Unit3Day4-LaBrake Monday, October 21, 2013 11:32 AM Vanden - - PDF document

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Unit3Day4-LaBrake Monday, October 21, 2013 11:32 AM Vanden Bout/LaBrake/Crawford CH301 WHY DOES A FROG FLOAT IN A MAGNETIC FIELS? MORE ON BONDING THEORIES UNIT 3 Day 4 CH302 Vanden Bout/LaBrake Fall 2013 Important Information LM22 DUE Th

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CH302 Vanden Bout/LaBrake Fall 2013

Vanden Bout/LaBrake/Crawford CH301 WHY DOES A FROG FLOAT IN A MAGNETIC FIELS? MORE ON BONDING THEORIES UNIT 3 Day 4

CH302 Vanden Bout/LaBrake Spring 2012

Important Information

LM22 DUE Th 9AM Laude LM Lecture 12 and 13

Quiz: CLICKER QUESTION 1

Is the molecule CH2Cl2 ? a) polar

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CH302 Vanden Bout/LaBrake Fall 2013

Quiz: CLICKER QUESTION 1

Is the molecule CH2Cl2 ? a) polar b) nonpolar

CH302 Vanden Bout/LaBrake Fall 2013

Quiz: CLICKER QUESTION 2

Given a tetrahedral electronic geometry, which of the following hybridizations is possible? a) sp b) sp2 c) sp3 d) sp3d

TAKE A LOOK AT THE BALLONS AGAIN……

The number of sigma and pi bonds, respectively, in the following is:

Quiz: CLICKER QUESTION 3 a) 20, 5 b) 20, 4 c) 16, 9 d) 21, 5 e) 17, 4

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CH302 Vanden Bout/LaBrake Fall 2013

The number of sigma and pi bonds, respectively, in the following is:

a) 20, 5 b) 20, 4 c) 16, 9 d) 21, 5 e) 17, 4 REVIEW LEARNING MODULE 21 VB

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CH302 Vanden Bout/LaBrake Fall 2013

What are we going to learn today?

EXPLORE MOLECULAR ORBITAL THEORY

CH302 Vanden Bout/LaBrake Fall 2013

Ethanol Diatomic Oxygen

EXPLAIN THE VB HYBRIDIZATION IN ETHANOL

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CH302 Vanden Bout/LaBrake Fall 2013

ANOTHER PHYSCIAL MODEL VB MO Valence Bond Molecular Orbital localized de-localized

IT’S ABOUT THE MOLECULE NOT THE BOND……. http://www.youtube.com/watch?v=yJs5ENtilIo

CH302 Vanden Bout/LaBrake Fall 2013

What is bond strength and bond length in H2?

How can we get that? Quantum mechanics, oribitals for the whole molecule and energies for all electrons – what distance? At every distance you calculate this and you get a radial function! For the whole molecule – not just atomic orbital!

E

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CH302 Vanden Bout/LaBrake Fall 2013

E

CH302 Vanden Bout/LaBrake Fall 2013

E

BONDING AND ANTIBONDING ORBITALS

COMPARE MO TO VB FOR H2

Very similar because the bond is the molecule If the molecule is stable, then electrons in MO are lower in energy than in AO.

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If the molecule is stable, then electrons in MO are lower in energy than in AO. Number of MO in molecule = total number of AO in atoms

CH302 Vanden Bout/LaBrake Fall 2013

Combine atomic orbitals, sometimes you get

higher and sometimes you get lower energy

Remember electrons have wave functions
Constructive and destructive interference
Two possibilities

IDEAS ABOUT MO

http://winter.group.shef.ac.uk/orbitron/MOs/H2/1s1s-sigma/index.html

What does the electron configuration for He2 look like?

HOW MANY ELECTRONS? WHERE DO THEY GO? BOND ORDER = ½(# BONDING - # ANTIBONDING)

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CH302 Vanden Bout/LaBrake Fall 2013

BOND ORDER = ½(# BONDING - # ANTIBONDING)

CH302 Vanden Bout/LaBrake Fall 2013

POLL: CLICKER QUESTION 3

What is the bond order for H2

+?

