Hybridization
Covalent Bonding: Orbitals Chapter 09 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 The four bonds around C are of equal length and Energy Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Can you explain this based on your knowledge of electron energy levels? 6C 1s2 2s2 2p2 Bonding from s is Different from bonding From p. In addition the Angles should be within 900! Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 How to generate four equal orbitals? Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Hint: A key to wave mechanics is superposition Which is creating new waves from interference of old ones Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Let’s do some mixing Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Cross section of 3 an sp orbital. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 An energy-level diagram showing the 3 formation of four sp orbitals. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Hybridization 1s2 2s2 sp2 Ground state of C Promote electron at n=2 Hybridize at n=2 s px py pz s px py pz sp3 sp3 2s12p3 sp3 sp3 sp3 sp3 sp3 sp3 Four sp3 orbitals of equal length, energy and in tetrahedral shape Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 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. 13 Valence Bond Theory and NH3 N – 1s22s22p3 3 H – 1s1 2s 2px 2py 2pz If use the three 2p orbitals predict 900 Actual H-N-H bond angle is 107.30 How do you explain this? Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Consider the n=2 for N Original 2s Mix 1s and 3p And generate four 2px 2py 2pz sp3 sp3 sp3 sp3 Equivalent sp3 Hybridized orbitals 1 sp3 lone pair 3 bonding orbitals Which can accommodate The 1s1 electron from hydrogen Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 3 The nitrogen atom in ammonia is sp hybridized. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 2 An orbital energy-level diagram for sp hybridization. Note that one p orbital remains unchanged. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 19 When an s and two p orbitals are mixed to form a set 2 of three sp orbitals, one p orbital remains unchanged and is perpendicular to the plane of the hybrid orbitals. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 20 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 21 Figure 9.13: (a) The orbitals used to form the bonds in ethylene. (b) The Lewis structure for ethylene. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 22 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 23 Pi bond (p) – electron density above and below plane of nuclei Copyright©2000 bybetween Houghton 24 Sigma bond (s) – electron density the 2 atoms Mifflin Company. All rights reserved. of the bonding atoms Copyright©2000 by Houghton Mifflin Company. All rights reserved. 25 The s bonds in ethylene. Note that for each bond the shared electron pair occupies the region directly between the atoms. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 26 A sigma (s) bond centers along the internuclear axis. A pi (p) bond occupies the space above and below the internuclear axis. H p H C sC H H Copyright©2000 by Houghton Mifflin Company. All rights reserved. 27 (a)The orbitals used to form the bonds in ethylene. Copyright©2000 by Houghton Mifflin Company. All rights reserved. (b) The Lewis structure for ethylene. 28 The orbital energy-level diagram for the formation of sp hybrid orbitals on carbon. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 29 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 30 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. 31 The orbitals of an sp hybridized carbon atom. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 32 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 33 2 The orbital arrangement for an sp hybridized oxygen atom to form CO2. 8O 1s22s22p4 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 34 The hybrid orbitals in the CO2 molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 35 (a) The orbitals used to form the bonds in carbon dioxide. Note that the carbon-oxygen double bonds each consist of one s bond and one p bond. (b) The Lewis structure for carbon dioxide. 2sp orbitals from C to form two double bonds Copyright©2000 by Houghton Mifflin Company. All rights reserved. 36 (a) An sp hybridized nitrogen atom. (b) The s bond in the N2 molecule. (c) The two p bonds in N2 are formed when electron pairs are shared between two sets of parallel p orbitals. (d) The total bonding picture for N2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 37 Sigma (s) and Pi Bonds (p) 1 sigma bond Single bond Double bond 1 sigma bond and 1 pi bond Triple bond 1 sigma bond and 2 pi bonds How many s and p bonds are in the acetic acid (vinegar) molecule CH3COOH? H C H O H C O H s bonds = 6 + 1 = 7 p bonds = 1 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 38 10.5 How to generate more than 4 bonds? Remember the PCl5, SF6, etc… The s and 3p can generate 4 orbitals Include d orbitals to generate more! Copyright©2000 by Houghton Mifflin Company. All rights reserved. 39 s p p p d d d d d Hybridize 1s and 3p and 1d Result in 5 dsp3 orbitals 1 2 dsp3 dsp3 3 4 dsp3 dsp3 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 dsp3 40 A set of dsp3 hybrid orbitals on a phosphorus atom. Note that the set of five dsp3 orbitals has a trigonal bipyramidal arrangement. (Each dsp3 orbital also has a small lobe that is not shown in this diagram.) Copyright©2000 by Houghton Mifflin Company. All rights reserved. 41 (a) The PCl5 molecule. (b) The orbitals used to form the bonds in PCl5. The phosphorus uses a set of five dsp3 orbitals to share electron pairs with sp3 orbitals on the five chlorine atoms. The other sp3 orbitals on each chlorine atom hold lone pairs. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 42 How to form 6 orbitals? s p p p d d d d d Hybridize 1s and 3p and 2d 1 Result in 6 d2sp3 orbitals 2 3 4 5 d2sp3 ds2p3 d2sp3 6 d2sp3 d2sp3 d2sp3 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 43 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. 44 The Localized Electron Model Draw the Lewis structure(s) Determine the arrangement of electron pairs (VSEPR model). Specify the necessary hybrid orbital. All single bonds are hybridized and Sigma bond Double bond contains one Sigma and one Pi bonds while triple bond contains one sigma and two Pi bonds. Total number of electron pairs (bonded + unpaired electrons) decides the hybridization of the atom. Double and triple bonds are COUNTED as One Electron Pair. 2 electron pairs=SP, 3 electron pairs=SP2, 4 electron pairs=SP3,5 electron pairs=dSP3, 6 electron pairs=d2SP3 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 45 Molecular Orbitals (MO) Analagous to atomic orbitals for atoms, MOs are the quantum mechanical solutions to the organization of valence electrons in molecules. Remember bonds are waves and wave may be arranged in constructive or destructive interference. