Biology 2005N Paper 3 Option H

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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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