MAGNETIC FIELD? MORE ON BONDING THEORIES UNIT 3 Day 5 What are we - PowerPoint PPT Presentation

Sparks CH301 WHY DOES A FROG FLOAT IN A MAGNETIC FIELD? MORE ON BONDING THEORIES UNIT 3 Day 5

What are we going to learn today? EXPLORE MOLECULAR ORBITAL THEORY

Quiz: CLICKER QUESTION Given a tetrahedral electronic geometry, which of the following hybridizations is possible? a) sp b) sp 2 c) sp 3 d) sp 3 d

EXPLAIN THE VB HYBRIDIZATION IN ETHANOL Ethanol Diatomic Oxygen

http://www.youtube.com/watch?v=yJs5ENtilIo ANOTHER PHYSCIAL MODEL VB MO Valence Bond Molecular Orbital localized de-localized IT’S ABOUT THE MOLECULE NOT THE BOND…….

What is bond strength and bond length in H 2 ? How can we get that? Quantum mechanics, oribitals for the whole molecule and energies for all electrons – what distance? For the whole molecule – not just atomic orbital!

BONDING AND ANTIBONDING ORBITALS E

IDEAS ABOUT MO -Combine atomic orbitals, sometimes you get higher and sometimes you get lower energy -Remember electrons have wave functions -Constructive and destructive interference -Two possibilities http://winter.group.shef.ac.uk/orbitron/MOs/H2/1s1s-sigma/index.html

Wavefunctions, like waves, can INTERFERE Two main results: CONSTRUCTIVE and DESTRUCTIVE

and 1s 1s

COMPARE MO TO VB FOR H 2 Very similar because the bond is the molecule 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

What does the electron configuration for He 2 look like? HOW MANY ELECTRONS? WHERE DO THEY GO? BOND ORDER = ½(# BONDING - # ANTIBONDING)

POLL: CLICKER QUESTION + ? What is the bond order for H 2 CAN YOU DRAW THE LEWIS STRUCTURE?

What different ways can p-orbitals overlap?

NOTE: ANOTHER SET EXISTS AT RIGHT ANGLES TO THESE

POLL: CLICKER QUESTION Here are the MO’s for N 2 The highest energy electrons are in what molecular orbital? A. σ 2s B. σ * 2s C. σ 2p D. σ * 2p E. π * 2p IS IT DIAMAGNETIC OR PARAMAGNETIC?

Rules for Electron Configuration and Bond Order Calculation • 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* )

MOs can combine AO on dif atoms Diagram for CN - HOMO LUMO Bond Order? DIAMAGNETIC OR PARAMAGNETIC?

Methane What if its not a diatomic?

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

Important Information LM22 and HW posted Ungraded, just for extra practice: Laude LM Lecture 12 and 13