CH 301 Chapter 3 notes part3

CH 301 Chapter 3 notes part3 - Chapter 3 part 1 Molecules...

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Chapter 3 part 1 Molecules with more than 1 central atom (cont) “Don’t Forget” List DRAW THE CORRECT LEWIS DOT STRUCTURE COUNT THE RHED FOR EACH CENTRAL ATOM - DETERMINE HYBRIDIZATION. NOTE: A DOUBLE BOND WILL NEED ONE HALF FULL P ORBITAL FOR THE TWO ATOMS PARTICIPATING IN THAT BOND. NOTE: A TRIPLE BOND WILL NEED TWO HALF FULL P ORBITALS FOR THE TWO ATOMS PARTICIPATING IN THAT BOND. REMEMBER WHERE LONE PAIRS WILL BE PLACED FOR EACH OF THE ELECTRONIC GEOMETRIES Try CO 2 for yourself: Linear molecule, two lone pairs on each O atom. In order for C to form a pi bond to each of the O’s it must keep TWO of the 2p orbitals unhybridized and each much have 1 electron, ready to overlap with a half full 2p orbital from O. But it also needs to have two orbitals pointing 180º apart to sigma bond to these O atoms, so we must use the 2s and one of the 2p orbitals to make two sp orbitals. The lone pairs on the O are accomodated so: one in the 2s and one in one of the 2p orbitals. The other two 2p orbitals of the Os are half full, one from each overlaps with a sp orbital from the C (sigma bond) and the other overlaps with a 2p orbital from the C (pi bond). Overall, we have a non polar molecule with polar bonds. Benzene, C 6 H 6 - a cyclic molecule C C C C C C H H H H H H C C C C C C H H H H H H TWO resonance structures. The true structure is between. Apply VB theory: To make 120º angles the C atoms are sp 2 hybridized. This leaves one electron in a 2p orbital to pi bond by side on overlap to an electron in an adjoining C atoms’s 2p orbital: C C C C C C H H H H H H [He] sp 2 C H 1s 2p π bond σ bond Here’s the sigma structure: Green – sp 2 orbitals of C Blue - 1s orbitals of H
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Here is the PI bond frame work for benzene: Orange - p orbitals of C C C C C C C H H H H H H C C C C C C H H H H H H C C C C C C H H H H H H We consider the actual PI structure to be: Orange - π orbitals of C merged into two rings! Examples:
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This note was uploaded on 09/02/2009 for the course CHE 301 taught by Professor Fatimafakhreddine during the Spring '08 term at University of Texas at Austin.

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CH 301 Chapter 3 notes part3 - Chapter 3 part 1 Molecules...

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