orders of magnitude smaller than that of the electron. c The energy difference between the two proton spin states in a magnetic field is 660 times smaller than for electron spin states! c But… There are many more unpaired proton spins than unpaired electron spins in ordinary matter. Our bodies have many unpaired protons in H 2 O. Detect them …. .. In order to image tissue of various types, Magnetic Resonance Imaging detects the small difference in the numbers of “up” and “down” hydrogen proton spins generated when the object studied is placed in a magnetic field. Nobel Prize (2003): Lauterbur (UIUC) www.beckman.uiuc.edu/research/mri.html
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Lecture 19, p 5 Example: Nuclear Spin and MRI 1 ) The person to be scanned by an MRI machine is placed in a strong (1 Tesla) magnetic field. What is the energy difference between spin-up and spin-down proton states in this field? 2 ) What photon frequency , f, will be absorbed? Magnetic resonance imaging (MRI) depends on the absorption of electromagnetic radiation by the nuclear spin of the hydrogen atoms in our bodies. The nucleus is a proton with spin ½, so in a magnetic field B there are two energy states. The proton’s magnetic moment is μ p = 1.41 x 10 -26 J /Tesla . E B B=0 B 0
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Lecture 19, p 6 Act 1 We just saw that radio frequency photons can cause a nuclear spin to flip. What is the angular momentum of each photon? a. 0 b. ħ /2 c. ħ
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Lecture 19, p 7 Pauli Exclusion Principle Let’s start building more complicated atoms to study th e Periodic Table.
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This note was uploaded on 01/19/2012 for the course PHYS 214 taught by Professor Staff during the Fall '08 term at University of Illinois, Urbana Champaign.

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Lect19 - Lecture 19 Building Atoms and Molecules e r n=3...

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