CAN YOU DRAW THE LEWIS STRUCTURE?

CH302 Vanden Bout/LaBrake Fall 2013

Here are the MO’s for N2 The highest energy electrons are in what molecular orbital?

A. σ2s
B. σ*2s
C. σ2p
D. σ*2p
E. π*2p

POLL: CLICKER QUESTION 4 IS IT DIAMAGNETIC OR PARAMAGNETIC?

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CH302 Vanden Bout/LaBrake Fall 2013

MO row 2 diatomic

http://winter.group.shef.ac.uk/orbitron/MOs/ N2/2px2px-pi/index.html

CH302 Vanden Bout/LaBrake Fall 2013

Identify all valence orbitals
Use each matching pair of valence shell atomic orbitals to

build a bonding and an antibonding MO and draw the resulting MO energy level diagram

Note the total number of electrons present in the valence

shells of the two atoms, adjust for ions

Accommodate the electrons in the MO according to the

building up principle

To determine the bond order (BO), subtract the number of

electrons in the antibonding orbitals from the number in bonding orbitals and divide the result by two. BO = ½ (N – N*)

Rules for Electron Configuration and Bond Order Calculation

MOs can combine AO on dif atoms Diagram for CN-

HOMO LUMO

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CH302 Vanden Bout/LaBrake Fall 2013

MOs can combine AO on dif atoms Diagram for CN-

HOMO LUMO Bond Order? DIAMAGNETIC OR PARAMAGNETIC?

CH302 Vanden Bout/LaBrake Fall 2013

What if its not a diatomic? Methane

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How is this tool used.. Calculate the lowest energy geometry Where is the electron density

HOMO LUMO

What if it is a complicated molecule with lots of atoms It is hard to relate the MO to AO None the less the MOs are useful

CH302 Vanden Bout/LaBrake Fall 2013

HOMO LUMO

Most molecules have

A. An even number of electrons
B. An odd number of electrons
C. Equal chance of even or odd

POLL: CLICKER QUESTION 4

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CH302 Vanden Bout/LaBrake Fall 2013

HOMO LUMO

Most molecules are

A. diamagnetic
B. paramagnetic
C. Evenly split between the two

POLL: CLICKER QUESTION 5 http://ch301.cm.utexas.edu/unit3.php

CH302 Vanden Bout/LaBrake Fall 2013

Other way we use MO, just the pi electrons

VB for sigma bonds

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CH302 Vanden Bout/LaBrake Fall 2013

MO for the pi bond Where are the electrons? Delocalized around the molecule

CH302 Vanden Bout/LaBrake Fall 2012

Typical MO for organic molecule

Almost always diamagnetic HOMO/LUMO Energy gap Light absorption

Dyes – homo lumo gap is the color that is absorbed, gaps as a function of structure Organic photovoltaics

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POLL: CLICKER QUESTION 6

Currently, plastic photovoltaics absorb in the green regions. However, chemists would like to design plastic photovoltaics that absorb in the near IR region to increase the efficiency

f the energy conversion. The chemists need to:

A) Increase the HOMO – LUMO gap B) Decrease the HOMO-LUMO gap

CH302 Vanden Bout/LaBrake Fall 2013

WHAT HAVE WE LEARNED TODAY?

The Molecular Shapes can be explained using the concept - Valence Bond Theory - Hybridized Orbitals. The bonds can be identified as sigma or pi. Bonding in molecules can be visualized using VB Bonding in molecules can be modeled mathematically using MO

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Learning Outcomes

Identify sigma and pi bonds Recognize localized vs. delocalized electrons within a structure Recognize that MO theory is a quantum mechanical method used by chemists to determine the energy of the elctrons in a molecule as well as its geometry Recognize that MO theory can be used to determine the energy of the light absorbed by a compound by exciting electrons between MOs (from HOMO to LUMO) Interpret a given MO diagram as well as fill in electrons into an MO diagram to predict bond order for a compound and predict whether it is paramagnetic or diamagnetic Recognize that constructive interference of atomic orbitals yields lower energy MO (bonding) while destructive interference lends to higher energy MO (anti-bonding)

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