Covalent Bonding Orbitals orbitals just got stranger Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1

Localized Electron Model Lewis structures, VSEPR, and now, what type of atomic orbitals are used to share electrons. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2

3 Problem: all 4 bonds identical But C uses 2s, 2p orbitals. C 1s 2 2s 2 2p 2

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Hybridization The mixing of atomic orbitals to form special orbitals for bonding. The atoms are responding as needed to give the minimum energy for the molecule.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Figure 9.2 The Valence Orbitals on a Free Carbon Atom: 2s, 2p x, 2p y, and 2p z

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure 9.3 The Formation of sp 3 Hybrid Orbitals from the s and p orbitals

sp 3 hybridization (tetrahedron) We say that “carbon is sp 3 hybridized” or “carbon undergoes sp 3 hybridization” All 4 hybrid orbitals are identical Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7

8 Figure 9.4 Cross Section of an sp 3 Orbital

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Figure 9.5 An Energy-Level Diagram Showing the Formation of Four sp 3 Orbitals

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Figure 9.6 Tetrahedral Set of Four sp 3 Orbitals showing CH 4 arrangement

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 What about trig. pyramidal? The Nitrogen Atom in Ammonia is sp 3 Hybridized.

sp 2 hybridization (trig planar) ethylene Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Figure 9.8 The Hybridization of the s, p x, and p y Atomic Orbitals

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Figure 9.9 An Orbital Energy- Level Diagram for sp 2 Hybridization

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure 9.10 An sp 2 Hybridized C Atom notice that the extra P is perpen. To the 3 sp 2 orbitals

What does the extra “p” do? A sigma (  ) bond centers along the internuclear axis. (in ethylene these are the bonds using the sp 2 orbitals) A pi (  ) bond occupies the space above and below the internuclear axis. (in ethylene these are the bonds use the extra “p” orbitals) Note: a double bond is always a  and a  bond Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Figure 9.11 The  Bonds in Ethylene

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Figure 9.12 Sigma and Pi Bonding

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 Figure 9.13 The Orbitals for C 2 H 4

sp hybridization (linear) Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure 9.14 When One s Orbital and One p Orbital are Hybridized, a Set of Two sp Orbitals Oriented at 180 Degrees Results

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Figure 9.15 The Hybrid Orbitals in the CO 2 Molecule Note O is sp 2 hybridized, trig planar

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 The Orbital Energy-Level Diagram for the Formation of sp Hybrid Orbitals on Carbon (note: two 2p orbitals unchange)

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 24 Figure 9.17 The Orbitals of an sp Hybridized Carbon Atom

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 Figure 9.18 The Orbital Arrangement for an sp 2 Hybridized Oxygen Atom

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 Figure 9.19 The Orbitals for CO 2

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 Figure 9.20 The Orbitals for N 2 Note: sp hybridation for each N atom

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 28 dsp 3 hybridization trig. bipyramidal PCl 5

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 Set of dsp 3 Hybrid Orbitals on a Phosphorus Atom

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30 Figure 9.22 (a) The Structure of the PCl 5 Molecule (b) The Orbitals Used to Form the Bonds in PCl 5 (note each Cl is sp 3 hybridized)

Finally d 2 sp 3 hybridization SF 6 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 31

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 32 Figure 9.23 An Octahedral Set of d 2 sp 3 Orbitals on a Sulfur Atom

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33 The Localized Electron Model 4 Draw the Lewis structure(s) 4 Determine the arrangement of electron pairs (VSEPR model). 4 Specify the necessary hybrid orbitals.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34 Figure 9.24 The Relationship of the Number of Effective Pairs, Their Spatial Arrangement, and the Hybrid Orbital Set Required

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35 MO BETTA MODEL Since resonance is cumbersome and tedious, And odd – electron structures are not well accommodated by the simplified L.E. model, And no direct information about bond energies are given, And magnetic properties predicted by the L.E. model are not seen in the lab, We supplant the L.E. model with the M.O. model.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36 Molecular Orbitals (MO) Analagous to atomic orbitals for atoms, MOs are the quantum mechanical solutions to the organization of valence electrons in molecules.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37 Types of MOs bonding: lower in energy than the atomic orbitals from which it is composed. antibonding: higher in energy than the atomic orbitals from which it is composed.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38 Figure 9.25 The Combination of Hydrogen 1s Atomic Orbitals to Form Molecular Orbitals

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 39 Figure 9.27 Bonding and Antibonding Molecular Orbitals (MOs)

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 40 Figure 9.26 The Molecular Orbitals for H 2

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 41 Figure 9.28 The Molecular Orbital Energy- Level Diagram for the H 2 Molecule

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 42 Bond Order (BO) Difference between the number of bonding electrons and number of antibonding electrons divided by two.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 43 Figure 9.29 The Molecular Orbital Energy-Level Diagram for the H 2 - Ion

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 44 Figure 9.30 The Molecular Orbital Energy-Level Diagram for the He 2 Molecule

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 45 In order to participate in MOs, atomic orbitals must overlap in space. (Therefore, only valence orbitals of atoms contribute significantly to MOs.)

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 46 Figure 9.31 The Relative Sizes of the Lithium 1s and 2s Atomic Orbitals

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 47 Figure 9.32 The Molecular Orbital Energy-Level Diagram for the Li 2 Molecule

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 48 Figure 9.34 The Molecular Orbitals from p Atomic Orbitals

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 49 Figure 9.35 The Expected Molecular Orbital Energy-Level Diagram Resulting from the Combination of the 2p Orbitals on Two Boron Atoms

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 50 Figure 9.36 The Expected Molecular Orbital Energy-Level Diagram for the B 2 Molecule

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 51 Paramagnetism 4 unpaired electrons 4 attracted to induced magnetic field 4 much stronger than diamagnetism

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 52 Diamagnetism 4 paired electrons 4 repelled from induced magnetic field 4 much weaker than paramagnetism

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 53 Figure 9.37 Diagram of the Kind of Apparatus Used to Measure the Paramagnetism of a Sample

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 54 Figure 9.38 The Correct Molecular Orbital Energy- Level Diagram for the B 2 Molecule

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 55 Figure 9.39 Molecular Orbital Summary of Second Row Diatomics

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 56 Figure 9.41 The Molecule Orbital Energy- Level Diagram for the NO Molecule

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 57 Figure 9.42 The Molecular Orbital Energy- Level Diagram for Both the NO + and CN - Ions

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 58 Figure 9.43 A Partial Molecular Orbital Energy- Level Diagram for the HF Molecule

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 59 Figure 9.44 The Electron Probability Distribution in the Bonding Molecular Orbital of the HF Molecule

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 60 Outcomes of the MO Betta Model 1.As bond order increases, bond energy increases and bond length decreases. 2.Bond order is not absolutely associated with a particular bond energy. 3.N 2 has a triple bond, and a correspondingly high bond energy. 4.O 2 is paramagnetic. This is predicted by the MO model, not by the LE model, which predicts diamagnetism.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 61 Combining LE and MO Models  bonds can be described as being localized.  bonding must be treated as being delocalized.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 62 Figure 9.45 The Resonance Structures for O 3 and NO 3 -

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 63 Figure 9.46 A Benzene Ring

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 64 Figure 9.47 The Sigma System for Benzene

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 65 Figure 9.48 The Pi System for Benzene

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 66 Figure 9.49 The NO 3 - Ion