CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

Molecular Orbital TheoryDR. MIOY T. HUYNHYALE UNIVERSITYCHEMISTRY 161

FALL 2019

www.mioy.org/chem161

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

Reviewing Models of Chemical Structures

PROS CONSLewis Structure: simple; 2-dimensional only;

good for n = 1, 2 all electrons paired;cannot predict magnetism;falters for: odd number electrons,resonance, multiple structuresmany exceptions (n ≥ 3)

VSEPR: expansion of Lewis; all electrons paired;3-dimensional; cannot predict magnetism;gives info on angles

VALENCE BOND gives geometric info; electrons localized to atoms;THEORY: relatively simple cannot predict magnetism easily

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

Reviewing Models of Chemical Structures

PROS CONSLewis Structure: simple; 2-dimensional only;

good for n = 1, 2 all electrons paired;cannot predict magnetism;falters for: odd number electrons,resonance, multiple structuresmany exceptions (n ≥ 3)

VSEPR: expansion of Lewis; all electrons paired;3-dimensional; cannot predict magnetism;gives info on angles

VALENCE BOND gives geometric info; electrons localized to atoms;THEORY: relatively simple cannot predict magnetism easily

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

MOTIVATING MOLECULAR ORBITAL (MO) THEORY

A commonality among the Lewis model, VSEPR theory, and valence bond theory is that electrons in these models are mostly paired ➞ diamagnetic.

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

MOTIVATING MOLECULAR ORBITAL (MO) THEORY

A commonality among the Lewis model, VSEPR theory, and valence bond theory is that electrons in these models are mostly paired ➞ diamagnetic.

As such, they all have some difficulty describing chemical structures with:

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

MOTIVATING MOLECULAR ORBITAL (MO) THEORY

A commonality among the Lewis model, VSEPR theory, and valence bond theory is that electrons in these models are mostly paired ➞ diamagnetic.

As such, they all have some difficulty describing chemical structures with:• Odd numbers of electrons (called “radicals”)

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

MOTIVATING MOLECULAR ORBITAL (MO) THEORY

A commonality among the Lewis model, VSEPR theory, and valence bond theory is that electrons in these models are mostly paired ➞ diamagnetic.

As such, they all have some difficulty describing chemical structures with:• Odd numbers of electrons (called “radicals”)• Unpaired electrons ➞ paramagnetic

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

MOTIVATING MOLECULAR ORBITAL (MO) THEORY

A commonality among the Lewis model, VSEPR theory, and valence bond theory is that electrons in these models are mostly paired ➞ diamagnetic.

As such, they all have some difficulty describing chemical structures with:• Odd numbers of electrons (called “radicals”)• Unpaired electrons ➞ paramagnetic

DIAMAGNETIC all electrons paired (↿⇂) PARAMAGNETIC unpaired electrons (↿ or ⇂)

microscopicphenomenon

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

MOTIVATING MOLECULAR ORBITAL (MO) THEORY

A commonality among the Lewis model, VSEPR theory, and valence bond theory is that electrons in these models are mostly paired ➞ diamagnetic.

As such, they all have some difficulty describing chemical structures with:• Odd numbers of electrons (called “radicals”)• Unpaired electrons ➞ paramagnetic

DIAMAGNETIC all electrons paired (↿⇂) ➞ not attracted to poles of magnetPARAMAGNETIC unpaired electrons (↿ or ⇂) ➞ attracted to poles of magnet

microscopicphenomenon

macroscopicphenomenon

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

MOTIVATING MOLECULAR ORBITAL (MO) THEORY

A commonality among the Lewis model, VSEPR theory, and valence bond theory is that electrons in these models are mostly paired ➞ diamagnetic.

As such, they all have some difficulty describing chemical structures with:• Odd numbers of electrons (called “radicals”)• Unpaired electrons ➞ paramagnetic

DIAMAGNETIC all electrons paired (↿⇂) ➞ not attracted to poles of magnetPARAMAGNETIC unpaired electrons (↿ or ⇂) ➞ attracted to poles of magnet

microscopicphenomenon

macroscopicphenomenon

We need a model of chemical bonding that can capture this phenomenon!

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

VALENCE BOND vs. MOLECULAR ORBITAL

Valence Bond (VB) Theory

Mixing atomic orbitals (AOs) within an atom.

