See Handout on Website

1
See Handout on Website
2
See Handout on Website
3
To Determine Hybridization

• Steps (page 670)
• Draw Lewis Structures
• Determine Arrange of Electron Pairs
• Specify Hybrid Orbitals

Amount of hybridization matches number of
effective pairs i.e. s p2 3 pairs
4
Molecular Orbital Model

• A different model for describing bonding
• Hybridization an extension of Lewis Structures
  and VSEPR theory
• Molecular Orbitals an extension of atomic
  orbitals (chapter 12)

5
Atomic Orbitals A Refresher

• Shapes that describe the probability of finding
  an electron
• Orbitals have different energies
• Electrons fill lower energy orbitals first (in
  pairs)

6
Atomic Orbital Energies
7
Molecular Orbitals

• Different combinations of atomic orbitals
• Describe the probability of finding an electron
  in a molecular bond
• Each can hold two electrons

8
Molecular Orbitals of H2

• Two atomic orbitals form two molecular orbitals,
  by addition and subtraction

9

• Symmetric around line through nuclei (s)
• 1s orbitals no longer exist replaced by MOs
• MO1 is lower energy than AO, MO2 is higher

• MO1 is the Bonding MO (s1s)
• MO2 is the Antibonding MO (s1s)

10
Bond Order

• Bond Order The number of bonds between a pair of
  atoms
• From Lewis Structures O O bond order 2
• O S O ?? O S O bond order 1.5
• From MO Theory
• bonding electrons antibonding electrons
• 2

Bond Order
11

• Larger bond order greater bond strength
• Bond Order for H2?

12

• Bond Order for He2?

13
Li2

• Do we need both 1s and 2s orbitals?
• No. Make MOs from 2s AOs

14
Molecular Orbitals from p AOs
15
s MOs
p MOs
16
Expected Energy Diagram

• The Idea electrons prefer to be directly between
  nuclei, so s MO is lowest energy
• Note that this is not actually true for B2