Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of...
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Transcript of Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of...
![Page 1: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/1.jpg)
Chapter 10: Covalent Bond Theories
Valence Bond Theory
Molecular Orbital TheoryFirst a couple of jokes… (You’ll need a laugh this chapter!)
If a bear from Yosemite and a bear from Alaska fall into the water, which one dissolves faster?
Which is lower energy, hamburger or steak?
My name is Bond - Ionic Bond; taken not shared!
![Page 2: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/2.jpg)
Valence Bond Theory – Covalent Bonds form from the __________ of atomic orbitals.
• Consider a BeF2 molecule:
F FBe
![Page 3: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/3.jpg)
Valence Bond TheoryF
1s22s22p5
F
1s22s22p5
Be
1s22s2
One unpaired e- One unpaired e-
No unpaired electrons
How can Be form covalent bonds with F if it doesn’t have unpaired electrons???
![Page 4: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/4.jpg)
Valence Bond Theory
Be
1s22s12p1
2 unpaired electrons
Promote one of the 2s e- to a 2p orbital
Be
1s22s2
no unpaired electrons
![Page 5: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/5.jpg)
Valence Bond Theory
F
1s22s22p5
F
1s22s22p5
Be
1s22s12p1
One unpaired e- One unpaired e-
2 unpaired electrons
Predicted overlaps:2s (Be) – 2p (F)2p (Be) – 2 p (F)
Implies two different kinds of Be – F bonds!
![Page 6: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/6.jpg)
Valence Bond Theory
• Both of the Be – F bonds in BeF2 are identical!
• The solution:– Mix the Be 2s orbital with one of the Be 2p
orbitals to form two hybrid orbitals• atomic orbitals formed by mixing 2 or more atomic
orbitals on an atom
![Page 7: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/7.jpg)
Valence Bond Theory
• When Be forms covalent bonds with two F, each sp hybrid orbital on the Be atom overlaps with a p orbital located on a F atom.
Be
1s 2sp 2p
F
1s22s22p5
F
1s22s22p5
![Page 8: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/8.jpg)
Valence Bond Theory
• The BeF2 molecule is linear.
• sp hybridization implies that the electron geometry around the central atom is linear.
![Page 9: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/9.jpg)
The sp2 hybrid orbitals in BF3.
![Page 10: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/10.jpg)
The sp3 hybrid orbitals in CH4.
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The sp3 hybrid orbitals in NH3.
![Page 12: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/12.jpg)
The sp3 hybrid orbitals in H2O.
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The sp3d hybrid orbitals in PCl5.
![Page 14: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/14.jpg)
The sp3d2 hybrid orbitals in SF6.
![Page 15: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/15.jpg)
Show the orbital hybridization of SF4
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![Page 17: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/17.jpg)
Multiple BondsMultiple Bonds All of the bonds shown thus far have been single bonds - which result in sigma bonds Sigma bondSigma bond () A bond where the line of electron A bond where the line of electron density is concentrated symmetrically along the line density is concentrated symmetrically along the line connecting the two atoms. Results from connecting the two atoms. Results from head to head head to head overlapoverlap of orbitals of orbitals
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Pi bondPi bond () A bond where the overlapping regions A bond where the overlapping regions exist above and below the internuclear axis.exist above and below the internuclear axis.
Pi bonds result from side to side overlap of atomic orbitals. Pi bonds cannot form from hybrid orbitals
A double bond consists of one sigma (hybrid) and one pure pi bond.
A triple bond consists of one hybrid sigma and 2 pure pi bonds
![Page 19: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/19.jpg)
Example: HExample: H22C=CHC=CH22
![Page 20: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/20.jpg)
Example: HExample: H22C=CHC=CH22
Only sigma bond pairs influence molecular geometry. What is the geometry around each central atom?
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Multiple Bonding:
• Formaldehyde: H2CO
• Acetylene: C2H2
Identify sigma and pi bonds in the following molecules and name the orbital hybridization involved.
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• Nitrogen gas
• Acetonitrile, CH3CN
![Page 23: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/23.jpg)
The paramagnetic properties of O2
Using the valence bond theory, explain the paramagnetism of oxygen gas.