Molecular Orbital (MO) Theory

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

VALENCE BOND vs. MOLECULAR ORBITAL

Valence Bond (VB) Theory

Mixing atomic orbitals (AOs) within an atom.

Molecular Orbital (MO) TheoryEN

ERG

Y

↿⇂

1s

↿⇂

2s

↿⇂ ↿ ↿

2p

C

↿⇂ ↿⇂ ↿⇂ ↿⇂

sp3

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

VALENCE BOND vs. MOLECULAR ORBITAL

Valence Bond (VB) Theory

Mixing atomic orbitals (AOs) within an atom.

Molecular Orbital (MO) Theory

Mixing atomic orbitals (AOs) betweentwo (or more) atoms.

ENER

GY

↿⇂

1s

↿⇂

2s

↿⇂ ↿ ↿

2p

C

↿⇂ ↿⇂ ↿⇂ ↿⇂

sp3

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

VALENCE BOND vs. MOLECULAR ORBITAL

Valence Bond (VB) Theory

Mixing atomic orbitals (AOs) within an atom.

Molecular Orbital (MO) Theory

Mixing atomic orbitals (AOs) betweentwo (or more) atoms.

ENER

GY

↿⇂

1s

↿⇂

2s

↿⇂ ↿ ↿

2p

C

↿⇂ ↿⇂ ↿⇂ ↿⇂

sp3

ENER

GY

↿⇂

1s

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂

1s

↿⇂

2s

↿ ↿ ↿

2p

N

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

VALENCE BOND vs. MOLECULAR ORBITAL

Valence Bond (VB) Theory

Mixing atomic orbitals (AOs) within an atom.

Molecular Orbital (MO) Theory

Mixing atomic orbitals (AOs) betweentwo (or more) atoms.

ENER

GY

↿⇂

1s

↿⇂

2s

↿⇂ ↿ ↿

2p

C

↿⇂ ↿⇂ ↿⇂ ↿⇂

sp3

ENER

GY

↿⇂

1s

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂

1s

↿⇂

2s

↿ ↿ ↿

2p

N

How do these mix?

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

VALENCE BOND vs. MOLECULAR ORBITAL

Valence Bond (VB) Theory

Mixing atomic orbitals (AOs) within an atom.

(only valence electrons comprise bond)

Molecular Orbital (MO) Theory

Mixing atomic orbitals (AOs) betweentwo (or more) atoms.

(only valence electrons comprise bond)

ENER

GY

↿⇂

1s

↿⇂

2s

↿⇂ ↿ ↿

2p

C

↿⇂ ↿⇂ ↿⇂ ↿⇂

sp3

ENER

GY

↿⇂

1s

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂

1s

↿⇂

2s

↿ ↿ ↿

2p

N

How do these mix?

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory Molecular Orbital (MO) Theory

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

N2(MO)

How do these mix?

How do these mix?

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

N2(MO)

How do these mix?

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿⇂ ↿⇂

π2p*

N2(MO)

Don’t worry about ordering of MOs here.

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿⇂ ↿⇂

π2p*

N2(MO)

fill from bottom up

Don’t worry about ordering of MOs here.

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿⇂ ↿⇂

π2p*

N2(MO)

fill from bottom up

Don’t worry about ordering of MOs here.

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿⇂ ↿⇂

π2p*

N2(MO)

bonding orbitals

Don’t worry about ordering of MOs here.

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿⇂ ↿⇂

π2p*

N2(MO)

bonding orbitals

antibonding orbitals

Don’t worry about ordering of MOs here.

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) TheoryBO = ½ [bonding e– – antibonding e–]

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿⇂ ↿⇂

π2p*

N2(MO)

bonding orbitals

antibonding orbitals

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) TheoryBO = ½ [8 e– – 2 e–] = 3 (triple bond)

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿⇂ ↿⇂

π2p*

N2(MO)

bonding orbitals

antibonding orbitals

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF N2 (N = 1s22s22p3)

Valence Bond (VB) Theory

Each N atom is sp-hybridized (SN = 2).The second N’s electrons are in purple.

