1. Covalent Bonding: Orbitals What role do orbitals play in bonding?
Chapter 9
Covalent Bonding: Orbitals
What role do orbitals play in bonding?

2. Hybridization
Assumption: bonding happens between valence electrons of atoms - wrong.
Hybridization (mixing) of orbitals occurrs during bonding
When one s and three p orbitals are hybridized, an “sp3” orbital is formed (sp3 hybridization). This happens with equivalent tetrahedral atomic orbitals.
sp3 Hybridization Video

3. sp2 Hybridization
sp3 hybridized molecules have angles of 109.5°, so in molecules where trigonal planar arrangement (one plane, 120°) is required, sp3 hybridization can not be used.
These are formed with one 2s and two 2p orbitals, so it’s called sp2 hybridization. This leaves behind one 2p orbital (perpendicular to the plane).
sp2 Hybridization Video

4. Bond Types Sigma () vs. Pi ()
When bonds (sharing electrons) form where the pair is shared in an area centered on a line running between atoms, it is a sigma bond (lobes point towards each other)
This happens in single bonds…and in double/triple bonds (hold on)

5. Pi Bonds
When electron pairs occupy the space above and below a line joining the atoms
When orbitals are parallel
Double bonds consist of one sigma and one pi bond
Triple bonds consist of one sigma and two pi bonds
*Think “hot dog”

6. sp Hybridization
When there is a linear (180°) structure, sp3 and sp2 hybridization will not work
Involves one s and one p orbital being hybridized

7. Localized Electron Model
STEPS:
Draw the Lewis structure
Determine the arrangement of electron pairs using VSEPR
Specify the hybrid orbitals needed
Example: Predict the hybridization of each atom and describe the molecular structure of BF4-
Answer: boron is sp3, fluorine is sp3, molecular structure is tetrahedral

8. Examples… CO
Answer: each atom is sp hybridized, bonds present are a sigma and two pis, lone pairs are sp orbitals

9. # bonding - # antibonding
Bond Order
Def: the difference between the number of bonding electrons and the number of antibonding electrons divided by 2…
# bonding - # antibonding 2
Indicates bond strength: larger bond order = greater bond strength