E

Overlap of p wave orbitalsin the x direction

3 nodes

σ* (px)

σ (px)

Copyright 2002, K. Golestaneh

Overlap of p wave orbitalsin the y and z directions

E

π* (py)

π* (pz)

π (py)π (pz)Copyright 2002, K. Golestaneh

Degenerate orbitals

Degenerate orbitals

2s

1s

2p

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

Combining atomic p orbitals to molecular orbitals

2s2sσ (2s)

σ* (2s)

Combining atomic orbitals to form molecular orbitals

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

Ne2

E

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

F2

E

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

O2

E

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

σ Orbitalsbeing too close repeleach other!

Before!!!

N2

E

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

σ (2px) hashigher energythan π(2py ) !

After!!!

N2

E

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

C2

E

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

B2

E

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

Be2

E

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

2p 2p

2s2sσ (2s)

σ* (2s)

Li2

E

Copyright 2002, K. Golestaneh

E

Perfect energy match!Strongest bonding!

E

ok energy match!still good bonding!

E

poor energy match!weaker bonding!

E

Badly matched!very weak bonding!

E

no energy match!!(non-bonding electrons)

1. Atomic orbitals are “wave containers”2. An atom has infinite number of

orbitals (n=1 to n=∞)3. Electrons are the “wave contents”4. Core electrons are complete orbitals

that don’t contribute to bonding.5. Valence electrons (orbitals) cause

bonding. Filled valence sublevels don’t contribute to bonding.

6. The strength of a covalent bond is determined by the “energy matching” of orbitals involved.

7. Electrons that fill antibonding MOs, weaken the bond!

8. Orbital shape does matters for a strong overlap. (Px-Px overlap is stronger than Py-Py and Pz-Pz)

LUMO: Lowest Unoccupied MOHOMO: Highest Occupied MOSOMO: Singly-Occupied MO (free radicals)

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

O2

E

Copyright 2002, K. Golestaneh

LUMO

HOMO

HOMO-1

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

Copyright 2002, K. Golestaneh

σ (2px)

σ* (2px)

π*(2py) π*(2pz)

π(2py) π(2pz)

For species group 6-8 For species group 2-5

P-level filling order or molecular orbitals