Lecture 11. Molecular Orbital Theory

5/26/2018 Lecture 11. Molecular Orbital Theory

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Take home quiz

Consider the followingAClnspecies:

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 allthe 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

FF 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 ORBITALSGENERAL CHEMISTRY

LECTURE

11


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1. Molecular Orbitals2. 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 molecularorbitals (MOs).

Waves that describe atomic orbitals have both positive andnegative amplitudes.

As MOs are formed the phases can interact constructively ordestructively.


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Molecular Orbitals

There are two simple types of molecular orbitals thatcan 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 twomolecular orbitals designated as:

1. 1s or bonding molecular orbital2. *1s or antibonding molecular orbital.


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Energetically, the molecular orbitals split.1. The 1slies lower in energy.

2. The *1sis higher in energy.

Molecular Orbitals: s orbital


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The head-on overlap of two corresponding p atomicorbitals on different atoms, say 2pxwith 2pxproduces:

1. bonding orbital

2. antibonding orbitalx2p*

x2p

Molecular Orbitals: p orbital


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Side overlap of two corresponding p atomic orbitals on

different atoms (say 2pywith 2pyor 2pzwith 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

HundsRule

Molecular Orbitals


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1s 1s

AO

of H

AO

of HMO of H2

1s

*1s

H2: 1s

Molecular Orbital Energy Level Diagram

2

Molecular hydrogen, H2H: 1s1


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1s

AO

of Li

AO

of LiMO of Li2

1s

*1s

Li2: 2

1s*2

1s2

2s

1s

2s

*2s

2s2s

MO Diagram of Li2

Li: 1s

2

2s

1


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1s

AO

of Be

AO

of BeMO of Be2

1s

*1s

1s

2s

*2s

2s2s

MO Diagram of Be2

Be2: 2

1s*2

1s2

2s*2

2s

Be: 1s

2

2s

2


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MO Diagram of O2

1s

AO

of O

AO

Of OMO of O2

1s

*2p

1s

*1s

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

O2: 2

1s*2

1s2

2s*2

2s2

2p

2

2p2

2p*1

2p*1

2p

O: 1s22s22p4


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MO Diagram of O2-

1s

AO

of O

AO

Of OMO of O2

1s

*2p

1s

*1s

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

O2-: 21s*

21s

22s*

22s

22p

22p

22p

*22p

*12p


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MO Diagram of O2+

1s

AO

of O

AO

Of OMO of O2

1s

*2p

1s

*1s

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

O2+: 21s*

21s

22s*

22s

22p

2

2p2

2p*1

2p


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AO

of O

AO

Of OMO of O2

*2p

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

AO

of O

AO

Of OMO 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 OMO of O2

*2p

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

AO

of O

AO

Of OMO 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 OMO of O2

1s

*2p

1s

*1s

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

N2-: 21s*

21s

22s*

22s

22p

22p22p *12p

N: 1s22s22p3


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AO

of O

AO

Of OMO of O2

*2p

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

O2-

AO

Of N

AO

Of NMO 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

orbitalsgantibondinine#orbitalsbondingine#=bo

--

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 HMO of H2

1s

*1s H2: 2

1s

Bond Order of H2

Bo = (2-0) = 1Diamagnetic


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1s

AO

of Li

AO

of LiMO of Li2

1s

*1s

Li2: 2

1s*2

1s2

2s

1s

2s

*2s

2s2s

Bond Order of Li2

Bo = (4-2) = 1

Diamagnetic


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1s

AO

of Be

AO

Of BeMO of Be2

1s

*1s

Be2: 2

1s*2

1s2

2s*2

2s

1s

2s

*2s

2s2s

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 OMO of O2

1s

*2p

1s

*1s

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

O2: 21s*21s22s*22s22p22p

22p*

12p*

12p

Bo = (10-6) = 2

Paramagnetic


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Bond Order of O2-

1s

AO

of O

AO

Of OMO of O2

1s

*2p

1s

*1s

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

O2-

: 2

1s*2

1s2

2s*2

2s2

2p22p

22p*

22p*

12p

Bo = (10-7) = 1.5

Paramagnetic


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Bond Order of O2+

1s

AO

of O

AO

Of OMO of O2

1s

*2p

1s

*1s

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

O2+

: 2

1s*2

1s2

2s*2

2s2

2p22p

22p*

12p

Bo = (10-5) = 2.5

Paramagnetic


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Bond Order and Bond Stability

Stability:

O2Bo =2

O2-Bo =1.5

O2+Bo =2.5

O2+> O2> O2

-

Bond Length: O2- > O2> O2

+

Bond Energy:O

2

+> O2

> O2

-


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Bond Order of N2-

1s

AO

Of N

AO

Of NMO of N2

1s

*2p

1s

*1s

2s

2s

2s

*2s

2p 2p

2p

*2p

*2p

2p 2p

N2-: 21s*21s22s*22s22p22p

22p *

12p

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

-, F2and 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

Lecture 11. Molecular Orbital Theory

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