1. Oddities in Covalent Bonding

2. Hybridization
If you look the VALENCE orbital notation model of carbon, it seems that Carbon can only form 2 bonds.
We’re single . . .

3. But everywhere we see that C forms 4 bonds. For example……

4. So…. Something must be wrong with the way we explain bonding…..
What if the s & p orbitals were able to combine???????
This would make 4 NEW orbitals so each electron could have its own space
Now we’re all Single!

5. The result is 4 hybridized sp3 orbitals
making 4 unpaired valence electrons available for bonding.
I can bond
I can bond
I can bond
I can bond

6. Other hybrid orbitals
sp orbitals form when a 2s valence electron from Be is promoted to 2p
2px py pz 2s
sp hybrid
But we’re single, now…….
We’re already together & don’t bond
Be can now make 2 bonds

7. Examples
NOTICE: in every case Be has less than 8 valence electrons…… its an exception to the octet rule.

8. sp2 orbitals form in B when a 2s valence electron is promoted to the p orbital
2px py pz 2s
sp2 hybrid
B can now make 3 bonds

9. Examples
AGAIN NOTICE: B has only 6 e- surrounding it and it is stable!

10. Resonance Structures

11. Sometimes
it is possible to draw more than one correct / valid dot structure for a molecule

12. Ex #1. Sulfur dioxide
The electrons continuously switch between a double bond and a single bond.
Seriously? How do we know?

13. Bond length
Double bonds are shorter than single bonds. So when we measure the bonds in SO2 we should see this…..
But no!

14. In reality the bonds are the same length so……
In reality the bonds are the same length so……. A 1 ½ bond is formed from delocalized electrons in the molecule
Delocalized means that they can move (they don’t stay local)

15. Ex. #2 Carbonate CO3-2
It’s a 11/3 bond

16. Expanded Octets IF (and not usually) there are extra electrons after everything is stable, they go on the central atom.
Phosphorus pentachloride
Count your valence electrons and draw the Lewis dot structure.

17. Sulfur tetrafluoride
Count your valence electrons and draw the Lewis dot structure.

18. Network Solids Covalent Molecules that have properties of ionic solids
High m.p. temps
Hard solids at room temp
Crystal lattice structure
Its often difficult to tell where one molecule starts and another stops

19. Network solid examples

20. The End