IB Chemistry Resonance, Delocalization of Ozone and Benzene

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IB Chemistry Resonance, Delocalization of Ozone and Benzene

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  • 1. Tutorial on Resonance, Delocalization andcatalytic destruction of Ozone.Prepared byLawrence Kokhttp://lawrencekok.blogspot.com

2. Delocalization of electronsResonance Describing delocalization of electrons within a molecule/polyatomic ionwhere bonding cannot be express by ONE single Lewis structureDelocalization of bond electrons spread over more than 2 nuclei electrons are shared electrons spread more stableResonance structures ozoneOzone 3 Oresonance structure 1 resonance structure 2resonance hybridUV radiationOzone at stratospherestrongest radiation 3. Delocalization of electronsResonance Describing delocalization of electrons within a molecule/polyatomic ionwhere bonding cannot be express by ONE single Lewis structureDelocalization of bond electrons spread over more than 2 nuclei electrons are shared electrons spread more stableResonance structures ozoneresonance structure 1 resonance structure 2resonance hybrid All bonds O-O are identical in length and strength Hybrid of 2 resonance structures NO O-O (single) or O=O (double) bonds found Only O ----- O bond Intermediate in character bet single and double bond1 1 Bond Order = 2Ozone 3 OClick here on video ozoneUV radiation Pale blue gas, polar, dimagnetic Oxidizing agent Potent respiratory hazard and pollutant at ground level Beneficial prevent UV B/C from reaching Earth surface Highest ozone level in stratosphere (10 km and 50 km)Ozone at stratospherestrongest radiation3 O 4. FORMAL CHARGE (FC)Formal ChargeTool/Model for comparing which Lewis structures is more acceptableTreats covalent bond with equal electron distribution no electronegativity differences bet atomElectronegative atom has negative while least electronegative atom has positive formal chargeFormula formal chargeV - valence electrons of atomL lone pair electronB bonding electron molecule Formal charge sulfur dioxideformal charge for OL +formal charge for O formal charge for OL + L + L + 5. FORMAL CHARGE (FC)Formal ChargeTool/Model for comparing which Lewis structures is more acceptableTreats covalent bond with equal electron distribution no electronegativity differences bet atomElectronegative atom has negative while least electronegative atom has positive formal chargeFormula formal chargeV - valence electrons of atomL lone pair electronB bonding electron molecule Formal charge sulfur dioxideformal charge for OV- Valence electron O = 6L- Lone pair electron O = 4B- Bonding electron O = 4L +FC = 6 (4 +2) = 0formal charge for OV- Valence electron O = 6L- Lone pair electron O = 6B- Bonding electron O = 2FC = 6 (6+1) = -1formal charge for OV- Valence electron O = 6L - Lone pair electron O = 2B - Bonding electron O = 6FC = 6 (2+3) = +1All resonance structure contribute to electronic structure.Real structure is combination of them.+1Lowest formal charge (stable), contribute more than less stable structure.0 -1Sum of formal charges must be zero for neutral or equal to charge on ion. L + L + L + 6. Ozone Good and BadGood Side Bad SideOzone in Strastophere blocks UV B + C Ozone in Troposphere act as Greenhouse gasOzone in ground level act asPollutantPhotochemical 7. Ozone Good and BadGood Side Bad SideOzone in Strastophere blocks UV B + C Ozone in Troposphere act as Greenhouse gasOzone in ground level act asPollutantPhotochemicalClick here on ozone depletionsubstances ODS (phaseout)Why ozone able to absorb UV B and UV C?Breakdown of ozone High UV radiation Skin cancer- DNA mutationOzone depletionUV ExposureOzone Hole 8. Ozone absorb UV radiationOzone absorb UV B/CO=ODoublebondO=O=OIntermediateBond length/pm 121 127Bond enthalpy/kJmol-1498 364Bond order 2 1.5Dissociation by UV