Lecture2010fa

Lecture2010fa - Chemistry 83! 11/16/10 ! Technologies Based...

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Chemistry 83 11/16/10 1 Technologies Based on Interactions of Matter with Electromagnetic Radiation (EMR) Technologies that provide for the wants of humans: quality and quantity of life Tro, 162 Review of electromagnetic radiation Visible (Vis)
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Chemistry 83 11/16/10 2 Electromagnetic radiation and human wants • Electromagnetic radiation (emr) is energy moving through space in a wave motion • Emr interacts with matter (atoms and molecules) by changing their total energies compared to “room conditions”: 25 C, 1 atm pressure – During exposure to emr, matter absorbs energy – Following exposure to emr, matter emits the extra energy it absorbed to return to “room conditions” • Different forms of emr provide different amounts of energy and interact in different ways with matter • These different interactions serve as the bases for technologies that can enhance human wants (quality and quantity of life) • Ground state is energy at “room conditions” • Excited states correspond to higher energies resulting from adding (red arrow) different amounts of energy from emr to the ground state • Following exposure to emr, atoms/molecules emit the extra energy (blue arrow) and return to ground state by all possible paths Absorption of energy Emission of energy 1 2 3 4 5 Ground state Excited states Energy Level Diagram Energy Representation of interactions of emr with matter
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Chemistry 83 11/16/10 3 http://www.easymeasure.co.uk/webs/3/html/510/fg1.giF Nucleus of H atom is spinning and functions as a weak magnet. Science basis for using radiowaves in technologies Tro, 166 Radiowaves change alignment of nuclear magnets with an external magnetic Feld *Resonance frequency is the frequency of the radiowave that causes change in the orientation of the nuclear magnet. Depends on strength of external magnetic field. External magnetic field
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Chemistry 83 11/16/10 4 Resonance frequencies can be used to obtain images of systems containing H atoms Tro, 167 Example of a MRI brain scan. Image shows H atoms of water in different tissues. The large white area indicates the locations of tumors. McMurray/Fay, "Chemistry", 2nd, Prentice Hall, 1998, 935 Magnetic Resonance Imaging (MRI) is a diagnostic application of radiowaves
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Chemistry 83 11/16/10 5 http://www.lsbu.ac.uk/water/images/axes.gif Science basis for using microwaves in technologies Non-polar molecules are transparent to microwave
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This note was uploaded on 12/19/2010 for the course CHEM 83 taught by Professor Bonk,j during the Fall '08 term at Duke.

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Lecture2010fa - Chemistry 83! 11/16/10 ! Technologies Based...

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