Chapter 7 & 9

Chapter 7 & 9 - Chapter 7/9 Lecture 18 Covalent...

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Chapter 7/9 Covalent Bonds / Gases Lecture 18 (CHEM 1010) Agenda: In class Quiz Midterm information Final Exam information Revisiting Atomic Orbital Theory Practicing Molecular Orbital Theory Chapter 9 - Gases
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Midterm information Date: March 24th / 2011 Time: 9:30am to 11:00 am Location is J127 Material: Chapter 4 (REDOX) to Chapter 7 Review is Tuesday March 22nd Review questions will be posted Friday or Saturday
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Final exam information Date: April 26th / 2011 Time: 12:00pm to 3:00 pm Location is being moved to GYM from UB2080 I wanted to have two exams in the same place rather than in two different places. You are writing with 1020 students. More information will be given later in class.
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Valence Bond Theory Valence Bond Theory : A quantum mechanical model which shows how electron pairs are shared in a covalent bond. sigma ( σ ) bonds
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Atomic orbital revisited Consider the atomic orbitals of PH3 P has electron configuration of [Ne] 3 s 2 3 p 3 There are three p orbitals that can be involved in bonding with the 1 s orbital of H 1 p orbital can easily overlap with 1 s orbital
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But what if the number of atomic orbitals does not match for bonding? Consider the atomic orbitals of CH4 C has electron configuration of [He] 2 s 2 2 p 2 There are two p orbitals that are available for bonding to make 4 bonds
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But what if the number of atomic orbitals does not match for bonding? 2 atomic orbitals CAN NOT make 4 H bonds Need to make 4 “hybrid” atomic orbitals out 2 half- occupied atomic orbitals that are p based, 1 s orbital that is fully occupied and 1 p orbital that is not occupied
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Looking at making 4 equal hybrid orbitals From VSEPR theory we know that if there are 4 bonds around a central atom and there are no lone pairs (only 4 charge clouds) then the angles must be 109.5° and the shape is tetrahedral We can algebraically combine wave equations of the “2 s” and the three “2 p orbitals of the Carbon atom to produce four identical orbitals Energy levels are between the 2 s and 2 p orbitals respectively
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Hybridization and math This mathematical process of replacing pure atomic orbitals with reformulated atomic orbitals for bonded atoms is called HYBRIDIZATION and new orbitals are called hybrid orbitals sp 3 hybrid orbitals are 25% s character and 75% p character The number of hybrid orbitals equals the total number of atomic orbitals that are combined
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What is hybridization? Hybridization is not an actual physical phenomenon The objective of hybridization is an “after-the-fact” rationalization of the experimentally observed shape of a molecule We can not see any electron charge distributions changing from those pure orbitals to those hybrid orbitals
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What about H2O and NH3 VSEPR describes a tetrahedral electron group geometry for 4 electron groups sp 3 hybridization for H2O and NH3 where some of the charge clouds are lone pairs Anticipated angles between H-O-H is 109.5° measured is 104.5° for H2O and 107° for NH3
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This note was uploaded on 10/25/2011 for the course CHEM 1010 taught by Professor Olga during the Spring '11 term at UOIT.

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Chapter 7 & 9 - Chapter 7/9 Lecture 18 Covalent...

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