Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries...
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Transcript of Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries...
![Page 1: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/1.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Sections 9.5-9.8Molecular Geometriesand Bonding Theories
Chemistry, The Central Science, 11th editionBrown & LeMay
![Page 2: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/2.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
But it’s hard to imagine tetrahedral, trigonal bipyramidal, and other geometries arising from the atomic orbitals we recognize.
![Page 3: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/3.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
• Consider beryllium:– In its ground electronic
state, it would not be able to form bonds because it has no singly-occupied orbitals.
![Page 4: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/4.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
But if it absorbs the small amount of energy needed to promote an electron from the 2s to the 2p orbital, it can form two bonds.
![Page 5: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/5.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
• Mixing the s and p orbitals yields two degenerate orbitals that are hybrids of the two orbitals.– These sp hybrid orbitals have two lobes like a p orbital.– One of the lobes is larger and more rounded as is the s
orbital.
![Page 6: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/6.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
• These two degenerate orbitals would align themselves 180 from each other.
• This is consistent with the observed geometry of beryllium compounds: linear.
![Page 7: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/7.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
• With hybrid orbitals the orbital diagram for beryllium would look like this.
• The sp orbitals are higher in energy than the 1s orbital but lower than the 2p.
![Page 8: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/8.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
Using a similar model for boron leads to…
![Page 9: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/9.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
…three degenerate sp2 orbitals.
![Page 10: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/10.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
With carbon we get…
![Page 11: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/11.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
…four degenerate
sp3 orbitals.
![Page 12: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/12.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
For geometries involving expanded octets on the central atom, we must use d orbitals in our hybrids.
![Page 13: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/13.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
This leads to five degenerate sp3d orbitals…
…or six degenerate sp3d2 orbitals.
![Page 14: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/14.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Hybrid Orbitals
Once you know the electron-domain geometry, you know the hybridization state of the atom.
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MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Valence Bond Theory
• Hybridization is a major player in this approach to bonding.
• There are two ways orbitals can overlap to form bonds between atoms.
![Page 16: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/16.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Sigma () Bonds
• Sigma bonds are characterized by– Head-to-head overlap.– Cylindrical symmetry of electron density about the
internuclear axis.
![Page 17: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/17.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Pi () Bonds
• Pi bonds are characterized by– Side-to-side overlap.– Electron density
above and below the internuclear axis.
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MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Single Bonds
Single bonds are always bonds, because overlap is greater, resulting in a stronger bond and more energy lowering.
![Page 19: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/19.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Multiple Bonds
In a multiple bond one of the bonds is a bond and the rest are bonds.
![Page 20: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/20.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Multiple Bonds
• In a molecule like formaldehyde (shown at left) an sp2 orbital on carbon overlaps in fashion with the corresponding orbital on the oxygen.
• The unhybridized p orbitals overlap in fashion.
![Page 21: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/21.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Multiple Bonds
In triple bonds, as in acetylene, two sp orbitals form a bond between the carbons, and two pairs of p orbitals overlap in fashion to form the two bonds.
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MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Delocalized Electrons: Resonance
When writing Lewis structures for species like the nitrate ion, we draw resonance structures to more accurately reflect the structure of the molecule or ion.
![Page 23: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/23.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Delocalized Electrons: Resonance
• In reality, each of the four atoms in the nitrate ion has a p orbital.
• The p orbitals on all three oxygens overlap with the p orbital on the central nitrogen.
![Page 24: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/24.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Delocalized Electrons: Resonance
This means the electrons are not localized between the nitrogen and one of the oxygens, but rather are delocalized throughout the ion.
![Page 25: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/25.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Resonance
The organic molecule benzene has six bonds and a p orbital on each carbon atom.
![Page 26: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/26.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Resonance
• In reality the electrons in benzene are not localized, but delocalized.
• The even distribution of the electrons in benzene makes the molecule unusually stable.
![Page 27: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/27.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Molecular Orbital (MO) Theory
Though valence bond theory effectively conveys most observed properties of ions and molecules, there are some concepts better represented by molecular orbitals.
![Page 28: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/28.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Molecular Orbital (MO) Theory
• In MO theory, we invoke the wave nature of electrons.
• If waves interact constructively, the resulting orbital is lower in energy: a bonding molecular orbital.
![Page 29: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/29.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Molecular Orbital (MO) Theory
If waves interact destructively, the resulting orbital is higher in energy: an antibonding molecular orbital.
![Page 30: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/30.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
MO Theory
• In H2 the two electrons go into the bonding molecular orbital.
• The bond order is one half the difference between the number of bonding and antibonding electrons.
![Page 31: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/31.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
MO Theory
For hydrogen, with two electrons in the bonding MO and none in the antibonding MO, the bond order is(½)(bonding e- - antibonding e-)
12
(2 - 0) = 1
![Page 32: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/32.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
MO Theory
• In the case of He2, the bond order would be
12
(2 - 2) = 0
• Therefore, He2 does not exist.
![Page 33: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/33.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
MO Theory
• For atoms with both s and p orbitals, there are two types of interactions:– The s and the p orbitals
that face each other overlap in fashion.
– The other two sets of p orbitals overlap in fashion.
![Page 34: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/34.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
MO Theory
• The resulting MO diagram looks like this.
• There are both and bonding molecular orbitals and * and * antibonding molecular orbitals.
![Page 35: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/35.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
MO Theory
• The smaller p-block elements in the second period have a sizeable interaction between the s and p orbitals.
• This flips the order of the and molecular orbitals in these elements.
![Page 36: Molecular Geometries and Bonding © 2009, Prentice-Hall, Inc. Sections 9.5-9.8 Molecular Geometries and Bonding Theories Chemistry, The Central Science,](https://reader034.fdocuments.us/reader034/viewer/2022051000/56649e4d5503460f94b42c0b/html5/thumbnails/36.jpg)
MolecularGeometries
and Bonding
© 2009, Prentice-Hall, Inc.
Second-Row MO Diagrams