[duoheer]

If something is sp2 hybridized, does it have to include a double bond?
In resonance structures, can you form or remove pi/double bond? Even though the hybridization stays the same
thx

[Yggdrasil]

Most sp² hybridized atoms are involved in a pi bond of some sort.  However, carbocations and radicals are sp² hybridized (with the empty orbital and unpaired electron, respectively, occupying the p-orbital) and these species are not necessarily involved in pi bonds.

I'm not sure what you're asking in your second question.  Can you give an example?

[duoheer]

k an example would be
H3C-S-CH2 <------------> H3C-S=CH2
(a plus sign at C)              (a plus sign at S)

[Yggdrasil]

Yes, those would be two valid resonance structures.

[duoheer]

but then a pi bond is formed in the 2nd one

[Yggdrasil]

Remember that resonance structures are not completely accurate representations of the electronic structures of molecules.  The true structure of the molecule is a hybrid of the resonance structures.

In your example, both the methylene carbon and sulfur will be sp² hybridized, and the p-orbitals from these two atoms will overlap to form a pi bond.  However, the electrons in the pi-bond will not be equally shared between the two atoms.  As implied by the two resonance structures, the electrons will sometimes be very near to the sulfur while other times they will be equally shared between the sulfur and methylene carbon.

[duoheer]

i see, thx alot