Molecular Orbital (MO) TheoryBO = ½ [8 e– – 2 e–] = 3 (triple bond)

ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N

↿⇂ ↿⇂

sp

↿⇂ ↿⇂

p

1 lone pair1 σ bond

2 π bonds ENER

GY

↿⇂

2s

↿ ↿ ↿

2p

N(AO)

↿⇂

2s

⇂ ⇂ ⇂

2p

N(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿⇂ ↿⇂

π2p*

N2(MO)

bonding orbitals

antibonding orbitals

DIAMAGNETIC

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF O2 (O = 1s22s22p4)

Valence Bond (VB) Theory Molecular Orbital (MO) Theory

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF O2 (O = 1s22s22p4)

Valence Bond (VB) Theory

Each O atom is sp2-hybridized (SN = 3).

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O

↿⇂ ↿⇂ ↿⇂

sp2

↿⇂

p

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF O2 (O = 1s22s22p4)

Valence Bond (VB) Theory

Each O atom is sp2-hybridized (SN = 3).The second O’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O

↿⇂ ↿⇂ ↿⇂

sp2

↿⇂

p

2 lone pairs1 σ bond

1 π bond

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF O2 (O = 1s22s22p4)

Valence Bond (VB) Theory

Each O atom is sp2-hybridized (SN = 3).The second O’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O

↿⇂ ↿⇂ ↿⇂

sp2

↿⇂

p

2 lone pairs1 σ bond

1 π bond ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O(AO)

↿⇂

2s

↿⇂ ⇂ ⇂

2p

O(AO)

σ2s

σ2s

*

↿⇂

σ2p

σ2p

*

π2p

π2p*

O2(MO)

bonding orbitals

antibonding orbitals

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF O2 (O = 1s22s22p4)

Valence Bond (VB) Theory

Each O atom is sp2-hybridized (SN = 3).The second O’s electrons are in purple.

Molecular Orbital (MO) Theory

ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O

↿⇂ ↿⇂ ↿⇂

sp2

↿⇂

p

2 lone pairs1 σ bond

1 π bond ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O(AO)

↿⇂

2s

↿⇂ ⇂ ⇂

2p

O(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿↿⇂ ↿

π2p*

O2(MO)

bonding orbitals

antibonding orbitals

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF O2 (O = 1s22s22p4)

Valence Bond (VB) Theory

Each O atom is sp2-hybridized (SN = 3).The second O’s electrons are in purple.

Molecular Orbital (MO) TheoryBO = ½ [8 e– – 4 e–] = 3 (double bond)

ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O

↿⇂ ↿⇂ ↿⇂

sp2

↿⇂

p

2 lone pairs1 σ bond

1 π bond ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O(AO)

↿⇂

2s

↿⇂ ⇂ ⇂

2p

O(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿↿⇂ ↿

π2p*

O2(MO)

bonding orbitals

antibonding orbitals

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF O2 (O = 1s22s22p4)

Valence Bond (VB) Theory

Each O atom is sp2-hybridized (SN = 3).The second O’s electrons are in purple.

Molecular Orbital (MO) TheoryBO = ½ [8 e– – 4 e–] = 3 (double bond)

ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O

↿⇂ ↿⇂ ↿⇂

sp2

↿⇂

p

2 lone pairs1 σ bond

1 π bond ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O(AO)

↿⇂

2s

↿⇂ ⇂ ⇂

2p

O(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿↿⇂ ↿

π2p*

O2(MO)

bonding orbitals

antibonding orbitals

UNPAIREDELECTRONS

CHEMISTRY 161 – FALL 2019 Dr. Mioy T. Huynh

THE CASE OF O2 (O = 1s22s22p4)

Valence Bond (VB) Theory

Each O atom is sp2-hybridized (SN = 3).The second O’s electrons are in purple.

Molecular Orbital (MO) TheoryBO = ½ [8 e– – 4 e–] = 2 (double bond)

ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O

↿⇂ ↿⇂ ↿⇂

sp2

↿⇂

p

2 lone pairs1 σ bond

1 π bond ENER

GY

↿⇂

2s

↿⇂ ↿ ↿

2p

O(AO)

↿⇂

2s

↿⇂ ⇂ ⇂

2p

O(AO)

↿⇂

σ2s

↿⇂

σ2s

*

↿⇂

σ2p

↿⇂

σ2p

*

↿⇂ ↿⇂

π2p

↿↿⇂ ↿

π2p*

O2(MO)

bonding orbitals

antibonding orbitals

PARAMAGNETIC

UNPAIREDELECTRONS