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 46 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 47 Types of MOs bonding: lower in energy than the atomic orbitals from which it is composed. antibonding(*): higher in energy (unstable) than the atomic orbitals from which it is composed. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 48 The combination of hydrogen 1s atomic orbitals to form molecular orbitals. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 49 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 50 Bonding and antibonding molecular orbitals (MOs). Copyright©2000 by Houghton Mifflin Company. All rights reserved. 51 (a) The molecular orbital energy-level diagram for the H2 molecule. (b) The shapes of the molecular orbitals are obtained by squaring the wave functions for MO1 and MO2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 52 A molecular orbital energylevel diagram for the H2 molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 53 The molecular orbital energy-level diagram for the H2 ion. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 54 The molecular orbital energy-level diagram for the He2 molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 55 The molecular orbital energy-level diagram for the Li2 molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 56 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 57 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. 58 The expected molecular orbital energy-level diagram for the B2 molecule. However, B2 is found to be Paramagnetic! Copyright©2000 by Houghton Mifflin Company. All rights reserved. 59 The correct molecular orbital energy-level diagram for the B2 molecule. When p-s mixing is allowed, the energies of the s2p and π2p orbitals are reversed. The two electrons from the B 2p orbitals now occupy separate, degenerate π2p molecular orbitals and thus have parallel spins. Therefore, this diagram explains the observed Copyright©2000 by Houghton paramagnetism of B2.Mifflin Company. All rights reserved. 60 (a) The three mutually perpendicular 2p orbitals on two adjacent boron atoms. Two pairs of parallel p orbitals can overlap as shown in (b) and (c), and the third pair can overlap head-on as shown in (d). Copyright©2000 by Houghton Mifflin Company. All rights reserved. 61 (a) The two p orbitals on the boron atom that overlap head-on produce two s molecular orbitals, one bonding and one antibonding. (b) Two p orbitals that lie parallel overlap to produce two p molecular orbitals, one bonding and one antibonding. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 62 The molecular orbital energy-level diagrams, bond orders, bond energies, and bond lengths for the diatomic molecules B2 through F2. Note that for O2 and F2 the s 2p orbital is lower in energy than the π2p orbitals. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 63 Paramagnetic Copyright©2000 by Houghton Mifflin Company. All rights reserved. Diamagnetic 64 Note that O2 is paramagnetic When liquid oxygen is poured into the space between the poles of a strong magnet, it remains there until it boils away. This attraction of liquid oxygen for the magnetic field demonstrates the paramagnetism of the O2 molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 65 Paramagnetism unpaired electrons attracted to induced magnetic field much stronger than diamagnetism Copyright©2000 by Houghton Mifflin Company. All rights reserved. 66 Bond Order (BO) Difference between the number of bonding electrons and number of antibonding electrons divided by two. # bonding electrons # antibonding electons BO = 2 Copyright©2000 by Houghton Mifflin Company. All rights reserved. 67 1 bond order = 2 bond order ½ ( Number of electrons in bonding MOs 1 - ½ Copyright©2000 by Houghton Mifflin Company. All rights reserved. Number of electrons in antibonding MOs ) 0 68 Molecular Orbital (MO) Configurations 1. The number of molecular orbitals (MOs) formed is always equal to the number of atomic orbitals combined. 2. The more stable the bonding MO, the less stable the corresponding antibonding MO. 3. The filling of MOs proceeds from low to high energies. 4. Each MO can accommodate up to two electrons. 5. Use Hund’s rule when adding electrons to MOs of the same energy. 6. The number of electrons in the MOs is equal to the sum of all the electrons on the bonding atoms. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 69 Outcomes of MO 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. N2 has a triple bond, and a correspondingly high bond energy. 4. O2 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. 70 Heteronuclear Molecules and similar? The molecular orbital energy-level diagram for the NO molecule. We assume that orbital order is the same as that for N2. The bond order is 2.5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 71 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. 72 Heteronuclear Molecules and similar? A partial molecular orbital energy-level diagram for the HF molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 73 The electron probability distribution in the bonding molecular orbital of the HF molecule. Note the greater electron density close to the fluorine atom. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 74 Combining LE and MO Models s bonds can be described as being localized. p bonding must be treated as being delocalized. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 75 Delocalized molecular orbitals are not confined between two adjacent bonding atoms, but actually extend over three or more atoms. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 76 (a) The benzene molecule consists of a ring of six carbon atoms with one hydrogen atom bound to each carbon. (b) Two of the resonance structures for the benzene molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 77 The s bonding system in the benzene molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 78 (a) The p molecular orbital system in benzene is formed by 2 combining the six p orbitals from the six sp hybridized carbon atoms. (b) The electrons in the resulting p molecular orbitals are delocalized over the entire ring of carbon atoms, giving six equivalent bonds. A composite of these orbitals is represented here. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 79 Electron density above and below the plane of the benzene molecule. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 80 - The resonance structures for O3 and NO3 . Note that it is the double bond that occupies various positions in the resonance structures. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 81 - (a) The p orbitals used to form the π bonding system in the NO3 ion. (b) A representation of the delocalization of the electrons in the π molecular orbital system of the NO3- ion. Copyright©2000 by Houghton Mifflin Company. 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