Download - Lecture 11. Molecular Orbital Theory
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Take home quiz
Consider the following ACln species:
SCl2, OCl2, PCl3, SiCl4, SiCl62-
1) Determine the EGG and MGG of each compound
2) Arrange the compounds in decreasing Cl-A-Cl bond angles
3) Are all the molecules polar? Give the list of all the polar compounds from the given
4) Identify the orbitals involved in the bond A-Cl
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Answers
EGG: Tetrahedral MGG: Bent
SCl2
Angle Cl-S-Cl: < 109.5
Polar OCl2
EGG: Tetrahedral MGG: Bent
Angle Cl-O-Cl: < 109.5
Polar
sp3-p
sp3-p
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Answers
EGG: Tetrahedral MGG: Trigonal pyramidal
PCl3
Angle Cl-P-Cl: < 109.5
Polar
SiCl4 EGG: Tetrahedral MGG: Tetrahedral
Angle Cl-Si-Cl: 109.5
Nonpolar
sp3-p
sp3-p
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Answers
EGG: Octahedral MGG: Octahedral
SiCl62-
Angle Cl-Si-Cl: 180, 90
Nonpolar
2-
sp3d2 -p
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Answers
2) Arrange the compounds in decreasing Cl-A-Cl bond angles
Cl-Si-Cl > Cl-P-Cl > Cl-S-Cl = Cl-O-Cl
SiCl4 > PCl3 > SCl2 = OCl2
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Review
1. What are the two types of covalent bonding?
2. Explain how these two types of bond formed.
3. What is the shape of SeF4-molecule?
4. What are the orbital overlaps involved in the bonding of Se?
F
F F Se
F
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Review
5. How many bonds are present in the molecule _____?
6. What are the orbital overlaps involved in the bonding of _____?
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MOLECULAR ORBITALS
GENERAL CHEMISTRY
LECTURE
11
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1. Molecular Orbitals
2. Molecular Orbital Energy Level Diagrams
i. Homonuclear Diatomic Molecules
ii. Heteronuclear Diatomic Molecules
3. Bond Order and Bond Stability
Scope
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Molecular Orbital Theory
Electron orbitals delocalized over the entire molecule
Atomic orbitals on different atoms combined to form molecular orbitals (MOs).
Waves that describe atomic orbitals have both positive and negative amplitudes.
As MOs are formed the phases can interact constructively or destructively.
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Molecular Orbitals
There are two simple types of molecular orbitals that can be produced by the overlap of atomic orbitals.
1. (sigma) orbitals: head-on overlap of atomic orbitals
2. (pi) orbitals: side-on overlap of atomic orbitals
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Molecular Orbitals: s orbital
Two 1s atomic orbitals that overlap produce two molecular orbitals designated as:
1. 1s or bonding molecular orbital
2. *1s or antibonding molecular orbital.
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Energetically, the molecular orbitals split.
1. The 1s lies lower in energy.
2. The *1s is higher in energy.
Molecular Orbitals: s orbital
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The head-on overlap of two corresponding p atomic orbitals on different atoms, say 2px with 2px produces:
1. bonding orbital
2. antibonding orbital x2p*
x2p
Molecular Orbitals: p orbital
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Side overlap of two corresponding p atomic orbitals on different atoms (say 2py with 2py or 2pz with 2pz) produces:
1. or (both are bonding orbitals)
2. or (both are nonbonding orbitals) y2p
z2p
y2p*
z2p*
Molecular Orbitals: p orbital
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How are the orbitals filled with electrons?