![Page 24: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/24.jpg)
Molecular Orbital Theory –
• When 2 atomic orbitals overlap, two new molecular orbitals are formed:– Bonding molecular orbital
– Antibonding molecular orbital
Electrons are spread or delocalized over the whole molecule instead of remaining in atomic orbitals
Another theory for the formation of covalent bonds which explains phenomena for which the Valence Bond Theory can’t account .
![Page 25: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/25.jpg)
Molecular Orbital Theory• Bonding molecular orbital
– Addition of overlapping atomic orbitals results in an area of increased e- density; increased probability e- will be found here.
– lower energy than atomic orbital
Bonding MO
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Molecular Orbital Theory• Antibonding molecular orbital
– An area where the probability of finding an electron is reduced
• Results from subtracting one atomic orbital from the other
– higher energy than atomic orbital
Bonding MO
Antibonding MO
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![Page 28: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/28.jpg)
The one that is lower in energy is called the bonding orbital,
The one higher in energy is called an antibonding orbital.
These two new orbitals have different energies.
BONDING
ANTBONDING
Molecular Orbital (MO) TheoryMolecular Orbital (MO) Theory
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Molecular Orbital Theory
• The MO diagram for H2 molecule:
1s 1s
*1s
1sH atom H atom
H2 molecule
bonding electrons
Placing e-s in MO’s follows the Aufbau principle, Pauli’s and Hund’s Rule.
![Page 30: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/30.jpg)
Molecular Orbital Theory
• The MO diagram for He2 molecule:
1s 1s
*1s
1sHe atom He atom
He2 molecule
bonding electrons
antibonding electrons
Adding electrons to antibonding molecular orbitals destabilizes the molecule.
![Page 31: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/31.jpg)
Molecular Orbital Theory
• In MO Theory, the stability of a covalent bond can be related to its bond order:
• Bond order = (# bonding e- - # antibonding e-) 2– Old def.: # e- pairs / # links formed– Single bond: bond order = 1– Double bond: bond order = 2– Triple bond: bond order = 3
– Fractional bond orders also exist! (e.g. He2+1)
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Energy level diagrams / molecular Energy level diagrams / molecular orbital diagramsorbital diagrams
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Molecular Orbital Theory
• The bond order for H2 molecule:
Bond Order = (2 - 0) = 1
2
• The hydrogen atoms in an H2 molecule are held together by a single bond.
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Molecular Orbital Theory
• The bond order for an He2 molecule:
Bond order = (2 - 2) = 0
2
• No bond exists between two He atoms.
![Page 35: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/35.jpg)
Example: Example: LiLi22
Atomic orbitals combine to form molecular orbitals best when the atomic orbitals are of equal energy.
![Page 36: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/36.jpg)
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Electron Configurations for BElectron Configurations for B22 through Ne through Ne22
Second-Row Diatomic MoleculesSecond-Row Diatomic Molecules
![Page 38: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/38.jpg)
Relative MO energy levels for Period 2 homonuclear diatomic molecules.
MO energy levels for O2, F2, and Ne2
MO energy levels for B2, C2, and N2
without 2s-2p mixing
with 2s-2p mixing
![Page 39: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/39.jpg)
For B2, C2, and N2 the interaction is so strong that the 2p is pushed higher in energy than 2p orbitals
![Page 40: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/40.jpg)
Molecular Orbital Theory
Example: Complete the MO diagram for N2. Calculate the bond order.
# valence electrons for each N atom =
Total # of valence electrons =
![Page 41: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/41.jpg)
Molecular Orbital Theory
2s
2s
2p
2p
2p
2p
# bonding e- =
# antibonding e- =
Bond order =
![Page 42: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/42.jpg)
Molecular Orbital Theory
Example: Complete the MO diagram for the O2 molecule. Determine the bond order.
# valence electrons for each O atom =
Total # of valence electrons =
![Page 43: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/43.jpg)
Molecular Orbital Theory
2s
2s
2p
2p
2p
2p
# bonding e- =
# antibonding e- =
Bond order =
![Page 44: Chapter 10: Covalent Bond Theories Valence Bond Theory Molecular Orbital Theory First a couple of jokes… (You’ll need a laugh this chapter!) If a bear.](https://reader036.fdocuments.net/reader036/viewer/2022082217/56649e5c5503460f94b5417a/html5/thumbnails/44.jpg)
Isomers
1,1-dichloroethylene 1,2-dichloroethylene
cis-1,2-dichloroethylene trans-1,2-dichloroethylene