Chapter 2 : Alkanes  Ch 2 contents

sp3 hybridization

Now let's see how hydridisation can account for each of these features, working towards methane then other alkanes:
 

the concept of hybridization
  • Promote an electron from 2s to 2p to create an excited state...
    • with 4 unpaired electrons we can form 4 bonds
    • these bonds would be from 1 x C2s-H1s interaction and 3 x C2p-H1s interactions
    • but these bonds will have different lengths and strengths
    • the 3 C-H bonds from the p orbitals maybe expected to have H-C-H bond angles of 90 degrees
  • "Blend" (i.e. hybridise) the s and the three p orbitals...
    • since we "mixed" 4 orbitals, we get a set of 4 sp3 orbitals
    • each sp3 hybrid contains a single unpaired electron
a sp3 hydrid orbital
creating the hybrids from an s and 3 p orbitals
The sp3 hybrid orbital looks like a "distorted" p orbital with unequal lobes.

The 4 sp3 hybrids point towards the corners of a tetrahedron.
 


 
 
  • For methane:
    • 4 equivalent C-H s bonds can be made by the interactions of Csp3 with a H1s
orbitals to bonds for methane
  • Now ethane, H3C-CH3 as a model for alkanes in general:
    • Both C are sp hybridised.
    • 6 C-H s bonds are made by the interaction of C sp3 with H1s orbitals (see the red arrows)
    • 1 C-C s bond is made by the interaction of C sp3 with another C sp3 orbital (see the green arrow)
orbitals to bonds for ethane

Summary



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