Order of filling of MOs obeys same rules as for atomic orbitals:
Aufbau principle
Hunds Rule
Molecular Orbitals
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1s 1s
AO of H
AO of H MO of H2
1s
*1s
H2: 1s
Molecular Orbital Energy Level Diagram
2
Molecular hydrogen, H2 H: 1s1
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1s
AO of Li
AO of Li MO of Li2
1s
*1s
Li2: 2
1s *2
1s 2
2s
1s
2s
*2s
2s 2s
MO Diagram of Li2
Li: 1s22s1
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1s
AO of Be
AO of Be MO of Be2
1s
*1s
1s
2s
*2s
2s 2s
MO Diagram of Be2
Be2: 2
1s *2
1s 2
2s *2
2s
Be: 1s22s2
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MO Diagram of O2
1s
AO of O
AO Of O MO of O2
1s
*2p
1s
*1s
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2: 2
1s *2
1s 2
2s *2
2s 2
2p 22p
22p *
12p *
12p
O: 1s22s22p4
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MO Diagram of O2-
1s
AO of O
AO Of O MO of O2
1s
*2p
1s
*1s
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2-: 21s *
21s
22s *
22s
22p
22p 2
2p *2
2p *1
2p
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MO Diagram of O2+
1s
AO of O
AO Of O MO of O2
1s
*2p
1s
*1s
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2+: 21s *
21s
22s *
22s
22p
22p 2
2p *1
2p
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AO of O
AO Of O MO of O2
*2p
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
AO of O
AO Of O MO of O2
*2p
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2 O2-
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AO of O
AO Of O MO of O2
*2p
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
AO of O
AO Of O MO of O2
*2p
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2 O2+
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Exercise No.2
Draw the MO diagram of N2, N2- and N2
+.
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MO Diagram of N2-
1s
AO of O
AO Of O MO of O2
1s
*2p
1s
*1s
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
N2-: 21s *
21s
22s *
22s
22p
22p2
2p *1
2p
N: 1s22s22p3
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AO of O
AO Of O MO of O2
*2p
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2-
AO Of N
AO Of N MO of N2
*2p
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
N2-
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The stability of a bond is described by its bond order
The larger the bond order, the more stable the molecule or ion is.
The greater the bond order, the shorter the bond length and the greater the bond energy
2
orbitals gantibondinin e #orbitals bondingin e #=bo
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Bond Order and Bond Stability
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Magnetic Properties
Diamagnetic
Paramagnetic
all electrons are paired
presence of unpaired electron (s)
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1s 1s
AO of H
AO of H MO of H2
1s
*1s H2: 2
1s
Bond Order of H2
Bo = (2-0) = 1
Diamagnetic
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1s
AO of Li
AO of Li MO of Li2
1s
*1s
Li2: 2
1s *2
1s 2
2s
1s
2s
*2s
2s 2s
Bond Order of Li2
Bo = (4-2) = 1
Diamagnetic
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1s
AO of Be
AO Of Be MO of Be2
1s
*1s
Be2: 2
1s *2
1s 2
2s *2
2s
1s
2s
*2s
2s 2s
Bond Order of Be2
Bo = (4-4) = 0
-Be is stable as an atom
Diamagnetic
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Bond Order of O2
1s
AO of O
AO Of O MO of O2
1s
*2p
1s
*1s
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2: 2
1s *2
1s 2
2s *2
2s 2
2p 22p
22p *
12p *
12p
Bo = (10-6) = 2 Paramagnetic
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Bond Order of O2-
1s
AO of O
AO Of O MO of O2
1s
*2p
1s
*1s
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2-: 21s *
21s
22s *
22s
22p
22p 2
2p *2
2p *1
2p
Bo = (10-7) = 1.5 Paramagnetic
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Bond Order of O2+
1s
AO of O
AO Of O MO of O2
1s
*2p
1s
*1s
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
O2+: 21s *
21s
22s *
22s
22p
22p 2
2p *1
2p
Bo = (10-5) = 2.5 Paramagnetic
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Bond Order and Bond Stability
Stability:
O2 Bo =2
O2- Bo =1.5
O2+ Bo =2.5
O2+ > O2 > O2
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Bond Length: O2- > O2 > O2+
Bond Energy: O2+ > O2 > O2-
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Bond Order of N2-
1s
AO Of N
AO Of N MO of N2
1s
*2p
1s
*1s
2s
2s
2s
*2s
2p 2p
2p
*2p
*2p
2p 2p
N2-: 21s *
21s
22s *
22s
22p
22p2
2p *1
2p
Bo = (10-5) = 2.5 Paramagnetic
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Atomic orbitals of more electronegative element are lower in energy than the corresponding orbitals of less electronegative element
The closer the energy of MO is to the energy of one of the AO the more of the character of that AO it shows
Heteronuclear Diatomic Molecule
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1.Draw the MO diagram of F2 3 pts 2.Write the molecular orbital notation (electron configuration) of F2
-, F2 and F2+. 6 pts
3.Calculate the bond order of each species. 3 pts 4. Which is the most stable compound? 1 pt
Quiz 12 (13/13) May 8, 2013