sp2, sp3, and Electronegativity (EN)

[yestomeds]

Hey all, simple chem question here for you guys.

Ok, so sp2 hybridized Carbons form shorter and stronger bonds with each other than do sp3 hybridized Carbons. Check.

Hm, but if we put it this way, then I don't understand:
can you explain how and why an sp2 Carbon is more electronegative.
And how and why it is more more polar and hence stronger.

? Thank you!

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[amy_k]

sp2 carbons have 33% s character and 66% p character.

sp3 carbons have 25%s and 75%p character. so sp2 have more s character than sp3. s orbitals hold electrons closer to the nucleus than p orbitals, so as s character increases so does electronegativity. The bonding electrons are pulled more strongly towards an sp2 carbon than sp3, so the bond is more polar. The fact that bonding electrons are under greater pull with an sp2 carbon also makes the bond shorter. Shorter bonds are stronger due to lower distance between the bonding atoms' nuclei.

Hope that helps.