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lect12_reel2 - Electronic Excitations and Types of Pigments...

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Electronic Excitations and Electronic Excitations and Types of Pigments Types of Pigments Chemistry 123 Spring 2008 Dr. Woodward
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Electronic excitations and Absorbed Light Electronic excitations and Absorbed Light Intra-atomic excitations Intra-atomic excitations Transition metal ions, complexes and compounds (d-orbitals) Lanthanide ions, complexes and compounds (f-orbitals) Interatomic (charge transfer) excitations Interatomic (charge transfer) excitations Ligand to metal (i.e. O 2−   Cr 6+  in SrCrO 4 ) Metal-to-Metal (i.e. Fe 2+    Ti 4+  in sapphire) Molecular Orbital Excitations Molecular Orbital Excitations Conjugated organic molecules Band to Band Transitions in Semiconductors Band to Band Transitions in Semiconductors Metal sulfides, metal selenides, metal iodides, etc. When a molecule absorbs a photon of ultraviolet (UV) or visible radiation, the energy  of the photon is transferred to an electron.  The transferred energy excites the  electron to a higher energy atomic or molecular orbital. Because atoms and  molecules have quantized (discrete) energy levels light is only absorbed when the  photon’s energy corresponds to the energy difference between two orbitals.  
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Absorption of Light by Atoms Absorption of Light by Atoms When atoms absorb light the energy of a photon is transferred to an electron  exciting it to a higher energy atomic orbital.  This is illustrated above for a the  excitation of an electron from a 1s orbital to a 2s orbital in a hydrogen atom. Photon of light
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Hydrogen Line Spectrum Hydrogen Line Spectrum n =3 to n =2 n =4 to n =2 n =5 to n =2 n =6 to n =2 Recall from Chem 121 the line spectrum of a hydrogen atom (shown above). The light is produced due to emission, where the electron falls down to a lower energy level and gives of a photon of light whose energy corresponds to the energy difference between orbitals. Emission is simply the opposite of absorption. To get electrons into higher energy orbitals electrical energy is used. Neon lights work on the same principle.
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Orbital Energies in Multielectron Atoms Orbital Energies in Multielectron Atoms Energy 1 s 2 s 2 p 3 s 3 p 3 d n = 1 n = 2 n = 3 n = 0 1 s 2 p 3 d 2 s 3 p 3 s 4 p 4 s Single Electron Atom Multi-Electron Atom
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The Influence of Surrounding Atoms The Influence of Surrounding Atoms
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This note was uploaded on 06/03/2011 for the course CHM 123 taught by Professor Woodward during the Spring '08 term at Ohio State.

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lect12_reel2 - Electronic Excitations and Types of Pigments...

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