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

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

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

Answers

EGG: Octahedral MGG: Octahedral

SiCl62-

Angle Cl-Si-Cl: 180, 90

Nonpolar

2-

sp3d2 -p

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

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

Review

5. How many bonds are present in the molecule _____?

6. What are the orbital overlaps involved in the bonding of _____?

MOLECULAR ORBITALS

GENERAL CHEMISTRY

LECTURE

11

1. Molecular Orbitals

2. Molecular Orbital Energy Level Diagrams

i. Homonuclear Diatomic Molecules

ii. Heteronuclear Diatomic Molecules

3. Bond Order and Bond Stability

Scope

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.

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

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.

Energetically, the molecular orbitals split.

1. The 1s lies lower in energy.

2. The *1s is higher in energy.

Molecular Orbitals: s orbital

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

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

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

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

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

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

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

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

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

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-

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+

Exercise No.2

Draw the MO diagram of N2, N2- and N2

+.

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

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-

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

--

Bond Order and Bond Stability

Magnetic Properties

Diamagnetic

Paramagnetic

all electrons are paired

presence of unpaired electron (s)

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

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

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

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

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

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

Bond Order and Bond Stability

Stability:

O2 Bo =2

O2- Bo =1.5

O2+ Bo =2.5

O2+ > O2 > O2

-

Bond Length: O2- > O2 > O2+

Bond Energy: O2+ > O2 > O2-

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

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

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