Section_2.2_Orbitals_post

Section_2.2_Orbitals_post - Shapes of Molecules: CHEM 123...

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Sec. 2.2 - Orbitals 1 Shapes of Molecules: CHEM 123 Review VSEPR : Valence shell electrons pair repulsion theory Helps predict the spatial arrangement of atoms in polyatomic molecules or ions C H H H H Tetrahedral N H H H O H H Trigonal pyramidal Bent 109.5 ° 107 ° 105 ° CC H H H H B F F F Trigonal planar 120° CN H H H CO H H Be H H HH H H Linear 180° But this does not tell us anything about what is happening to the orbitals… +
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Describe the bonding and the orbitals of BeCl 2 Electronic configuration of Be is 1s 2 2s 2 Electronic configuration of Cl is 1s 2 2s 2 2p 6 3s 2 3p 5 Filled outer shell how can this bond? VSEPR : Each set of valence electrons on the central atom are arranged so that the repulsion is as small as possible: Be According to VSEPR: BeCl 2 should be linear: Cl-Be-Cl 1s 2 2s 2 2p Could promote one electron Filled outer shell how can this bond? But this would produce dissimilar orbitals with non equivalent overlap between the s orbital of Be and the p orbital of chlorine and the p of Be and p of chlorine. Experimentally it is found that the bonds are identical. For the s and p orbitals to be identical or equivalent they must have changed shape or hybridized Be Be Cl Empty p orbital can participate in one σ -bond potential energy 2 Sec. 2.2 - Orbitals
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sp hybridization 1s 2 2s 2 2p The combination of one atomic 2s orbital with one atomic 2p orbital will produce two hybridized molecular orbitals called sp hybridized orbitals Be Orbital hybridization is a mathematical combination of the 2 s and 2 p wave functions to generate wave functions for the new orbitals Empty, unhybridized p orbitals sp hybridized can form two σ bonds Be Cl Cl only one p orbital of chlorine is shown Cl Be Cl Two σ -bonding MO (p + sp) (antibonding not shown) empty p orbitals not shown potential energy 2p 2sp Full, unhybridized s orbitals Therefore, Be in BeCl 2 is sp hybridized 3 Sec. 2.2 - Orbitals
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4 H So why is there hybridization? Remember hybridization is only a model to describe what is seen in nature. Using the example of BeCl 2 : if bonding occurred with orbitals 2s (HOMO) and 2p (LUMO) the bond angle would be 90° 90° We do not observe 90° bond angles in BeCl 2 . WHY?
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This note was uploaded on 11/14/2010 for the course CHEM CHEM266 taught by Professor Forsey during the Fall '10 term at Waterloo.

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Section_2.2_Orbitals_post - Shapes of Molecules: CHEM 123...

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