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Oddities in Covalent Bonding

Explore the peculiarities of covalent bonding and hybridization, from carbon forming 4 bonds to resonance structures like sulfur dioxide and carbonate. Learn about sp, sp2, and other hybrid orbitals, as well as network solids exhibiting ionic properties.

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Oddities in Covalent Bonding

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  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. sp hybrid Other hybrid orbitals • sp orbitals form when a 2svalence electron from Be is promoted to 2p 2px 2py 2pz 2s We’re already together & don’t bond But we’re single, now……. • 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 hybrid • sp2 orbitals form in B when a 2s valence electron is promoted to the p orbital 2px 2py 2pz 2s • 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 lengthso……. 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 OctetsIF (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

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