IB Chemistry UV/visible spectroscopy, transition metal complexes and splitting of 3d orbitals
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Transcript of IB Chemistry UV/visible spectroscopy, transition metal complexes and splitting of 3d orbitals
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http://lawrencekok.blogspot.com
Prepared by Lawrence Kok
Video Tutorial on UV /visible spectroscopy, transition metals complexes and splitting of 3d orbitals.
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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
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UV and Visible Spectroscopy
Energy difference bet 2p and 3s is HIGHAbsorb UV range - Colourless
Energy difference bet split 3d is SMALLAbsorb Visible range - Coloured
Pic taken from: http://www.extension.org/pages/13116/electromagnetic-spectrum
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UV and Visible Spectroscopy
Pic taken from:http://www.hunancreative.com/24.html
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Transition metal complexes are coloured – due to splitting of 3d orbitals
* Metal ion surrounded by ligands
1
* 3d orbitals are degenerate without any ligands
2
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Transition metal complexes are coloured – due to splitting of 3d orbitals
* Metal ion surrounded by ligands
1
* 3d orbitals are degenerate without any ligands
2
3d orbitals split by ligands
3Splitting
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Explanation how splitting occurs due to electron repulsion
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Explanation how splitting occurs due to electron repulsion
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Splitting of 3d orbitals by ligands – allow electronic transition from lower to higher state
Colour formation due to splitting of 3d orbitals by ligands
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Ti 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 level
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Cu 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
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Transition metal have different colours due to• splitting of 3d orbitals• presence of ligands which causes splitting• partially filled 3d orbitals
CuSO4 (anhydrous) without ligands - Colourless
Why some are colourless ?
Cu 2+ anhydrous – colourlessCu 1+ hydrous – colourlessZn 2+ hydrous – colourlessSc 3+ hydrous – colourlessCu 2+ hydrous - colour
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Zn 2+ ion with ligand water - Colourless
Sc 3+ ion with ligand water - Colourless
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Cu 2+ ion with ligand water – Colour Blue
Cu 1+ ion with ligand water - Colourless
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Factors affecting colour of transition metal complexes are• 1. Nature of element• 2. Oxidation state• 3. Type of ligands• 4. Stereochemistry/shape
Elements - Fe2+, Mn2+ , Cu2+ , Co2+
Oxidation state ion - Fe3+ , Fe2+
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Factors affecting colour of transition metal complexes are
Different ligands – H20, NH3 , CI-
Stereochemistry – octahedral , tetrahedral
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Factor 3. Different ligands – different level of splitting – different colour
Ligands CI- H2O NH3
Ligands F- H2O NH3
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Absorption of UV by organic molecules and chromophores
Absorption of UV radiation by C=C, C=O, N=N, N=O gps
UV Electronic transition Chromophores gps
Pic taken from: http://pubs.rsc.org/en/Content/ArticleLanding/2008/NJ/b809055f
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Difference bet UV and Visible absorption by
• Coloured - Absorption in visible range• Splitting of 3d is small – falls in visible range
Transition metals Organic molecules/chromophores
• Colourless - Absorption in UV range• Electronic transition from bonding to antibonding orbital (involving pi or lone pair electron)
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Pic taken from:http://www.lycocard.com/index.php/lyco_pub/health/
Absorption of UV by organic molecules and chromophores
More conjugation – more delocalization – absorption in visible range - coloured
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Absorption of UV by organic molecules and chromophores
More conjugation – splitting energy less – wavelength absorption increase (visible range)
Summary
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Absorption of UV by organic molecules and chromophores
• Organic molecules with extensive conjugated double bonds will be coloured• Absorb in visible range
Azo dyesFood dyes
Sun block
ß carotene
Indicators
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Absorption of UV by organic molecules and chromophores
How Phenolphthalein indicator changes colour ?
Acidic Colourless
AlkalinePink
Reason for change of colour• change in conjugation• change in delocalization
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Acknowledgements
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Thanks to source of pictures and video used in this presentation
Thanks to Creative Commons for excellent contribution on licenseshttp://creativecommons.org/licenses/
Prepared by Lawrence Kok
Check out more video tutorials from my site and hope you enjoy this tutorialhttp://lawrencekok.blogspot.com