UV Visable Spec PPT
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Transcript of UV Visable Spec PPT
Biology 2005N Paper 3 Option H
http://lawrencekok.blogspot.com
Prepared by Lawrence KokVideo Tutorial on UV /visible spectroscopy, transition metals complexes and splitting of 3d orbitals.
UV and Visible Spectroscopy Spectroscopy interaction of matter with radiation
Visible Spectroscopy electronic transition of valence electrons to higher energy level by absorbing radiation in visible range UV Spectroscopy electronic transition of valence electrons to higher energy level by absorbing radiation in UV range
UV and Visible Spectroscopy
Energy difference bet 2p and 3s is HIGHAbsorb UV range - ColourlessEnergy difference bet split 3d is SMALLAbsorb Visible range - ColouredPic taken from: http://www.extension.org/pages/13116/electromagnetic-spectrum
UV and Visible SpectroscopyPic taken from:http://www.hunancreative.com/24.html
Transition metal complexes are coloured due to splitting of 3d orbitals* Metal ion surrounded by ligands 1* 3d orbitals are degenerate without any ligands2
Transition metal complexes are coloured due to splitting of 3d orbitals* Metal ion surrounded by ligands 1* 3d orbitals are degenerate without any ligands2
3d orbitals split by ligands3Splitting
Explanation how splitting occurs due to electron repulsion
Explanation how splitting occurs due to electron repulsion
Splitting of 3d orbitals by ligands allow electronic transition from lower to higher stateColour formation due to splitting of 3d orbitals by ligandsTi 3+ transmit blue/violet region BUT absorb green/orange/red
Ti 3+ violet due to absorption of green/yellow region to excite electrons to higher orbital levelCu 2+ transmit blue/violet region BUT absorb green/orange/red
Cu 2+ blue due to absorption of green/yellow to excite electrons to higher level
Transition metal have different colours due to splitting of 3d orbitals presence of ligands which causes splitting partially filled 3d orbitalsCuSO4 (anhydrous) without ligands - Colourless
Why some are colourless ?Cu 2+ anhydrous colourlessCu 1+ hydrous colourlessZn 2+ hydrous colourlessSc 3+ hydrous colourlessCu 2+ hydrous - colourZn 2+ ion with ligand water - Colourless
Sc 3+ ion with ligand water - ColourlessCu 2+ ion with ligand water Colour Blue
Cu 1+ ion with ligand water - Colourless
Factors affecting colour of transition metal complexes are 1. Nature of element 2. Oxidation state 3. Type of ligands 4. Stereochemistry/shapeElements - Fe2+, Mn2+ , Cu2+ , Co2+Oxidation state ion - Fe3+ , Fe2+
Factors affecting colour of transition metal complexes are
Different ligands H20, NH3 , CI- Stereochemistry octahedral , tetrahedral
Factor 3. Different ligands different level of splitting different colourLigands CI- H2O NH3Ligands F- H2O NH3
Absorption of UV by organic molecules and chromophores
Absorption of UV radiation by C=C, C=O, N=N, N=O gpsUV Electronic transition Chromophores gpsPic taken from: http://pubs.rsc.org/en/Content/ArticleLanding/2008/NJ/b809055f
Difference bet UV and Visible absorption by
Coloured - Absorption in visible range Splitting of 3d is small falls in visible rangeTransition metals Organic molecules/chromophores Colourless - Absorption in UV range Electronic transition from bonding to antibonding orbital (involving pi or lone pair electron)
Pic taken from:http://www.lycocard.com/index.php/lyco_pub/health/Absorption of UV by organic molecules and chromophoresMore conjugation more delocalization absorption in visible range - coloured
Absorption of UV by organic molecules and chromophoresMore conjugation splitting energy less wavelength absorption increase (visible range)Summary
Absorption of UV by organic molecules and chromophores Organic molecules with extensive conjugated double bonds will be coloured Absorb in visible range
Azo dyesFood dyesSun block caroteneIndicators
Absorption of UV by organic molecules and chromophoresHow Phenolphthalein indicator changes colour ?Acidic ColourlessAlkalinePinkReason for change of colour change in conjugation change in delocalization
Acknowledgements
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Prepared by Lawrence Kok
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