20071003 Day Lecture 12

20071003 Day Lecture 12 - Todays Plan Welcome to CHM...

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1 Welcome to CHM 1220/1225 Please turn off cell phones pages iPods Thank you! Today’s Plan Announcements Complete Chapter 10 • Pre-lecture Assignment 12 will be available at 2:00 p.m. today and is due by noon, Friday, October 5, 2007. • Chapter 10 Quiz is due by noon, Friday, October 5, 2007. • Chapter 10 Homework is due by 12:50 p.m. Friday, October 5, 2007 Chapter 10 Molecular Geometry and Chemical Bonding Theory Molecular Geometry and Chemical Bonding Theory Molecular Geometry and Directional Bonding 1. The Valence-Shell Electron-Pair Repulsion (VSEPR) Model 2. Dipole Moment and Molecular Geometry 3. Valence Bond Theory 4. Description of Multiple Bonding Molecular Orbital Theory 5. Principles of Molecular Orbital Theory 6. Electron Configurations of Diatomic Molecules of the Second Period 7. Molecular Orbitals and Delocalized Bonding
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2 Valence bond theory is an approximate theory to explain the electron pair or covalent bond by quantum mechanics. A bond forms when An orbital on one atom comes to occupy a portion of the same region of space as an orbital on the other atom. The two orbitals are said to overlap. The total number of electrons in both orbitals is no more than two. The greater the orbital overlap, the stronger the bond. The greater the orbital overlap, the stronger the bond. Orbitals (except s -orbitals) bond in the direction in which they protrude or point, to obtain maximum overlap. Hybrid orbitals are orbitals used to describe the bonding that are obtained by taking combinations of atomic orbital of the isolated atoms. The number of hybrid orbitals formed always equals the number of atomic orbitals used. Hybrid orbitals are named by using the atomic orbitals that combined: one s -orbital + one p -orbital give two sp -orbitals one s -orbital + two p -orbital give three sp 2 -orbitals one s -orbital + three p -orbital give four sp 3 -orbitals one s -orbital + three p -orbital + one d -orbital give five sp 3 d -orbitals one s -orbital + three p -orbital + two d -orbital give six sp 3 d 2 -orbitals Hybrid orbitals have definite directional characteristics as described in the table below.
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3 To obtain the bonding description about any atom in a molecule: Write the Lewis electron-dot formula. Use VSEPR to determine the electron arrangement about the atom. From the arrangement, deduce the hybrid orbitals. Assign the valence electrons to the hybrid orbitals one at a time, pairing only when necessary.
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This note was uploaded on 02/02/2010 for the course CHM 1220 taught by Professor Barber during the Spring '07 term at Wayne State University.

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20071003 Day Lecture 12 - Todays Plan Welcome to CHM...

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